Found 65 papers in cond-mat
Date of feed: Wed, 27 Dec 2023 01:30:00 GMT

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Amine-Modified ZIF-8 for Enhanced CO$_2$ Capture: Synthesis, Characterization and Performance Evaluation. (arXiv:2312.14974v1 [cond-mat.mtrl-sci])
Viktorie Neubertova, Vaclav Svorcik, Zdenka Kolska

The urgent need for sustainable and innovative approaches to mitigate the increasing levels of atmospheric CO$_2$ necessitates the development of efficient methods for its removal. In this study, we focus on the synthesis and functionalization of metal-organic framework (MOF) ZIF-8 at room temperature to enhance its capacity for CO$_2$ capture. Specifically, we investigated the impact of four amino-compounds, namely tetraethylenepentamine (TEPA), hexadecylamine (HDA), ethanolamine (ELA), and cyclopropylamine (CPA), on the chemical structure, size, surface area and porosity and CO$_2$ capturing of ZIF-8 powder. By varying concentrations of the amino-compounds, we examined their influence on the ZIF-8 properties. These results highlight the potential of simple synthesis and functionalization techniques for MOFs in enhancing their CO$_2$ capture capabilities. The findings from this study offer new opportunities for the development of strategies to mitigate CO$_2$ emissions using MOFs.

Enhanced Ferromagnetism in Monolayer Cr2Te3 via Topological Insulator Coupling. (arXiv:2312.15028v1 [cond-mat.mtrl-sci])
Yunbo Ou, Murod Mirzhalilov, Norbert M. Nemes, Jose L. Martinez, Mirko Rocci, Austin Akey, Wenbo Ge, Dhavala Suri, Yiping Wang, Haile Ambaye, Jong Keum, Mohit Randeria, Nandini Trivedi, Kenneth S. Burch, David C. Bell, Weida Wu, Don Heiman, Valeria Lauter, Jagadeesh S. Moodera, Hang Chi

Exchange-coupled interfaces are pivotal in exploiting two-dimensional (2D) ferromagnetism. Due to the extraordinary correlations among charge, spin, orbital and lattice degrees of freedom, layered magnetic transition metal chalcogenides (TMCs) bode well for exotic topological phenomena. Here we report the realization of wafer-scale Cr2Te3 down to monolayer (ML) on insulating SrTiO3(111) substrates using molecular beam epitaxy. Robust ferromagnetism emerges in 2D Cr2Te3 ML with a Curie temperature TC = 17 K. Moreover, when Cr2Te3 is proximitized with topological insulator (TI) (Bi,Sb)2Te3, the magnetism becomes stronger -- for 1 ML, TC increases to 30 K, while for 2 ML it boosts from 65 K to 82 K. Our experiments and theory strongly indicate that the Bloembergen-Rowland interaction is likely a universal aspect of TC enhancement in TI-coupled magnetic heterostructures. The topological-surface-enhanced magnetism in 2D TMC enables further exchange coupling physics and quantum hybrid studies, including paving the way to realize interface-modulated topological electronics.

Unusual magnetism of the axion-insulator candidate Eu$_5$In$_2$Sb$_6$. (arXiv:2312.15054v1 [cond-mat.str-el])
M. C. Rahn, M. N. Wilson, T. J. Hicken, F. L. Pratt, C. Wang, F. Orlandi, D. D. Khalyavin, P. Manuel, L. S. I. Veiga, A. Bombardi, S. Francoual, P. Bereciartua, A. S. Sukhanov, J. D. Thompson, S. M. Thomas, P. F. S. Rosa, T. Lancaster, F. Ronning, M. Janoschek

Eu$_5$In$_2$Sb$_6$ is a member of a family of orthorhombic nonsymmorphic rare-earth intermetallics that combines large localized magnetic moments and itinerant exchange with a low carrier density and perpendicular glide planes. This may result in special topological crystalline (wallpaper fermion) or axion insulating phases. Recent studies of Eu$_5$In$_2$Sb$_6$ single crystals have revealed colossal negative magnetoresistance and multiple magnetic phase transitions. Here, we clarify this ordering process using neutron scattering, resonant elastic X-ray scattering, muon spin-rotation, and magnetometry. The nonsymmorphic and multisite character of Eu$_5$In$_2$Sb$_6$ results in coplanar noncollinear magnetic structure with an Ising-like net magnetization along the $a$ axis. A reordering transition, attributable to competing ferro- and antiferromagnetic couplings, manifests as the onset of a second commensurate Fourier component. In the absence of spatially resolved probes, the experimental evidence for this low-temperature state can be interpreted either as an unusual double-$q$ structure or in a phase separation scenario. The net magnetization produces variable anisotropic hysteretic effects which also couple to charge transport. The implied potential for functional domain physics and topological transport suggests that this structural family may be a promising platform to implement concepts of topological antiferromagnetic spintronics.

Engineering Plateau Phase Transition in Quantum Anomalous Hall Multilayers. (arXiv:2312.15072v1 [cond-mat.mes-hall])
Deyi Zhuo, Ling-Jie Zhou, Yi-Fan Zhao, Ruoxi Zhang, Zi-Jie Yan, Annie G. Wang, Moses H. W. Chan, Chao-Xing Liu, Chui-Zhen Chen, Cui-Zu Chang

The plateau phase transition in quantum anomalous Hall (QAH) insulators corresponds to a quantum state wherein a single magnetic domain gives way to multiple magnetic domains and then re-converges back to a single magnetic domain. The layer structure of the sample provides an external knob for adjusting the Chern number C of the QAH insulators. Here, we employ molecular beam epitaxy (MBE) to grow magnetic topological insulator (TI) multilayers with an asymmetric layer structure and realize the magnetic field-driven plateau phase transition between two QAH states with odd Chern number change {\Delta}C. In multilayer structures with C=+-1 and C=+-2 QAH states, we find two characteristic power-law behaviors between temperature and the scaling variables on the magnetic field at transition points. The critical exponents extracted for the plateau phase transitions with {\Delta}C=1 and {\Delta}C=3 in QAH insulators are found to be nearly identical, specifically, k1~0.390+-0.021 and k2~0.388+-0.015, respectively. We construct a four-layer Chalker-Coddington network model to understand the consistent critical exponents for the plateau phase transitions with {\Delta}C=1 and {\Delta}C=3. This work will motivate further investigations into the critical behaviors of plateau phase transitions with different {\Delta}C in QAH insulators and provide new opportunities for the development of QAH chiral edge current-based electronic and spintronic devices.

Two-dimensional topological paramagnets protected by $\mathbb{Z}_3$ symmetry: Properties of the boundary Hamiltonian. (arXiv:2312.15095v1 [cond-mat.str-el])
Hrant Topchyan, Vasilii Iugov, Mkhitar Mirumyan, Tigran S. Hakobyan, Tigran A. Sedrakyan, Ara G. Sedrakyan

We systematically construct two-dimensional $\mathbb{Z}_3$ symmetry-protected topological (SPT) three-state Potts paramagnets with gapless edge modes on a triangular lattice. First, we study microscopic lattice models for the gapless edge and, using the density-matrix renormalization group (DMRG) approach, investigate the finite size scaling of the low-lying excitation spectrum and the entanglement entropy. Based on the obtained results, we identify the universality class of the critical edge, namely the corresponding conformal field theory and the central charge. Finally, we discuss the inherent symmetries of the edge models and the emergent winding symmetry distinguishing between two SPT phases. As a result, the two topologically nontrivial and the trivial phases define a general one-dimensional chain supporting a tricriticality, which we argue supports a gapless SPT order in one dimension.

Stable Higher-Order Topological Dirac Semimetals with $\mathbb{Z}_2$ Monopole Charge in Alternating-twisted Multilayer Graphenes and beyond. (arXiv:2312.15131v1 [cond-mat.mes-hall])
Shifeng Qian, Yongpan Li, Cheng-Cheng Liu

We demonstrate that a class of stable $\mathbb{Z}_2$ monopole charge Dirac point ($\mathbb{Z}_2$DP) phases can robustly exist in real materials, which surmounts the understanding: that is, a $\mathbb{Z}_2$DP is unstable and generally considered to be only the critical point of a $\mathbb{Z}_2$ nodal line ($\mathbb{Z}_2$NL) characterized by a $\mathbb{Z}_2$ monopole charge (the second Stiefel-Whitney number $w_2$) with space-time inversion symmetry but no spin-orbital coupling. For the first time, we explicitly reveal the higher-order bulk-boundary correspondence in the stable $\mathbb{Z}_2$DP phase. We propose the alternating-twisted multilayer graphene, which can be regarded as 3D twisted bilayer graphene (TBG), as the first example to realize such stable $\mathbb{Z}_2$DP phase and show that the Dirac points in the 3D TBG are essential degenerate at high symmetric points protected by crystal symmetries and carry a nontrivial $\mathbb{Z}_2$ monopole charge ($w_2=1$), which results in higher-order hinge states along the entire Brillouin zone of the $k_z$ direction. By breaking some crystal symmetries or tailoring interlayer coupling we are able to access $\mathbb{Z}_2$NL phases or other $\mathbb{Z}_2$DP phases with hinge states of adjustable length. In addition, we present other 3D materials which host $\mathbb{Z}_2$DPs in the electronic band structures and phonon spectra. We construct a minimal eight-band tight-binding lattice model that captures these nontrivial topological characters and furthermore tabulate all possible space groups to allow the existence of the stable $\mathbb{Z}_2$DP phases, which will provide direct and strong guidance for the realization of the $\mathbb{Z}_2$ monopole semimetal phases in electronic materials, metamaterials and electrical circuits, etc.

Flat bands without twists: periodic holey graphene. (arXiv:2312.15165v1 [cond-mat.mes-hall])
Abdiel de Jesús Espinosa-Champo, Gerardo G. Naumis

\textit{Holey Graphene} (HG) is a widely used graphene material for the synthesis of high-purity and highly crystalline materials. In this work, we explore the electronic properties of a periodic distribution of lattice holes, demonstrating the emergence of flat bands with compact localized states. It is shown that the holes break the bipartite sublattice and inversion symmetries, inducing gaps and a nonzero Berry curvature. Moreover, the folding of the Dirac cones from the hexagonal Brillouin zone (BZ) to the holey superlattice rectangular BZ of HG with sizes proportional to an integer $n$ times the graphene's lattice parameter leads to a periodicity in the gap formation such that $n \equiv 0$ (mod $3$). Meanwhile, it is shown that if $n \equiv \pm 1$ (mod $3$), a gap emerges where Dirac points are folded along the $\Gamma-X$ path. The low-energy hamiltonian for the three central bands is also obtained, revealing that the system behaves as an effective $\alpha-\mathcal{T}_{3}$ graphene material. Therefore, a simple protocol is presented here that allows obtaining flat bands at will. Such bands are known to increase electron-electron correlated effects. This work provides an alternative system, much easier to build than twisted systems, to obtain highly correlated quantum phases.

Reduction of Magnetic Interaction Due to Clustering in Doped Transition-Metal Dichalcogenides: A Case Study of Mn, V, Fe-Doped $\rm WSe_2$. (arXiv:2312.15171v1 [cond-mat.mtrl-sci])
Sabyasachi Tiwari, Maarten Van de Put, Bart Soree, Christopher Hinkle, William G. Vandenberghe

Using Hubbard U corrected density functional theory calculations, lattice Monte-Carlo, and spin-Monte-Carlo simulations, we investigate the impact of dopant clustering on the magnetic properties of WSe2~doped with period four transition metals. We use manganese (Mn) and iron (Fe) as candidate n-type dopants and vanadium (V) as the candidate p-type dopants, substituting the tungsten (W) atom in WSe2. Specifically, we determine the strength of the exchange interaction in the Fe-, Mn-, and V-doped WSe2~ in the presence of clustering. We show that the clusters of dopants are energetically more stable than discretely doped systems. Further, we show that in the presence of dopant clustering, the magnetic exchange interaction significantly reduces because the magnetic order in clustered WSe2~becomes more itinerant. Finally, we show that the clustering of the dopant atoms has a detrimental effect on the magnetic interaction, and to obtain an optimal Curie temperature, it is important to control the distribution of the dopant atoms.

Exact ground state of interacting electrons in magic angle graphene. (arXiv:2312.15314v1 [math-ph])
Simon Becker, Lin Lin, Kevin D. Stubbs

One of the most remarkable theoretical findings in magic angle twisted bilayer graphene (TBG) is the emergence of ferromagnetic Slater determinants as exact ground states for the interacting Hamiltonian at the chiral limit. This discovery provides an explanation for the correlated insulating phase which has been experimentally observed at half filling. This work is the first mathematical study of interacting models in magic angle graphene systems. These include not only TBG but also TBG-like systems featuring four flat bands per valley, and twisted trilayer graphene (TTG) systems with equal twist angles. We identify symmetries of the Bistritzer-MacDonald Hamiltonian that are responsible for characterizing the Hartree-Fock ground states as zero energy many-body ground states. Furthermore, for a general class of Hamiltonian, we establish criteria that the ferromagnetic Slater determinants are the unique ground states within the class of uniformly half-filled, translation invariant Slater determinants. We then demonstrate that these criteria can be explicitly verified for TBG and TBG-like systems at the chiral limit, using properties of Jacobi-$\theta$ and Weierstrass-$\wp$ functions.

Energy conversion in thermoelectric materials of SnSSe and SnS$_2$: a Monte-Carlo simulation of Boltzmann transport equation. (arXiv:2312.15331v1 [cond-mat.mes-hall])
Seyedeh Ameneh Bahadori, Zahra Shomali

In the present work, thermal transport and energy conversation in two thermoelectrically efficient candidates of Janus SnSSe and SnS$_2$ are investigated within the non-equilibrium Monte Carlo simulation of phonon Boltzmann equation. The phonon analysis is performed to determine the contributed phonons in heat transport. The results present that the dominant participating phonons are longitudinal acoustic ones while the least belongs to the transverse acoustic (TA) mode. Both materials reached the very high maximum temperature in response to the implied wasted heat. This is attributed to the low presence of the critical TA phonons. Also, the temperature profile achieved during the heating and cooling of the materials is studied. It is obtained that the heat propagation through the SnS$_2$ is, at first, swifter, which results in a temperature gradient through the whole material which is less than that of the SnSSe. As the time passes, the heat transfer that is directly related to the material thermal conductivity, slows down. So, the behavior of the SnS$_2$ and SnSSe, in case of the heat propagation status, becomes similar. More, the behavior of the thermoelectric figure of merit (zT), the efficiency ($\eta$), and the generated voltage have been figured out. It is stated that the higher zT and $\eta$ do not guarantee a larger generated Seebeck voltage. This is true, while the generated Seebeck voltage is related to the temperature difference between the heated and the cold junction. Accordingly, how far the temperature of matter rises in response to the implied wasted heat is related to the obtained voltage. Mainly, it is presented that the maximum temperature that a material achieves, alongside the temperature gradient and material property Seebeck coefficient, are essential in introducing thermoelectrically efficient materials with reasonable thermal to electrical energy conversion.

Lifshitz Transition and Band Structure Renormalization in Alkali Metal Intercalated 1Tprime-MoTe2. (arXiv:2312.15360v1 [cond-mat.mtrl-sci])
Joohyung Park, Ayan N. Batyrkhanov, Jonas Brandhoff, Marco Gruenewald, Felix Otto, Maximilian Schaal, Saban Hus, Torsten Fritz, Florian Göltl, An-Ping Li, Oliver L.A. Monti

MoTe2 is a paradigmatic van der Waals layered semimetal with two energetically close electronic phases, the topologically trivial 1Tprime and the low-temperature Td type-II Weyl semimetal phase. The ability to manipulate this phase transition, perhaps towards occurring near room temperature, would open new avenues for harnessing the full potential of Weyl semimetals for high-efficiency electronic and spintronic applications. Here, we show that potassium dosing on 1Tprime-MoTe2 induces a Lifshitz transition by a combination of angle-resolved photoemission spectroscopy, scanning tunneling microscopy, x-ray spectroscopy and density functional theory. While the electronic structure shifts rigidly for small concentrations of K, MoTe2 undergoes significant band structure renormalization for larger concentrations. Our results demonstrate that the origin of this electronic structure change stems from alkali metal intercalation. We show that these profound changes are caused by effectively decoupling the 2D sheets, bringing K-intercalated 1Tprime-MoTe2 to the quasi-2D limit, but do not cause a topological phase transition.

Observation of a new three-dimensional Dirac-like dispersion in the type-II Dirac semimetals PtTe2 and PdTe2. (arXiv:2312.15371v1 [cond-mat.mes-hall])
Ivan Pelayo, Derek Bergner, Archibald J. Williams, Jiayuwen Qi, Mahfuzun Nabi, Warren L. B. Huey, Luca Moreschini, Ziling Deng, Jonathan Denlinger, Alessandra Lanzara, Wolfgang Windl, Joshua Goldberger, Claudia Ojeda-Aristizabal

PtTe$_2$ and PdTe$_2$ are among the first transition metal dichalcogenides that were predicted to host type-II Dirac fermions, exotic particles prohibited in free space. These materials are layered and air-stable, which makes them top candidates for technological applications that take advantage of their anisotropic magnetotransport properties. Here, we provide a detailed characterization of the electronic structure of PtTe$_2$ and PdTe$_2$ using Angle Resolved Photoemission Spectroscopy ARPES and Density Functional Theory DFT calculations, unveiling a new three-dimensional Dirac-like dispersion in these materials. Through the use of circularly polarized light, we report a different behavior of such dispersion in PdTe$_2$ compared to PtTe$_2$, that we relate to our DFT calculations. Additionally, our circular dichroism data shows a sharp difference between the known type-II Dirac cones and the topologically protected surface states in these materials. Finally, we present an analysis that links our experimental and theoretical data to the different symmetries associated to the crystallographic space group shared by PtTe$_2$ and PdTe$_2$. Our work provides a useful reference for the ARPES characterization of other transition metal dichalcogenides with topological properties and illustrates the use of circular dichroism as an additional tool to differentiate the topological character of two otherwise equivalent band dispersions and to identify new dispersions.

Quantum-criticality in twisted bi-layer graphene. (arXiv:2312.15410v1 [cond-mat.str-el])
C. M. Varma

We show that the particular loop-current order for twisted bi-layer graphene (TBG) at the carbon length-scale together with modulations on the moir\'e length scale proposed by Blutinck et al. maps to the xy model. Some experimental evidence in unstrained TBG at various fillings is consistent with this order at both scales while strained samples appear to show such an order at the carbon length scale but a kekule order at the moir\'e length scale. We pay special attention to deriving the coupling of fermions to the fluctuations of the xy model. The previous solution of the quantum xy model coupled to the fermions serves three purposes. (1) derivation of the $\omega/T$ scaling of the propagator of the fluctuations whose coupling to fermions gives the observed linear in temperature resistivity and other marginal Fermi-liquid properties which could tested in future experiments. (2) It provides the topological defects to which an externally applied magnetic field couples to give a resistivity proportional to $H_z$, and (3) it provides the mechanism for instability of the quantum fluctuating state to superconductivity in d-wave symmetry. Further experiments are required to ascertain the assumed symmetries of the order.

DPA-2: Towards a universal large atomic model for molecular and material simulation. (arXiv:2312.15492v1 [physics.chem-ph])
Duo Zhang, Xinzijian Liu, Xiangyu Zhang, Chengqian Zhang, Chun Cai, Hangrui Bi, Yiming Du, Xuejian Qin, Jiameng Huang, Bowen Li, Yifan Shan, Jinzhe Zeng, Yuzhi Zhang, Siyuan Liu, Yifan Li, Junhan Chang, Xinyan Wang, Shuo Zhou, Jianchuan Liu, Xiaoshan Luo, Zhenyu Wang, Wanrun Jiang, Jing Wu, Yudi Yang, Jiyuan Yang, Manyi Yang, Fu-Qiang Gong, Linshuang Zhang, Mengchao Shi, Fu-Zhi Dai, Darrin M. York, Shi Liu, Tong Zhu, Zhicheng Zhong, Jian Lv, Jun Cheng, Weile Jia, Mohan Chen, Guolin Ke, Weinan E, Linfeng Zhang, Han Wang

The rapid development of artificial intelligence (AI) is driving significant changes in the field of atomic modeling, simulation, and design. AI-based potential energy models have been successfully used to perform large-scale and long-time simulations with the accuracy of ab initio electronic structure methods. However, the model generation process still hinders applications at scale. We envision that the next stage would be a model-centric ecosystem, in which a large atomic model (LAM), pre-trained with as many atomic datasets as possible and can be efficiently fine-tuned and distilled to downstream tasks, would serve the new infrastructure of the field of molecular modeling. We propose DPA-2, a novel architecture for a LAM, and develop a comprehensive pipeline for model fine-tuning, distillation, and application, associated with automatic workflows. We show that DPA-2 can accurately represent a diverse range of chemical systems and materials, enabling high-quality simulations and predictions with significantly reduced efforts compared to traditional methods. Our approach paves the way for a universal large atomic model that can be widely applied in molecular and material simulation research, opening new opportunities for scientific discoveries and industrial applications.

Coalescence of immiscible droplets in liquid environments. (arXiv:2312.15500v1 [physics.flu-dyn])
Huadan Xu, Tianyou Wang, Zhizhao Che

Hypothesis: Droplet coalescence process is important in many applications and has been studied extensively when two droplets are surrounded by gas. However, the coalescence dynamics would be different when the two droplets are surrounded by an external viscous liquid. The coalescence of immiscible droplets in liquids has not been explored. Experiments: In the present research, the coalescence of two immiscible droplets in low- and high-viscosity liquids is investigated and compared with their miscible counterparts experimentally. The coalescence dynamics is investigated via high-speed imaging, and theoretical models are proposed to analyze the growth of the liquid bridge. Findings: We find that, the liquid bridge $r$ evolves differently due to the constraint from the triple line in the bridge region, which follows $r\propto {{t}^{{2}/{3}}}$ for low-viscosity surroundings. While for high-viscosity surroundings, the liquid bridge grows at a constant velocity ${{u}_{r}}$ which varies with the surrounding viscosity ${{\mu }_{s}}$ as ${{u}_{r}}\propto {{\mu }_{s}}^{{1}/{2}}$. In the later stage of the bridge growth, the bridge evolution again merges with the well-established power-law regime $r\propto {{t}^{{1}/{2}}}$, being either in low or high-viscosity liquids. Moreover, a new inertia-viscous-capillary timescale is proposed, which unifies the combined influence of inertia, viscous, and capillary forces on the evolution of the liquid bridge in liquid environments, highlighting the joint role of inertia and viscous resistance in the coalescence process.

Crafting crystalline topological insulators via accidental mode degeneracies. (arXiv:2312.15529v1 [physics.optics])
Konstantin Rodionenko, Maxim Mazanov, Maxim A. Gorlach

Crystalline topological insulators have recently become a powerful platform for realizing photonic topological states from microwaves to the visible. Appropriate geometric symmetries of the lattice are at the core of their functionality. Here we put forward an alternative approach to craft those systems by designing the internal symmetries of the Hamiltonian via accidental mode degeneracies. We illustrate our approach constructing ananalog of breathing honeycomb lattice using simpler lattice geometry and six times less meta-atoms, reveal edge and corner states and calculate the relevant topological invariants.

Bridging Rokhsar-Kivelson Type and Generic Quantum Phase Transitions via Thermofield Double States. (arXiv:2312.15530v1 [cond-mat.str-el])
Wen-Tao Xu, Rui-Zhen Huang, Guang-Ming Zhang

The formalism of the Rokhsar-Kivelson (RK) model has been frequently used to study topological phase transitions in 2D in terms of the deformed wavefunctions, which are RK-type wavefunctions. A key drawback of the deformed wavefunctions is that the obtained quantum critical points are RK-type, in the sense that the equal-time correlation functions are described by 2D conformal field theories (CFTs). The generic Lorentz invariant quantum critical points described by (2+1)D CFTs can not be obtained from the deformed wavefunctions. To address this issue, we generalize the deformed wavefunction approach to the deformed thermofield double (TFD) state methodology. Through this extension, we can effectively reconstruct the absent temporal dimension at the RK-type quantum critical point. We construct deformed TFD states for a (1+1)D quantum phase transition from a symmetry-protected topological phase to a symmetry-breaking phase, and for generic (2+1)D topological phase transitions from a $\mathbb{Z}_2$ topologically ordered phase to a trivial paramagnetic phase.

Inverse Measurements in Active Nematics. (arXiv:2312.15553v1 [cond-mat.soft])
Aleix Boquet-Pujadas, Jérôme Hardouïn, Junhao Wen, Jordi Ignés-Mullol, Francesc Sagués

We present a framework to take new measurements in nematic systems that contain active elements such as molecular motors. Spatio-temporal fields of stress, velocity, pressure, and forces are obtained jointly from microscopy images. Our inverse-problem approach ensures that they comply with physical laws and are accurate near system boundaries. Our measurements in active biological materials provide new insight for the design of boundary-aware nematic systems. The shear stress unveils a correlation with the nucleation of topological defects. The velocity and pressure fields characterize how boundary effects drive the dynamics of the system in terms of attractors. And the force relates the underlying fluid with the nematic tensor to reveal the activity scales of the system. More broadly, our work establishes a generalizable approach to study experimental systems that are inaccessible to measuring probes.

Relativistic artificial molecules with tunable coupling and orbitals. (arXiv:2312.15570v1 [cond-mat.mes-hall])
Xiao-Feng Zhou, Yu-Chen Zhuang, Mo-Han Zhang, Hao Sheng, Qing-Feng Sun, Lin He

In a molecule formed by two atoms, energy difference between bonding and antibonding orbitals should depend on distance of the two atoms. However, exploring molecular orbitals of two natural atoms with tunable distance has remained an outstanding experimental challenge. Graphene quantum dots (GQDs) can be viewed as relativistic artificial atoms, therefore, offering a unique platform to study molecular physics. Here, through scanning tunneling microscope (STM), we create and directly visualize the formation process of relativistic artificial molecules based on two coupled GQDs with tunable distance. Our study indicates that energy difference between the bonding and antibonding orbitals of the lowest quasibound state increases linearly with inverse distance of the two GQDs due to the relativistic nature of the artificial molecule. For quasibound states with higher orbital momenta, the coupling between these states leads to half-energy spacing of the confined states because the length of the molecular-like orbit is about twice that of the atomic-like orbit. Evolution from ring-like whispering-gallery modes in the artificial atoms to figure-eight orbitals in the artificial molecules is directly imaged. The ability to resolve the coupling and orbitals of the relativistic artificial molecule at the nanoscale level yields insights into the behavior of quantum-relativistic matter.

Field-induced transformation between triangular and square skyrmion crystals in a tetragonal polar magnet. (arXiv:2312.15587v1 [cond-mat.str-el])
Satoru Hayami

Magnetic skyrmions with topologically nontrivial spin textures form a variety of periodic structures depending on microscopic interactions and lattice symmetry. We theoretically investigate a transformation between triangular and square skyrmion crystals against an external magnetic field in a polar tetragonal magnet. By performing the simulated annealing for a classical spin model, we show that the competition of the Dzyaloshinskii-Moriya interaction at multiple wave vectors is a key ingredient in inducing the structural transition in terms of the skyrmion crystals. The present results indicate the importance of magnetic frustration in momentum space as the origin of exotic topological phase transitions.

Planar Hall effect from superconducting fluctuations. (arXiv:2312.15688v1 [cond-mat.supr-con])
L. Attias, K. Michaeli, M. Khodas

We study the planar Hall effect (PHE), and reexamine the Lifshitz invariants in the spin-orbit coupled superconductors. In the Rashba superconductor, the PHE is finite as fluctuations are faster along the applied field than perpendicular to it. We consider spin-orbit splitting that is larger than the critical temperature. In this regime the Cooper pairs are predominantly intra-band. The effective two-band interaction matrix elements are not sensitive enough to the field to affect the PHE. However, in a wide range of parameters this dependence does modify the Lifshitz invariant, linear in field and responsible for the spin diode effect. This contribution is a geometrical effect of the adjustment of the spin texture to the applied field. As such, it also allows the repulsion or attraction in the spin triplet channel to affect the Lifshitz invariant. While the PHE can be studied within the effective two-band superconductor model with an original pairing interaction, the Lifshitz invariant, in general, cannot. Disorder is shown to only moderately suppress the PHE.

Shell-shaped quantum droplet in a three-component ultracold Bose gas. (arXiv:2312.15846v1 [cond-mat.quant-gas])
Yinfeng Ma, Tin-Lun Ho, Xiaoling Cui

We present a scheme to generate shell-shaped droplet in a three-component (1,2,3) ultracold Bose gas. Here binary mixtures (1,2) and (2,3) form quantum droplets due to inter-species attractions, and the two droplets are mutually immiscible due to strong 1-3 repulsion. Importantly, the shared component-2 serves as a glue to link the two droplets together as a globally self-bound object. In this system, the outer droplet naturally develops a shell structure, and its radius and width can be conveniently tuned through the size of core droplet. Moreover, to reach an equilibrium with the shell, the core droplet displays very different spin densities as compared to the vacuum case. These results have been demonstrated in a realistic $^{23}$Na-$^{39}$K-$^{41}$K mixture. Our scheme liberates the shell-shaped Bose gas from stringent conditions with microgravity or fine-tuned traps, and can be readily implemented in cold atoms laboratories on Earth. This paves the way for future exploration of quantum droplets in curved space with non-trivial real-space topologies.

Discovery of a topological exciton insulator with tunable momentum order. (arXiv:2312.15862v1 [cond-mat.str-el])
Md Shafayat Hossain, Tyler A. Cochran, Yu-Xiao Jiang, Songbo Zhang, Huangyu Wu, Xiaoxiong Liu, Xiquan Zheng, Byunghoon Kim, Guangming Cheng, Qi Zhang, Maksim Litskevich, Junyi Zhang, Zi-Jia Cheng, Jinjin Liu, Jia-Xin Yin, Xian P. Yang, Jonathan Denlinger, Massimo Tallarida, Ji Dai, Elio Vescovo, Anil Rajapitamahuni, Hu Miao, Nan Yao, Yingying Peng, Yugui Yao, Zhiwei Wang, Luis Balicas, Titus Neupert, M. Zahid Hasan

Topology and correlations are fundamental concepts in modern physics, but their simultaneous occurrence within a single quantum phase is exceptionally rare. In this study, we present the discovery of such a phase of matter in Ta2Pd3Te5, a semimetal where the Coulomb interaction between electrons and holes leads to the spontaneous formation of excitonic bound states below T=100 K. Our spectroscopy unveils the development of an insulating gap stemming from the condensation of these excitons, thus giving rise to a highly sought-after correlated quantum phase known as the excitonic insulator. Remarkably, our scanning tunneling microscopy measurements reveal the presence of gapless boundary modes in the excitonic insulator state. Their magnetic field response and our theoretical calculations suggest a topological origin of these modes, rendering Ta2Pd3Te5 as the first experimentally identified topological excitonic insulator in a three-dimensional material not masked by any structural phase transition. Furthermore, our study uncovers a secondary excitonic instability below T=5 K, which differs from the primary one in having finite momentum. We observe unprecedented tunability of its wavevector by an external magnetic field. These findings unlock a frontier in the study of novel correlated topological phases of matter and their tunability.

Collisions of Majorana Zero Modes. (arXiv:2312.15878v1 [cond-mat.quant-gas])
Liang-Liang Wang, Wenjun Shao, Jian Li

We investigate the collisions of Majorana zero modes, which are presented as inter-soliton collisional events in fermionic superfluids with spin-orbit coupling. Our results demonstrate that, the zero energy splitting, induced by the overlapping of inter-soliton Majorana wave-functions upon collision, generates an effective repulsive force for Majorana states, which in turn protected themselves against into bulk excitation. As a result, the collision between solitons associated with Majorana zero modes appears to be repulsive and elastic, as they do not penetrate each other but instead repel without energy loss. As well, similar repulsive behavior is observed in collisions between soliton-induced and defect-pinned Majorana zero modes. Our research offers new insights into the features of Majorana fermions, and robustness in the collisions of Majorana zero modes bodes well for the prospects of topological quantum computation with a multitude of Majorana qubits.

Optical absorption tensors based on C$_{70}$ trimers and polymers. (arXiv:2312.15882v1 [cond-mat.mes-hall])
Elnaz Rostampour, Badie Ghavami, Karin Larsson

The optical absorption spectrum of $C_{60}$-dimers and polymers was investigated by Kikuo et al. in 1996\cite{harigaya1996charge}. As a compliment to these earlier studies, the optical absorption spectrum of the $C_{70}$ fullerene has been investigated in the present study. The main purpose was then to compare the absorption spectrum of the $C_{70}$-dimers and trimers and, more specifically, to clarify the effect of these molecular structures on the absorption spectrum. What is most important and decisive is then the value of the conjugation parameter of these $C_{70}$-based molecules. In the present study, a tight-binding model was used in calculating the optical absorption spectra of both $C_{70}$ dimers and polymers, as well as $C_{70}$ trimers and polymers. The change in conjugation parameter for each of these species was found to cause variations in the corresponding optical absorption spectrum. It was found that the absorption tensor of the $C_{70}$ trimer and the polymer was, depending on the value of the conjugation parameters $b=0.5$ and $b=0.8$. The situation was almost the same for the conjugation parameters $b=0.1$ and $b=0.2$. In addition, the value of the band gap was also different depending on the different conjugation parameters, with a reduced value for the larger values of this parameter. As a conclusion, smaller values of the conjugation parameter were not found to have a large effect on the absorption spectrum of the $C_{70}$-dimers and trimers, or in other words, the effect was hardly visible. On the contrary, the larger values caused a drastic change in the optical absorption spectrum of the $C_{70}$-dimers and trimers.

Discovery of acousto-drag photovoltaic effect. (arXiv:2312.15939v1 [cond-mat.mes-hall])
Jiaming Gu, Yicheng Mou, Jianwen Ma, Haonan Chen, Chuanxin Zhang, Yuxiang Wang, Jiayu Wang, Hangwen Guo, Wu Shi, Xiang Yuan, Xue Jiang, Dean Ta, Jian Shen, Cheng Zhang

As a key ingredient in energy harvesting and photodetection, light-to-electricity conversion requires efficient separation of photoexcited electron-hole pairs before recombination. Traditional junction-based mechanisms mainly use build-in electric fields to achieve pair separation and generate photovoltaic effect, which fail to collect photoexcited pairs away from local barrier region. The ability to harvest photovoltaic effect in a homogeneous material upon uniform illumination is appealing, but has only been realized in very few cases such as non-centrosymmetric systems through bulk photovoltaic effect. Here we realize a new type of photovoltaic effect, termed as acousto-drag photovoltaic effect, by travelling surface acoustic waves (t-SAW) in a conventional layered semiconductor MoSe2. Instead of immediately driving the electron-hole pairs to opposite directions after generation, t-SAW induces periodic modulation to electronic bands and drags the photoexcited pairs toward the same travelling direction. The photocurrent can then be extracted by a local barrier, e.g. the metal-semiconductor contact as we used here. By spatially separating the electron-hole generation and extraction processes, the acousto-drag mechanism strongly suppresses charge recombination and yields large nonlocal photoresponse outside the barrier region. We show that when t-SAW is applied, the photoresponse can be enhanced by over two orders of magnitude with exceptionally high external quantum efficiency above 60%. The discovery of acousto-drag photovoltaic effect establishes a new approach towards efficient light-to-electricity conversion without the restriction of crystal symmetry.

Direct observation of topological magnon polarons in a multiferroic material. (arXiv:2312.15943v1 [cond-mat.str-el])
Song Bao, Zhao-Long Gu, Yanyan Shangguan, Zhentao Huang, Junbo Liao, Xiaoxue Zhao, Bo Zhang, Zhao-Yang Dong, Wei Wang, Ryoichi Kajimoto, Mitsutaka Nakamura, Tom Fennell, Shun-Li Yu, Jian-Xin Li, Jinsheng Wen

Magnon polarons are novel elementary excitations possessing hybrid magnonic and phononic signatures, and are responsible for many exotic spintronic and magnonic phenomena. Despite long-term sustained experimental efforts in chasing for magnon polarons, direct spectroscopic evidence of their existence is hardly observed. Here, we report the direct observation of magnon polarons using neutron spectroscopy on a multiferroic Fe$_{2}$Mo$_{3}$O$_{8}$ possessing strong magnon-phonon coupling. Specifically, below the magnetic ordering temperature, a gap opens at the nominal intersection of the original magnon and phonon bands, leading to two separated magnon-polaron bands. Each of the bands undergoes mixing, interconverting and reversing between its magnonic and phononic components. We attribute the formation of magnon polarons to the strong magnon-phonon coupling induced by Dzyaloshinskii-Moriya interaction. Intriguingly, we find that the band-inverted magnon polarons are topologically nontrivial. These results uncover exotic elementary excitations arising from the magnon-phonon coupling, and offer a new route to topological states by considering hybridizations between different types of fundamental excitations.

Gauging of generalized symmetry. (arXiv:2312.15958v1 [cond-mat.str-el])
Tian Lan, Gen Yue, Longye Wang

We give the most general formulation for gauging of generalized symmetry, in terms of the language of higher linear algebra. In short, generalized gauging is just condensation of designated topological operators. Our framework covers all known variants of gauging, and may be used to discover unknown ones. In particular, we proved that gauging is always reversible: the original theory and the gauged theory are Morita equivalent; similarly, the original symmetry and the gauge symmetry are also Morita equivalent.

Perspective on nanoscale magnetic sensors using giant anomalous Hall effect in topological magnetic materials for read head application in magnetic recording. (arXiv:2312.15977v1 [cond-mat.mtrl-sci])
Tomoya Nakatani, Prabhanjan D. Kulkarni, Hirofumi Suto, Keisuke Masuda, Hitoshi Iwasaki, Yuya Sakuraba

Recent advances in the study of materials with topological electronic band structures have revealed magnetic materials exhibiting giant anomalous Hall effects (AHE). The giant AHE has not only attracted the research interest in its mechanism but also opened up the possibility of practical application in magnetic sensors. In this article, we describe simulation-based investigations of AHE magnetic sensors for the applications to read head sensors (readers) of hard disk drives. With the shrinking of magnetic recording patterns, the reader technology, which currently uses multilayer-based tunnel magnetoresistance (TMR) devices, is associated with fundamental challenges, such as insufficient spatial resolution and signal-to-noise ratio (SNR) in sensors with dimensions below 20 nm. The structure of an AHE-based device composed of a single ferromagnetic material is advantageous for magnetic sensors with nanoscale dimensions. We found that AHE readers using topological ferromagnets with giant AHE, such as Co2MnGa, can achieve a higher SNR than current TMR readers. The higher SNR originates from the large output signal of the giant AHE as well as from the reduced thermal magnetic noise, which is the dominant noise in TMR readers. We highlight a major challenge in the development of AHE readers: the reduction in the output signal due to the shunting of the bias current and the leakage of the Hall voltage through the soft magnetic shields surrounding the AHE reader. We propose reader structures that overcome this challenge. Finally, we discuss the scope for future research to realize AHE readers.

Four-dimensional Floquet topological insulator with an emergent second Chern number. (arXiv:2312.16013v1 [cond-mat.mes-hall])
Zheng-Rong Liu, Rui Chen, Bin Zhou

Floquet topological insulators have been widely investigated in lower-dimensional systems. However, Floquet topological insulators in higher-dimensional systems remain unexplored. In this work, we study the effects of time-periodic driving in a four-dimensional (4D) normal insulator, focusing on topological phase transitions at the resonant quasienergy gap. We consider two types of time-periodic driving, including a time-periodic onsite potential and a time-periodic vector potential. We reveal that both types of the time-periodic driving can transform the 4D normal insulator into a 4D Floquet topological insulator characterized by an emergent second Chern number. Moreover, it is found that the topological phase of the 4D system can be modulated by tuning the strength of the time-periodic driving. Our work will be helpful for future investigations on Floquet topological insulators in higher dimensions.

Tensile strain induced brightening of momentum forbidden dark exciton in WS$_2$. (arXiv:2312.16041v1 [cond-mat.mes-hall])
Tamaghna Chowdhury, Sagnik Chatterjee, Dibyasankar Das, Ivan Timokhin, Pablo Díaz Núñez, Gokul M. A., Suman Chatterjee, Kausik Majumdar, Prasenjit Ghosh, Artem Mishchenko, Atikur Rahman

Transition-metal dichalcogenides (TMDs) host tightly bound quasi-particles called excitons. Based on spin and momentum selection rules, these excitons can be either optically bright or dark. In tungsten-based TMDs, momentum-forbidden dark exciton is the energy ground state and therefore it strongly affect the emission properties. In this work, we brighten the momentum forbidden dark exciton by placing WS$_2$ on top of nanotextured substrates which put the WS$_2$ layer under tensile strain, modifying electronic bandstructure. This enables phonon assisted scattering of exciton between momentum valleys, thereby brightening momentum forbidden dark excitons. Our results will pave the way to design ultrasensitive strain sensing devices based on TMDs.

Robust $T$-Linear Resistivity due to SU(4) Valley + Spin Fluctuation Mechanism in Magic Angle Twisted Bilayer Graphene. (arXiv:2312.16042v1 [cond-mat.str-el])
Daisuke Inoue, Seiichiro Onari, Hiroshi Kontani

In the magic angle twisted bilayer graphene (MATBG), non-Fermi liquid like transport phenomena are universally observed. To understand their origin, we perform the self-consistent analysis of the self-energy due to SU(4) valley + spin fluctuations induced by the electron-electron correlation. In the SU(4) fluctuation mechanism, the fifteen channels of fluctuations contribute additively to the self-energy. Therefore, the SU(4) fluctuation mechanism gives much higher electrical resistance than the spin fluctuation mechanism. By the same reason, SU(4) fluctuations of intermediate strength provide $T$-linear resistivity down to $\sim1$K. Interestingly, the $T$-linear resistivity is robustly realizedfor wide range of electron filling, even away from the van-Hove filling. This study provides a strong evidence for the importance of electron-electron correlation in MATBG.

Intrinsic and extrinsic anomalous transport properties in noncollinear antiferromagnetic Mn$_3$Sn from first-principle calculations. (arXiv:2312.16050v1 [cond-mat.mtrl-sci])
Xiuxian Yang, Wanxiang Feng, Xiaodong Zhou, Yuriy Mokrousov, Yugui Yao

Mn$_3$Sn has garnered significant attention due to its kagome lattice, 120$^\circ$ noncollinear antiferromagnetic order, and substantial anomalous Hall effect. In this study, we comprehensively explore intrinsic and extrinsic contributions to anomalous Hall, anomalous Nernst, and anomalous thermal Hall effects, employing first-principle calculations and group theory analysis. Comparative analysis between our theoretical results and available experimental data underscores the predominance of intrinsic mechanism in shaping anomalous transport properties at low temperatures. Specifically, Weyl fermions are identified as the primary contributors to intrinsic anomalous Hall conductivity. The significance of extrinsic mechanisms becomes evident at high temperatures, especially when the longitudinal charge conductivity falls into the dirty regime, where the side jump mechanism plays a vital role. Extrinsic contributions to anomalous transport properties are primarily influenced by the electronic states residing at the Fermi surfaces. Furthermore, anomalous transport properties exhibit periodic variations when subjected to spin rotations within the kagome plane, achievable by applying an external magnetic field. Our findings advance the understanding of anomalous transport phenomena in Mn$_3$Sn and offer insights into potential applications of noncollinear antiferromagnetic materials in spintronics and spin caloritronics.

Ternary Alkali Metal Copper Chalcogenides ACuX (A= Na, K and X= S, Se, Te): Promising Candidate for Solar Harvesting Applications. (arXiv:2312.16063v1 [cond-mat.mtrl-sci])
Gurudayal Behera, Surabhi Suresh Nair, Nirpendra Singh, K. R. Balasubramaniam, Aftab Alam

We report a comprehensive first-principles study of the relative stability of the various possible crystal structures, and the electronic and optical properties of ternary alkali metal chalcogenides ACuX (A= Na/K and X= S/Se/Te) compounds through density functional theory (DFT) calculations. The energetics and phonon spectra of greater than 700 structures were compared, and seven possible stabilized structures of six ACuX compounds were identified using the fixed composition evolutionary search method. Our electronic band structure simulation confirms that all the ternary ACuX compounds are direct band gap semiconductors, with the band gap lying between 0.83 eV to 2.88 eV. These compounds exhibit directly allowed electronic transitions from the valence band to the conduction band, which leads to a significant strength of optical transition probability. This yields a sharp rise in the optical absorption spectra (ranging between 10$^4$ to 10$^5$ cm$^{-1}$) near the energy gap. The estimated spectroscopic limited maximum efficiency (SLME) is about 18% for an 8 $\mu$m thick NaCuTe film. For other ACuX compounds, the SLME ranges between 10% to 13%. In addition, we also explored the feasibility of these ternary ACuX compounds for photocatalytic water splitting applications and found that they can be promising candidates as photocathodes for hydrogen evolution reactions. With a large spread in the band gap and interesting band topology near Fermi level, these chalcogenides can be quite fertile for other energy applications such as thermoelectric, LED, etc.

The nature of low-temperature spin-freezing in frustrated Kitaev magnets. (arXiv:2312.16096v1 [cond-mat.str-el])
U. Jena, P. Khuntia

The subtle interplay between competing degrees of freedom, anisotropy, and spin correlations in frustrated Kitaev quantum materials offer an ideal platform to host myriads of non-trivial quantum states with exotic fractional excitations. The signature of spin-freezing behavior of these spin-orbit driven frustrated magnets is characterized by a bifurcation of zero-field-cooled and field-cooled magnetic susceptibility at low temperatures much below the characteristic interaction energy scale. The magnetic-specific heat exhibits a T^2 dependence below the freezing temperature. The field-independent behavior of magnetic-specific heat below the freezing temperature implies the presence of exotic low-energy excitations. The aging and memory effect experiments in the Kitaev magnets suggest the non-hierarchical free energy distribution, which differs from the hierarchical organization of conventional spin-freezing. Furthermore, NMR spin-lattice relaxation rate follows a power law behavior below the spin-freezing temperature suggesting the persistence of unconventional spin excitation spectra. Herein, we demonstrate that the observed low-temperature spin-freezing phenomena in a few representative Kitaev quantum materials can be effectively explained by the Halperin and Saslow (HS) hydrodynamic modes relevant for non-trivial spin glass materials. The linearly dispersive HS modes are hypothesized to account for instigating non-abelian defect propagation, thereby inducing a spin jam state in the low-temperature regime in frustrated Kitaev magnets. Our investigation reveals that HS modes capture the essence of unconventional spin-freezing ascribed to topological origin in two-dimensional (2D) Kitaev magnets decorated on a honeycomb lattice and its 3D analog hyperhoneycomb that offers a viable ground to extend this framework to a large class of frustrated quantum materials.

Dynamical polarization function, plasmons, their damping and collective effects in semi-Dirac bands. (arXiv:2312.16117v1 [cond-mat.mes-hall])
Gabrielle Ross-Harvey, Andrii Iurov, Liubov Zhemchuzhna, Godfrey Gumbs, Danhong Huang

We have calculated the dynamical polarization, plasmons and damping rates in semi-Dirac bands (SDB's) with zero band gap and half-linear, half-parabolic low-energy spectrum. The obtained plasmon dispersions are strongly anisotropic and demonstrate some crucial features of both two-dimensional electron gas and graphene. Such gapless energy dispersions lead to a localized area of undamped and low-damped plasmons in a limited range of the frequencies and wave vectors. The calculated plasmon branches demonstrate an increase of their energies for a finite tilting of the band structure and a fixed Fermi level which could be used as a signature of a specific tilted spectrum in a semi-Dirac band.

Photoinduced metallic Volkov-Pankratov states in semi-Dirac material. (arXiv:2312.16120v1 [cond-mat.mes-hall])
SK Firoz Islam

We study the emergence of interfacial modes between the two regions of a semi-Dirac type material, which are illuminated by the left and right circularly polarized light, respectively. We show that a smooth boundary between the two regions give rise to an interfacial quantum well which is sensitive to the incoming electron's momentum. The quantum well is found to host the Volkov-Pankratov states which are gapless metallic in nature. Contrary to the inverted mass term, it is the inverted velocity term that induces such states across the boundary. We also note that incident electron can fully pass over the interfacial well without any reflection only at certain light parameters-known as {\it Ramsauer-Townsend} effect. Moreover, we also observe that such modes can even exist across the interface between the irradiated and non-irradiated regions under certain condition.

Magnetic vortex control with current-induced axial magnetization in centrosymmetric Weyl materials. (arXiv:2312.16122v1 [cond-mat.mes-hall])
J. G. Yang, Yaroslav Tserkovnyak, D. A. Pesin

We consider magnetic Weyl metals as a platform to achieve current control of magnetization textures with transport currents, utilizing their underlying band geometry. We show that the transport current in a Weyl semimetal produces an axial magnetization due to orbital magnetic moments of the Weyl electrons. The associated axial magnetization can generate a torque acting on the localized magnetic moments. For the case of a magnetic vortex in a nanodisk of Weyl materials, this current-induced torque can be used to reverse its circulation and polarity. We discuss the axial magnetization torques in Weyl metals on general symmetry grounds, and compare their strength to current-induced torques in more conventional materials.

Large composite fermion effective mass at filling factor 5/2. (arXiv:2312.16135v1 [cond-mat.mes-hall])
M. Petrescu, Z. Berkson-Korenberg, Sujatha Vijayakrishnan, K. W. West, L. N. Pfeiffer, G. Gervais

The 5/2 fractional quantum Hall effect in the second Landau level of extremely clean two-dimensional electron gases has attracted much attention due to its topological order predicted to host quasiparticles that obey non-Abelian quantum statistics and could serve as a basis for fault-tolerant quantum computations. While previous works have establish the Fermi liquid (FL) nature of its putative composite fermion (CF) normal phase, little is known regarding its thermodynamics properties and as a result its effective mass is entirely unknown. Here, we report on time-resolved specific heat measurements at filling factor 5/2, and we examine the ratio of specific heat to temperature as a function of temperature. Combining these specific heat data with existing longitudinal thermopower data measuring the entropy in the clean limit we find that, unless a phase transition/crossover gives rise to large specific heat anomaly, both datasets point towards a large effective mass in the FL phase of CFs at 5/2. We estimate the effective-to-bare mass ratio m*/me to be ranging from ~2 to 4, which is two to three times larger than previously measured values in the first Landau level.

Andreev bound states in superconductor-barrier-superconductor junctions of Rarita-Schwinger-Weyl semimetals. (arXiv:2312.16164v1 [cond-mat.supr-con])
Ipsita Mandal

We consider a superconductor-barrier-superconductor (S-B-S) sandwich configuration built with Rarita-Schwinger-Weyl semimetal featuring four band crossings at a single nodal point. Assuming a homogenous s-wave pairing in each superconducting region, and the barrier region created by applying a voltage of magnitude $V_0 $ across a piece of normal state semimetal, we apply the BdG formalism to compute the discreet energy spectrum $\varepsilon $ of the subgap Andreev bound states in the short-barrier regime. In contrast with the two-band semimetals studied earlier, we find upto four pairs of localized states (rather than one pair for two-band semimetals) in the thin-barrier limit, and each value of $\varepsilon $ has a complicated dependence on the phase difference $\varphi_{12} $ via cosine and sine functions, which cannot be determined analytically. These are artifacts of multiple band crossings hosting quasiparticles of pseudospin value greater than $1/2$. Using the bound state energies, we compute the Josephson current across the junction configuration.

Double and Quadruple Flat Bands tuned by Alternative magnetic Fluxes in Twisted Bilayer Graphene. (arXiv:2210.13976v2 [cond-mat.str-el] UPDATED)
Congcong Le, Qiang Zhang, Cui Fan, Xianxin Wu, Ching-Kai Chiu

Twisted bilayer graphene (TBG) can host the moir\'{e} energy flat bands with two-fold degeneracy serving as a fruitful playground for strong correlations and topological phases. However, the number of degeneracy is not limited to two. Introducing a spatially alternative magnetic field, we report that the induced magnetic phase becomes an additional controllable parameter and leads to an undiscovered generation of four-fold degenerate flat bands. This emergence stems from the band inversion at $\Gamma$ point near the Fermi level with a variation of both twisted angle and magnetic phase. We present the conditions for the emergence of multi-fold degenerate flat bands, which are associated with the eigenvalue degeneracy of a Birman-Schwinger operator. Using holomorphic functions, which explain the origin of the double flat bands in the conventional TBG, we can generate analytical wave functions in the magnetic TBG to show absolute flatness with four-fold degeneracy. Moreover, we identify an orbital-related intervalley coherent state as the many-body ground state at charge neutrality. In contrast, the conventional TBG has only two moir\'{e} energy flat bands, and the highly degenerate flat bands with additional orbital channels in this magnetic platform might bring richer correlation physics.

Multiferroicity and Topology in Twisted Transition Metal Dichalcogenides. (arXiv:2210.14918v3 [cond-mat.str-el] UPDATED)
Ahmed Abouelkomsan, Emil J. Bergholtz, Shubhayu Chatterjee

Van der Waals heterostructures have recently emerged as an exciting platform for investigating the effects of strong electronic correlations, including various forms of magnetic or electrical orders. Here, we perform an unbiased exact diagonalization study of the effects of interactions on topological flat bands of twisted transition metal dichalcogenides (TMDs) at odd integer fillings. For hole-filling $\nu_h = 1$, we find that Chern insulator phases, expected from interaction-induced spin-valley polarization of the bare bands, are quite fragile, and give way to spontaneous multiferroic order -- coexisting ferroelectricity and ferromagnetism, in presence of long-range Coulomb repulsion. We provide a simple real-space picture to understand the phase diagram as a function of interaction range and strength. Our findings establish twisted TMDs as a novel and highly tunable platform for multiferroicity, with potential applications to electrical control of magnetism.

Vibrational and thermal properties of amorphous alumina from first principles. (arXiv:2303.08637v2 [cond-mat.mtrl-sci] UPDATED)
Angela F. Harper, Kamil Iwanowski, William C. Witt, Mike C. Payne, Michele Simoncelli

Amorphous alumina is employed ubiquitously as a high-dielectric-constant material in electronics, and its thermal-transport properties are of key relevance for heat management in electronic chips and devices. Experiments show that the thermal conductivity of alumina depends significantly on the synthesis process, indicating the need for a theoretical study to elucidate the atomistic origin of these variations. Here we employ first-principles simulations to characterize the atomistic structure, vibrational properties, and thermal conductivity of alumina at densities ranging from 2.28 g/cm3 to 3.49 g/cm3. Moreover, using an interatomic potential trained on first-principles data, we investigate how system size affects predictions of the thermal conductivity, showing that simulations containing 120 atoms can already reproduce the bulk limit of the conductivity. Finally, relying on the recently developed Wigner formulation of thermal transport, we shed light on the interplay between atomistic topological disorder and anharmonicity in the context of heat conduction, showing that the former dominates over the latter in determining the conductivity of alumina.

Dynamical criticality of magnetization transfer in integrable spin chains. (arXiv:2303.16691v5 [cond-mat.stat-mech] UPDATED)
Žiga Krajnik, Johannes Schmidt, Enej Ilievski, Tomaž Prosen

Recent studies have found that fluctuations of magnetization transfer in integrable spin chains violate the central limit property. Here we revisit the problem of anomalous counting statistics in the Landau-Lifshitz field theory by specializing to two distinct anomalous regimes featuring a dynamical critical point. By performing optimized numerical simulations using an integrable space-time discretization we extract the algebraic growth exponents of time-dependent cumulants which attain their threshold values. The distinctly non-Gaussian statistics of magnetization transfer in the easy-axis regime is found to converge towards the universal distribution of charged single-file systems. At the isotropic point we infer a weakly non-Gaussian distribution, corroborating the view that superdiffusive spin transport in integrable spin chains does not belong to any known dynamical universality class.

Tuned gap in graphene through laser barrier. (arXiv:2303.17092v2 [cond-mat.mes-hall] UPDATED)
Hasna Chnafa, Miloud Mekkaoui, Ahmed Jellal, Abdelhadi Bahaoui

We study the effect of the energy gap on the transmission of fermions in graphene exposed to linearly polarized light as a laser barrier. We determine the energy spectrum, apply boundary conditions at interfaces, and use the transfer matrix approach to obtain transmissions for all energy modes. We show that when the energy gap increases, the oscillations of transmissions decrease dramatically until they vanish entirely. However, when the barrier width varies, the oscillations become more significant and exhibit sharp peaks. By increasing the incident energy, the laser field suppresses the Fabry-P\'erot resonance, and the transmissions move to the right when the energy gap is tuned.

Role of effective mass anisotropy in realizing a hybrid nodal-line fermion state. (arXiv:2304.13086v3 [cond-mat.mtrl-sci] UPDATED)
Bikash Patra, Rahul Verma, Shin-Ming Huang, Bahadur Singh

Understanding the role of lattice geometry in shaping topological states and their properties is of fundamental importance to condensed matter and device physics. Here we demonstrate how an anisotropic crystal lattice drives a topological hybrid nodal line in transition metal tetraphosphides $Tm$P$_4$ ($Tm$ = Transition metal). $Tm$P$_4$ constitutes a unique class of black phosphorus materials formed by intercalating transition metal ions between the phosphorus layers without destroying the characteristic anisotropic band structure of the black phosphorous. Based on the first-principles calculations and $k \cdot p$ theory, we show that $Tm$P$_4$ harbor a single hybrid nodal line formed between oppositely-oriented anisotropic $Tm~d$ and P states unhinged from the high-symmetry planes. The nodal line consists of both type-I and type-II nodal band crossings whose nature and location are determined by the effective-mass anisotropies of the intersecting bands. We further discuss a possible topological phase transition to exemplify the formation of the hybrid nodal line state in $Tm$P$_4$. Our results offer a comprehensive study for understanding the interplay between structural motifs-driven mass anisotropies and topology in anisotropic lattice materials to realize hybrid semimetal states.

Factors affecting the topological Hall effect in strongly correlated layered magnets: spin of the magnetic atoms, polar and azimuthal angle subtended by the spin texture. (arXiv:2305.13423v3 [cond-mat.mes-hall] UPDATED)
Kaushal Kumar Kesharpu

The Hamiltonian of a two dimensional (2D) magnetic material in the strong correlation regime with a spin texture, for which both azimuthal and polar angle changes, is solved using $su(2)$ path integral method. The dependence of the Chern number on the atomic spin ($S$), azimuthal angle ($\vec{q}_{1}$) and polar angle ($\vec{q}_{2}$) modulation vector of the spin texture on a bipartite honeycomb lattice is found. For $S \leq 3$ it was found that Chern number depends strongly on $\vec{q}_{2}$ and $S$. We discuss applicability of the model to several van der Waals magnets. Experimentally, it is expected that, with increase in spin modulation vector the sign of the topological Hall conductivity changes, $+\sigma_{xy}^{THE} \to -\sigma_{xy}^{THE}$ or vice-versa, when $S$ is constant. We also propose several heterostrucures for experimental realization of this effect.

Transport properties of hybrid single-bilayer graphene interfaces in magnetic field. (arXiv:2305.14284v2 [cond-mat.mes-hall] UPDATED)
Nadia Benlakhouy, Ahmed Jellal, Michael Schreiber

We investigate the electronic properties of a hybrid system that comprises single-bilayer graphene structures subjected to a perpendicular magnetic field. Specifically, our focus is on the behavior exhibited by the zigzag boundaries of the junction, namely Zigzag-1 (ZZ1) and Zigzag-2 (ZZ2), using the continuum Dirac model for rigorous analysis. Our findings reveal a striking dependence of conductance on the width of the bilayer graphene at ZZ1, providing essential insights into the transport behavior of this boundary. Moreover, we observe a captivating phenomenon where the conductance at ZZ2 exhibits prominent maxima, demonstrating a robust correlation with the applied magnetic field. Additionally, our investigation uncovers the profound impact of interfaces on transmission probability, with ZZ1 being notably more affected compared to ZZ2. The variation of the Fermi energy further highlights the significant influence of magnetic field strength on the system's conductive properties, resulting in distinct conductance characteristics between the two regions. The combined results of ZZ1 and ZZ2 provide valuable insights into the system's transport properties. Notably, a clear exponential-like trend in conductance variation with the applied magnetic field underscores the system's strong sensitivity to magnetic changes.

Dynamic structure factor of two-dimensional Fermi superfluid with Rashba spin-orbit coupling. (arXiv:2306.05868v2 [cond-mat.quant-gas] UPDATED)
Huaisong Zhao, Xu Yan, Shi-Guo Peng, Peng Zou

We theoretically calculate the dynamic structure factor of two-dimensional Rashba-type spinorbit coupled (SOC) Fermi superfluid with random phase approximation, and analyse the main characters of dynamical excitation sh own by both density and spin dynamic structure factor during a continuous phase transition between Bardeen-Cooper-Schrieffer superfluid and topological superfluid. Generally we find three different excitations, including collective phonon excitation, two-atom molecular and atomic excitations, and pair-breaking excitations due to two-branch structure of quasi-particle spectrum. It should be emphasized that collective phonon excitation is overlapped with a gapless DD type pair-breaking excitation at the critical Zeeman field hc, and is imparted a finite width to phonon peak when transferred momentum q is around Fermi vector kF. At a much larger transferred momentum (q = 4kF ), the pair-breaking excitation happens earlier than two-atom molecular excitation, which is different from the conventional Fermi superfluid without SOC effect.

Transport properties in gapped graphene through magnetic barrier in a laser field. (arXiv:2307.03999v2 [cond-mat.mes-hall] UPDATED)
Rachid El Aitouni, Miloud Mekkaoui, Ahmed Jellal, Michael Schreiber

We study the transport properties of Dirac fermions through gapped graphene through a magnetic barrier irradiated by a laser field oscillating in time. We use Floquet theory and the solution of Weber's differential equation to determine the energy spectrum corresponding to the three regions composing the system. The boundary conditions and the transfer matrix approach {are} employed to explicitly determine the transmission probabilities for multi-energy bands and the associated conductance. As an illustration, we focus only on the three first bands: the central band $T_0$ (zero photon exchange) and the two first side bands $T_{\pm1}$ (photon emission or absorption). It is found that the laser field activates the process of translation through photon exchange. Furthermore, we show that varying the incident angle and energy gap strongly affects the transmission process. The conductance increases when the number of electrons that cross the barrier increases, namely when there is a significant transmission.

Long-Range Attraction between Graphene and Water/Oil Interfaces. (arXiv:2307.15658v2 [cond-mat.soft] UPDATED)
Avishi Abeywickrama, Douglas H. Adamson, Hannes C. Schniepp

We directly measured the interactions between a hydrophobic solid and a hydrophobic liquid separated by water using force spectroscopy, where colloidal probes were coated with graphene oxide (GO) to interact with immobilized heptane droplets in water. We detected attractions with a long range of ~0.5 microns, which cannot be readily explained by standard Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. When the GO was reduced to become more hydrophobic, these forces increased in strength and ranged up to 1.2 microns, suggesting that the hydrophobic nature of the involved surfaces critically influences the observed long-range forces. Previous studies have addressed such hydrophobic attractions, but were limited to solid/water/solid and solid/water/air scenarios. Here we expand this knowledge to include the solid/water/liquid situation. Based on our results, we propose air bubbles attached to the colloidal probe and molecular rearrangement at the water/oil interface as possible origins of the observed interactions. The proposed mechanism expands insights gained from previous to the solid/water/liquid situation and is universally applicable to describe attractive interactions between hydrophobic bodies of any kind separated by water. Our work will be useful to understand and motivate the formation of many colloid and interface phenomena, including emulsions using 2D materials and other amphiphilic/hydrophobic particles.

First-principle study of spin transport property in $L1_0$-FePd(001)/graphene heterojunction. (arXiv:2308.02171v4 [cond-mat.mtrl-sci] UPDATED)
Hayato Adachi, Ryuusuke Endo, Hikari Shinya, Hiroshi Naganuma, Mitsuharu Uemoto

In our previous work, we synthesized a metal/2D material heterointerface consisting of $L1_0$-ordered iron-palladium (FePd) and graphene (Gr) called FePd(001)/Gr. This system has been explored by both experimental measurements and theoretical calculations. In this study, we focus on a heterojunction composed of FePd and multilayer graphene referred to as FePd(001)/$m$-Gr/FePd(001), where $m$ represents the number of graphene layers. We perform first-principles calculations to predict their spin-dependent transport properties. The quantitative calculations of spin-resolved conductance and magnetoresistance (MR) ratio (150-200%) suggest that the proposed structure can function as a magnetic tunnel junction in spintronics applications. We also find that an increase in $m$ not only reduces conductance but also changes transport properties from the tunneling behavior to the graphite $\pi$-band-like behavior. Additionally, we investigate the spin-transfer torque-induced magnetization switching behavior of our \color{blue} junction structures \color{black} using micromagnetic simulations. Furthermore, we examine the impact of lateral displacements (``sliding'') at the interface and find that the spin transport properties remain robust despite these changes; this is the advantage of two-dimensional material hetero-interfaces over traditional insulating barrier layers such as MgO.

Generalized Majorana edge modes in a number-conserving periodically driven $p$-wave superconductor. (arXiv:2309.01163v2 [cond-mat.mes-hall] UPDATED)
Raditya Weda Bomantara

We study an analytically solvable and experimentally relevant number-conserving periodically driven $p$-wave superconductor. Such a system is found to support generalized Majorana zero and $\pi$ modes which, despite being non-Hermitian, are still capable of encoding qubits. Moreover, appropriate winding numbers characterizing the topology of such generalized Majorana modes are defined and explicitly calculated. We further discuss the fate of the obtained generalized Majorana modes in the presence of finite charging energy. Finally, we shed light on the quantum computing prospects of such modes by demonstrating the robustness of their encoded qubits and explicitly braiding a pair of generalized Majorana modes.

Confinement twists achiral liquid crystals and causes chiral liquid crystals to twist in the opposite handedness: Cases in and around sessile droplets. (arXiv:2309.14242v2 [cond-mat.soft] UPDATED)
Jungmyung Kim, Joonwoo Jeong

We study the chiral symmetry breaking and metastability of confined nematic lyotropic chromonic liquid crystal (LCLC) with and without chiral dopants. The isotropic-nematic coexistence phase of the LCLC renders two confining geometries: sessile isotropic(I) droplets surrounded by the nematic(N) phase and sessile nematic droplets immersed in the isotropic background. In the achiral system with no dopants, LCLC's elastic anisotropy and topological defects induce a spontaneous twist deformation to lower the energetic penalty of splay deformation, resulting in spiral optical textures under crossed polarizers both in the I-in-N and N-in-I systems. While the achiral system exhibits both handednesses with an equal probability, a small amount of the chiral dopant breaks the balance. Notably, in contrast to the homochiral configuration of a chirally doped LCLC in bulk, the spiral texture of the disfavored handedness appears with a finite probability both in the I-in-N and N-in-I systems. We propose director field models explaining how chiral symmetry breaking arises by the energetics and the opposite-twist configurations exist as meta-stable structures in the energy landscape. These findings help us create and control chiral structures using confined LCs with large elastic anisotropy.

Topological interfaces crossed by defects and textures of continuous and discrete point group symmetries in spin-2 Bose-Einstein condensates. (arXiv:2309.17394v2 [cond-mat.quant-gas] UPDATED)
Giuseppe Baio, Matthew T. Wheeler, David S. Hall, Janne Ruostekoski, Magnus O. Borgh

We systematically and analytically construct a set of spinor wave functions representing defects and textures that continuously penetrate interfaces between coexisting, topologically distinct magnetic phases in a spin-2 Bose-Einstein condensate. These include singular and nonsingular vortices carrying mass or spin circulation that connect across interfaces between biaxial- and uniaxial nematic, cyclic and ferromagnetic phases, as well as vortices terminating as monopoles on the interface ("boojums"). The biaxial-nematic and cyclic phases exhibit discrete polytope symmetries featuring non-Abelian vortices and we investigate a pair of non-commuting line defects within the context of a topological interface. By numerical simulations, we characterize the emergence of non-trivial defect core structures, including the formation of composite defects. Our results demonstrate the potential of spin-2 Bose-Einstein condensates as experimentally accessible platforms for exploring interface physics, offering a wealth of combinations of continuous and discrete symmetries.

Majorana Fermion Mean-Field Theories of Kitaev Quantum Spin Liquids. (arXiv:2310.10230v2 [cond-mat.str-el] UPDATED)
Shahnam Ghanbari Saheli, Jennifer Lin, Huanzhi Hu, Frank Krüger

We determine the phase diagrams of anisotropic Kitaev-Heisenberg models on the honeycomb lattice using parton mean-field theories based on different Majorana fermion representations of the $S=1/2$ spin operators. Firstly, we use a two-dimensional Jordan-Wigner transformation (JWT) involving a semi-infinite snake string operator. In order to ensure that the fermionized Hamiltonian remains local we consider the limit of extreme Ising exchange anisotropy in the Heisenberg sector. Secondly, we use the conventional Kitaev representation in terms of four Majorana fermions subject to local constraints, which we enforce through Lagrange multipliers. For both representations we self-consistently decouple the interaction terms in the bond and magnetization channels and determine the phase diagrams as a function of the anisotropy of the Kitaev couplings and the relative strength of the Ising exchange. While both mean-field theories produce identical phase boundaries for the topological phase transition between the gapless and gapped Kitaev quantum spin liquids, the JWT fails to correctly describe the the magnetic instability and finite-temperature behavior. Our results show that the magnetic phase transition is first order at low temperatures but becomes continuous above a certain temperature. At this energy scale we also observe a finite temperature crossover on the quantum spin-liquid side, from a fractionalized paramagnet at low temperatures, in which gapped flux excitations are frozen out, to a conventional paramagnet at high temperatures.

Method of Mechanical Exfoliation of Bismuth with Micro-Trench Structures. (arXiv:2311.01321v2 [cond-mat.mes-hall] UPDATED)
Oulin Yu, Raphaela Allgayer, Simon Godin, Jacob Lalande, Paolo Fossati, Chunwei Hsu, Thomas Szkopek, Guillaume Gervais

The discovery of graphene led to a burst in search for 2D materials originating from layered atomic crystals coupled by van der Waals force. While bulk bismuth crystals share this layered crystal structure, unlike other group V members of the periodic table, its interlayer bonds are stronger such that traditional mechanical cleavage and exfoliation techniques have shown to be inefficient. In this work, we present a novel mechanical cleavage method for exfoliating bismuth by utilizing the stress concentration effect induced by micro-trench SiO2 structures. As a result, the exfoliated bismuth flakes can achieve thicknesses down to the sub-10 nm range which are analyzed by AFM and Raman spectroscopy.

Single-Phase L1$_{0}$-Ordered High Entropy Thin Films with High Magnetic Anisotropy. (arXiv:2311.06618v2 [cond-mat.mtrl-sci] UPDATED)
Willie B. Beeson, Dinesh Bista, Huairuo Zhang, Sergiy Krylyuk, Albert Davydov, Gen Yin, Kai Liu

The vast high entropy alloy (HEA) composition space is promising for discovery of new material phases with unique properties. We explore the potential to achieve rare-earth-free high magnetic anisotropy materials in single-phase HEA thin films. Thin films of FeCoNiMnCu sputtered on thermally oxidized Si/SiO$_{2}$ substrates at room temperature are magnetically soft, with a coercivity on the order of 10 Oe. After post-deposition rapid thermal annealing (RTA), the films exhibit a single face-centered-cubic (fcc) phase, with an almost 40-fold increase in coercivity. Inclusion of 50 at.% Pt in the film leads to ordering of a single L1$_{0}$ high entropy intermetallic phase after RTA, along with high magnetic anisotropy and a 3 orders of magnitude coercivity increase. These results demonstrate a promising HEA approach to achieve high magnetic anisotropy materials using RTA.

Hydrogen Doping Induced $p_x\pm ip_y$ Triplet Superconductivity in Quasi-One-Dimensional K$_2$Cr$_3$As$_3$. (arXiv:2311.10942v2 [cond-mat.supr-con] UPDATED)
Ming Zhang, Chen Lu, Yajiang Chen, Yunbo Zhang, Fan Yang

Quasi-one-dimensional (Q1D) Cr-based pnictide K$_2$Cr$_3$As$_3$ has aroused great research interest due to its possible triplet superconducting pairing symmetry. Recent experiments have shown that incorporating hydrogen atoms into K$_2$Cr$_3$As$_3$ would significantly change its electronic and magnetic properties. Hence, it's necessary to investigate the impact of hydrogen doping in superconducting pairing symmetry of this material. Employing the hydrogen as an non-trivial electron-doping, our calculates show that, different from the $p_z$-wave obtained without hydrogen, the system exhibits $p_x\pm ip_y$ pairing superconductivity under specific hydrogen doping. Specifically, we adopt the random-phase-approximation approach based on a six-band tight-binding model equipped with multi-orbital Hubbard interactions to study the hydrogen-doping dependence of the pairing symmetry and superconducting $T_c$. Under the rigid-band approximation, our pairing phase diagram shows the spin-triplet pairing states is dominated through out the hydrogen-doping regime $x\in (0,0.7)$. Particularly, the $T_c\sim x$ curve shows a peak at the 3D-quasi-1D Lifshitz transition point, and the pairing symmetry around this doping level is $p_x\pm ip_y$. The physical origin of this pairing symmetry is that the density of states is mainly concentrated at $k_x(k_y)$ with large momentum. Due to the three-dimensional character of the real material, this $p_x\pm ip_y$-wave superconducting state possesses point gap nodes. We further provide experiment prediction to identify this triplet $p_x\pm ip_y$-wave superconductivity.

Gauging Non-Invertible Symmetries: Topological Interfaces and Generalized Orbifold Groupoid in 2d QFT. (arXiv:2311.17044v2 [hep-th] UPDATED)
Oleksandr Diatlyk, Conghuan Luo, Yifan Wang, Quinten Weller

Gauging is a powerful operation on symmetries in quantum field theory (QFT), as it connects distinct theories and also reveals hidden structures in a given theory. We initiate a systematic investigation of gauging discrete generalized symmetries in two-dimensional QFT. Such symmetries are described by topological defect lines (TDLs) which obey fusion rules that are non-invertible in general. Despite this seemingly exotic feature, all well-known properties in gauging invertible symmetries carry over to this general setting, which greatly enhances both the scope and the power of gauging. This is established by formulating generalized gauging in terms of topological interfaces between QFTs, which explains the physical picture for the mathematical concept of algebra objects and associated module categories over fusion categories that encapsulate the algebraic properties of generalized symmetries and their gaugings. This perspective also provides simple physical derivations of well-known mathematical theorems in category theory from basic axiomatic properties of QFT in the presence of such interfaces. We discuss a bootstrap-type analysis to classify such topological interfaces and thus the possible generalized gaugings and demonstrate the procedure in concrete examples of fusion categories. Moreover we present a number of examples to illustrate generalized gauging and its properties in concrete conformal field theories (CFTs). In particular, we identify the generalized orbifold groupoid that captures the structure of fusion between topological interfaces (equivalently sequential gaugings) as well as a plethora of new self-dualities in CFTs under generalized gaugings.

Fermionic quartet and vestigial gravity. (arXiv:2312.09435v2 [cond-mat.other] UPDATED)
G.E. Volovik

We discuss the two-step transitions in superconductors, where the intermediate state between the Cooper pair state and the normal metal is the 4-fermion condensate, which is called the intertwined vestigial order. We discuss different types of the vestigial order, which are possible in the spin-triplet superfluid $^3$He, and the topological objects in the vestigial phases. Since in $^3$He the order parameter $A_{\alpha i}$ represents the analog of gravitational tetrads, we suggest that the vestigial states are possible in quantum gravity. As in superconductors, the fermionic vacuum can experience two consequent phase transitions. At first transition the metric appears as the bilinear combination of tetrads $g_{\mu\nu} =\eta_{ab}< \hat E^a_\mu \hat E^b_\nu>$, while the tetrad order parameter is still absent, $e_\mu^a=< \hat E^a_\mu> =0$. This corresponds to the bosonic Einstein general relativity, which emerges in the fermionic vacuum. The nonzero tetrads $e_\mu^a=< \hat E^a_\mu> \neq 0$ appear at the second transition, where a kind of the Einstein-Cartan-Sciama-Kibble tetrad gravity is formed. This suggests that on the levels of particles, gravity acts with different strength on fermions and bosons.

Exposing the odd-parity superconductivity in CeRh$_2$As$_2$ with hydrostatic pressure. (arXiv:2312.09729v3 [cond-mat.supr-con] UPDATED)
Konstantin Semeniuk, Meike Pfeiffer, Javier F. Landaeta, Michael Nicklas, Christoph Geibel, Manuel Brando, Seunghyun Khim, Elena Hassinger

Odd-parity superconductivity is a rare and sought-for state of matter with a potential for applications in topological quantum computing. Crystals with staggered locally non-centrosymmetric structures have been proposed as platforms where a magnetic field can induce a transition between even- and odd-parity superconducting (SC) states. The superconductor CeRh$_2$As$_2$ with a critical temperature $T_{\mathrm{c}}\approx0.4\,\mathrm{K}$ is likely the first example material showing such a phase transition at a magnetic field $\mu_{0}H^{*}=4\,\mathrm{T}$ applied along the crystallographic $c$ axis. CeRh$_2$As$_2$ also undergoes a phase transition of an unknown origin at $T_{0}=0.5\,\mathrm{K}$ and presents signs of an antiferromagnetism below $0.25\,\mathrm{K}$. Under a hydrostatic pressure of $P_0\approx0.5\,\mathrm{GPa}$, the $T_{0}$ order vanishes, resulting in a quantum critical point. Here, using resistivity measurements under pressure, we investigate how the correlations and normal-state orders affect the SC phase switching. We find an enhancement of the in-plane critical field near $P_0$. At the same time, the two SC states persist well past $P_{0}$, until at least $2.7\,\mathrm{GPa}$ and $H^{*}$ is reduced to $0.3\,\mathrm{T}$, making the putative odd-parity state stable almost down to zero field.

A solvable two-dimensional swarmalator model. (arXiv:2312.10178v2 [nlin.AO] UPDATED)
Kevin O'Keeffe, Gourab Kumar Sar, Md Sayeed Anwar, Joao U. F. Lizárraga, Marcus A. M. de Aguiar, Dibakar Ghosh

Swarmalators are oscillators that swarm through space as they synchronize in time. Introduced a few years ago to model many systems which mix synchrony with self-assembly, they remain poorly understood theoretically. Here we obtain the first analytic results on swarmalators moving in two-dimensional (2D) plane by enforcing periodic boundary conditions; this simpler topology allows expressions for order parameters, stabilities, and bifurcations to be derived exactly. We suggest some future directions for swarmalator research and point out some connections to the Kuramoto model and the Vicsek model from active matter; these are intended as a call-to-arms for the sync community and other researchers looking for new problems and puzzles to work on.

Extracting topological orders of generalized Pauli stabilizer codes in two dimensions. (arXiv:2312.11170v2 [quant-ph] UPDATED)
Zijian Liang, Yijia Xu, Joseph T. Iosue, Yu-An Chen

In this paper, we introduce an algorithm for extracting topological data from translation invariant generalized Pauli stabilizer codes in two-dimensional systems, focusing on the analysis of anyon excitations and string operators. The algorithm applies to $\mathbb{Z}_d$ qudits, including instances where $d$ is a nonprime number. This capability allows the identification of topological orders that may differ from $\mathbb{Z}_d$ toric codes, thereby extending the scope beyond the established theorem that Pauli stabilizer codes of $\mathbb{Z}_p$ qudits (with $p$ being a prime) are equivalent to finite copies of $\mathbb{Z}_p$ toric codes and trivial stabilizers. The algorithm is designed to determine all anyons and their string operators, enabling the computation of their fusion rules, topological spins, and braiding statistics. The method converts the identification of topological orders into computational tasks, including Gaussian elimination, the Hermite normal form, and the Smith normal form of truncated Laurent polynomials. Furthermore, the algorithm provides a systematic approach for studying quantum error-correcting codes. We apply it to various codes, such as self-dual CSS quantum codes modified from the color code and non-CSS quantum codes that contain the double semion topological order or the six-semion topological order.

Family Puzzle, Framing Topology, $c_-=24$ and 3(E8)$_1$ Conformal Field Theories: 48/16 = 45/15 = 24/8 =3. (arXiv:2312.14928v1 [hep-th] CROSS LISTED)
Juven Wang

Family Puzzle or Generation Problem demands an explanation of why there are 3 families or generations of quarks and leptons in the Standard Model of particle physics. Here we propose a novel solution -- the multiple of 3 families of 16 Weyl fermions (namely $(N_f=3) \times 16$) in the 3+1d spacetime dimensions are topologically robust due to constraints rooted in profound mathematics (such as Hirzebruch signature and Rokhlin theorems, and cobordism) and derivable in physics (such as chiral edge states, quantized thermal Hall conductance, and gravitational Chern-Simons theory), which holds true even forgetting or getting rid of any global symmetry or gauge structure of the Standard Model. By the dimensional reduction through a sequence of sign-reversing mass domain wall of domain wall and so on, we reduce the Standard Model fermions to obtain the $(N_f=3) \times 16$ multiple of 1+1d Majorana-Weyl fermion with a total chiral central charge $c_-=24$. Effectively via the fermionization-bosonization, the 1+1d theory becomes 3 copies of $c_-=8$ of (E$_8)_1$ conformal field theory, living on the boundary of 3 copies of 2+1d E$_8$ quantum Hall states. Based on the framing anomaly-free $c_- = 0 \mod 24$ modular invariance, the framed bordism and string bordism $\mathbb{Z}_{24}$ class, the 2-framing and $p_1$-structure, the $w_1$-$p_1$ bordism $\mathbb{Z}_3$ class constraints, we derive the family number constraint $N_f \in (\frac{48}{16} =\frac{24}{8}=3) \mathbb{Z}$. The dimensional reduction process, although not necessary, is sufficiently supported by the $\mathbb{Z}_{16}$ class Smith homomorphism. We also comment on the $\frac{45}{15}=3$ relation: the 3 families of 15 Weyl-fermion Standard Model vacuum where the absence of some sterile right-handed neutrinos is fulfilled by additional topological field theories or conformal field theories in Ultra Unification.

Found 5 papers in prb
Date of feed: Wed, 27 Dec 2023 04:16:57 GMT

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)|(flatband)|(flat.{1}band)|(LK.{1}99)

Nonequilibrium dynamics of bosons with dipole symmetry: Large-$N$ Keldysh approach
Md Mursalin Islam, K. Sengupta, and Rajdeep Sensarma
Author(s): Md Mursalin Islam, K. Sengupta, and Rajdeep Sensarma

We study the quench and the ramp dynamics of interacting $N$-component charged bosons with dipole symmetry using Schwinger-Keldysh field theory in the large-$N$ limit. The equilibrium phase diagram of these bosons shows two phases in the large-$N$ limit. The first is a normal phase where both the gl…

[Phys. Rev. B 108, 214314] Published Tue Dec 26, 2023

Quantum Weyl-Heisenberg antiferromagnet
Peter Rosenberg and Efstratios Manousakis
Author(s): Peter Rosenberg and Efstratios Manousakis

Beginning from the conventional square-lattice nearest-neighbor antiferromagnetic Heisenberg model, we allow the ${J}_{x}$ and ${J}_{y}$ couplings to be anisotropic, with their values depending on the bond orientation. The emergence of anisotropic, bond-dependent couplings should be expected to occu…

[Phys. Rev. B 108, 214431] Published Tue Dec 26, 2023

Moiré superstructures in marginally twisted ${\mathrm{NbSe}}_{2}$ bilayers
James G. McHugh, Vladimir V. Enaldiev, and Vladimir I. Fal'ko
Author(s): James G. McHugh, Vladimir V. Enaldiev, and Vladimir I. Fal'ko

The creation of moiré superlattices in twisted bilayers of two-dimensional crystals has been utilized to engineer quantum material properties in graphene and transition metal dichalcogenide semiconductors. Here, we examine the structural relaxation and electronic properties in small-angle twisted bi…

[Phys. Rev. B 108, 224111] Published Tue Dec 26, 2023

Nematic order in topological Sachdev-Ye-Kitaev models
Andrew Hardy, Anjishnu Bose, and Arun Paramekanti
Author(s): Andrew Hardy, Anjishnu Bose, and Arun Paramekanti

We study a class of multiorbital models based on those proposed by Venderbos et al. [Phys. Rev. B 98, 235160 (2018)] which exhibit an interplay of topology, interactions, and fermion incoherence. In the noninteracting limit, these models exhibit trivial and Chern insulator phases with Chern number $…

[Phys. Rev. B 108, 235169] Published Tue Dec 26, 2023

Complete topological phase diagram and realization of minimum Weyl nodes in a sheared chiral crystal of elemental tellurium
Shuai Fan, Botao Fu, Da-Shuai Ma, and Rui Wang
Author(s): Shuai Fan, Botao Fu, Da-Shuai Ma, and Rui Wang

Ideal Weyl semimetals, with minimum Weyl nodes located far away from each other in reciprocal space and near the Fermi level in the energy space, are considered to be crucial for revealing the intrinsic physical properties of Weyl semimetals. Based on first-principles calculations, we demonstrate th…

[Phys. Rev. B 108, 235211] Published Tue Dec 26, 2023

Found 2 papers in prl
Date of feed: Wed, 27 Dec 2023 04:16:54 GMT

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)|(flatband)|(flat.{1}band)|(LK.{1}99)

Accurate Determination of Blackbody Radiation Shifts in a Strontium Molecular Lattice Clock
B. Iritani, E. Tiberi, W. Skomorowski, R. Moszynski, M. Borkowski, and T. Zelevinsky
Author(s): B. Iritani, E. Tiberi, W. Skomorowski, R. Moszynski, M. Borkowski, and T. Zelevinsky

Molecular lattice clocks enable the search for new physics, such as fifth forces or temporal variations of fundamental constants, in a manner complementary to atomic clocks. Blackbody radiation (BBR) is a major contributor to the systematic error budget of conventional atomic clocks and is notorious…

[Phys. Rev. Lett. 131, 263201] Published Tue Dec 26, 2023

Twistronics of Kekulé Graphene: Honeycomb and Kagome Flat Bands
Michael G. Scheer and Biao Lian
Author(s): Michael G. Scheer and Biao Lian

Kekulé-O order in graphene, which has recently been realized experimentally, induces Dirac electron masses on the order of $m∼100\text{ }\text{ }\mathrm{meV}$. We show that twisted bilayer graphene in which one or both layers have Kekulé-O order exhibits nontrivial flat electronic bands on honeycomb…

[Phys. Rev. Lett. 131, 266501] Published Tue Dec 26, 2023

Found 1 papers in prx
Date of feed: Wed, 27 Dec 2023 04:16:55 GMT

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)|(flatband)|(flat.{1}band)|(LK.{1}99)

Bogoliubov Excitations Driven by Thermal Lattice Phonons in a Quantum Fluid of Light
Irénée Frérot, Amit Vashisht, Martina Morassi, Aristide Lemaître, Sylvain Ravets, Jacqueline Bloch, Anna Minguzzi, and Maxime Richard
Author(s): Irénée Frérot, Amit Vashisht, Martina Morassi, Aristide Lemaître, Sylvain Ravets, Jacqueline Bloch, Anna Minguzzi, and Maxime Richard

Quantum fluids of light are coupled to their environments. A joint theory-experiment analysis shows this environment includes the thermal vibrations of the lattice hosting the fluid.

[Phys. Rev. X 13, 041058] Published Tue Dec 26, 2023

Found 3 papers in pr_res
Date of feed: Wed, 27 Dec 2023 04:16:55 GMT

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)|(flatband)|(flat.{1}band)|(LK.{1}99)

Photon vortex generation by synchrotron radiation experiments in relativistic quantum approach
Tomoyuki Maruyama, Takehito Hayakawa, Ryoichi Hajima, Toshitaka Kajino, and Myung-Ki Cheoun
Author(s): Tomoyuki Maruyama, Takehito Hayakawa, Ryoichi Hajima, Toshitaka Kajino, and Myung-Ki Cheoun

We formulate a theoretical approach to describe photon vortex production in synchrotron/cyclotron radiation from a helical moving electron under a uniform magnetic field in the relativistic quantum framework. In quantum theory, electron orbitals in a magnetic field are under Landau states. The Landa…

[Phys. Rev. Research 5, 043289] Published Tue Dec 26, 2023

Polarity-dependent twist-controlled resonant tunneling device based on few-layer $\mathrm{W}{\mathrm{Se}}_{2}$
Kei Kinoshita, Rai Moriya, Shota Okazaki, Yijin Zhang, Satoru Masubuchi, Kenji Watanabe, Takashi Taniguchi, Takao Sasagawa, and Tomoki Machida
Author(s): Kei Kinoshita, Rai Moriya, Shota Okazaki, Yijin Zhang, Satoru Masubuchi, Kenji Watanabe, Takashi Taniguchi, Takao Sasagawa, and Tomoki Machida

Few-layer (FL) transition metal dichalcogenides have been found to exhibit discrete subbands, called van der Waals quantum well (vdWQW) states, resulting from out-of-plane quantum confinement. In this study, we reveal the twisted-resonant tunneling characteristics of a vdWQW device using a three-lay…

[Phys. Rev. Research 5, 043292] Published Tue Dec 26, 2023

Propagation effects of seeded collective emission by two-photon excited oxygen atoms
Xin Wang, Yu-Hung Kuan, Jun Jie Cui, Yu Kun Yang, Fan Xing, Wen-Te Liao, Luqi Yuan, Yongjun Cheng, Zeyang Liao, Zheng Li, and Song Bin Zhang
Author(s): Xin Wang, Yu-Hung Kuan, Jun Jie Cui, Yu Kun Yang, Fan Xing, Wen-Te Liao, Luqi Yuan, Yongjun Cheng, Zeyang Liao, Zheng Li, and Song Bin Zhang

A strong ultraviolet pumping laser propagating through the atmosphere could activate the medium and produce the forward and backward coherent air lasing. In this work, we present the theoretical analyses of forward and backward lasing dynamics in the long gain medium consisting of oxygen atoms. By n…

[Phys. Rev. Research 5, 043293] Published Tue Dec 26, 2023