Found 43 papers in cond-mat
Date of feed: Wed, 10 Jan 2024 01:30:00 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)

"Quantum Geometric Nesting'' and Solvable Model Flat-Band Systems. (arXiv:2401.04163v1 [cond-mat.str-el])
Zhaoyu Han, Jonah Herzog-Arbeitman, B. Andrei Bernevig, Steven A. Kivelson

We introduce the concept of ``quantum geometric nesting'' (QGN) to characterize the idealized ordering tendencies of certain flat-band systems implicit in the geometric structure of the flat-band subspace. Perfect QGN implies the existence of an infinite class of local interactions that can be explicitly constructed and give rise to solvable ground states with various forms of possible fermion bi-linear order, including flavor ferromagnetism, density waves, and superconductivity. For the ideal Hamiltonians constructed in this way, we show that certain aspects of the low-energy spectrum can also be exactly computed including, in the superconducting case, the phase stiffness. Examples of perfect QGN include flat bands with certain symmetries (e.g. chiral or time-reversal), and non-symmetry-related cases exemplified with an engineered model for pair-density-wave. Extending this approach, we obtain exact superconducting ground states with nontrivial pairing symmetry.

The Odd Fermion. (arXiv:2401.04223v1 [hep-th])
Daniel S. Freed, Michael J. Hopkins, Constantin Teleman

In this short note we use the geometric approach to (topological) field theory to address the question: Does an odd number of quantum mechanical fermions make sense?

Electron quantum optics in graphene. (arXiv:2401.04233v1 [cond-mat.mes-hall])
Himadri Chakraborti, Cosimo Gorini, Angelika Knothe, Ming-Hao Liu, Péter Makk, Francois D. Parmentier, David Perconte, Klaus Richter, Preden Roulleau, Benjamin Sacépé, Christian Schönenberger, Wenmin Yang

In the last decade, graphene has become an exciting platform for electron optical experiments, in many aspects superior to conventional two-dimensional electron gases (2DEGs). A major advantage, besides the ultra-large mobilities, is the fine control over the electrostatics, which gives the possibility of realising gap-less and compact p-n interfaces with high precision. The latter host non-trivial states, \eg, snake states in moderate magnetic fields, and serve as building blocks of complex electron interferometers. Thanks to the Dirac spectrum and its non-trivial Berry phase, the internal (valley and sublattice) degrees of freedom, and the possibility to tailor the band structure using proximity effects, such interferometers open up a completely new playground based on novel device architectures. In this review, we introduce the theoretical background of graphene electron optics, fabrication methods used to realise electron-optical devices, and techniques for corresponding numerical simulations. Based on this, we give a comprehensive review of ballistic transport experiments and simple building blocks of electron optical devices both in single and bilayer graphene, highlighting the novel physics that is brought in compared to conventional 2DEGs. After describing the different magnetic field regimes in graphene p-n junctions and nanostructures, we conclude by discussing the state of the art in graphene-based Mach-Zender and Fabry-Perot interferometers.

Shear deformation in CuZr metallic glass: A statistical and complex network analysis. (arXiv:2401.04252v1 [cond-mat.mtrl-sci])
Fernando Corvacho, Victor Muñoz, Matias Sepulveda-Macias, Gonzalo Gutierrez

We have implemented a complex network description for metallic glasses, able to predict the elasto-plastic regime, the location of shear bands and the statistics that controls the plastic events that originate in the material due to a deformation process. By means of molecular dynamics simulations, we perform a shear deformation test, obtaining the stress-strain curve for CuZr metallic glass samples. The atomic configurations of the metallic glass are mapped to a graph, where a node represents an atom whose stress/strain is above a certain threshold, and edges are connections between existing nodes at consecutive timesteps in the simulation. We made a statistical study of some physical descriptors such as shear stress, shear strain, volumetric strain and non-affine displacement to use them as construction tools for complex networks. We have calculated their probability density functions, skewness, kurtosis and gini coefficient to analyze the inequality of the distributions. We study the evolution of the resulting complex network, by computing topological metrics such as degree, clustering coefficient, betweenness and closeness centrality as a function of the strain. We have obtained correlations between the physical phenomena produced by the deformation with the data recorded by these metrics. By means the visual representation of the networks, we have also found direct correlations between metrics and the local atomic shear strain, so that they are able to predict the location of shear bands, as well as the formation of highly connected and interacting communities, which we interpret as shear transformation zones. Our results suggest that the complex network approach has interesting capabilities for the description of mechanical properties of metallic glasses.

Flexible thermoelectrics in crossed graphene/hBN composites. (arXiv:2401.04274v1 [cond-mat.mtrl-sci])
M.Amir Bazrafshan, Farhad Khoeini

Nanostructures exhibit unusual properties due to the dominance of quantum mechanical effects. In addition, the geometry of a nanostructure can have a strong influence on its physical properties. Using the tight-binding (TB) and force-constant (FC) approaches with the help of the non-equilibrium Green's function (NEGF) method, the transport and thermoelectric properties of cross-shaped (X-shaped) composite heterostructures are studied in two cases: Mixed graphene and h-BN (HETX-CBN) and all graphene (HETX-C) cross-shaped structures. Our numerical results show that an X-shaped structure helps to manipulate its electronic and phononic properties. The transport energy gap can be tuned in the range of ~0.8 eV by changing one arm width. Due to the drastic decrease in the electronic conductance of HETX-CBN and the dominance of the phononic thermal conductance, the ZT performance is degraded despite the high S value (in the order of meV). However, HETX-C has better ZT performance due to better electronic conductance and lower phononic/electronic thermal ratio, it can enhance the ZT ~2.5 times compared to that of zigzag graphene nanoribbon. The thermoelectric properties of the system can be tuned by controlling the size of the arms of the device and the type of its atoms.

Revisiting the Landau criterion: a hydrodynamic and holographic approach to superfluid instabilities. (arXiv:2401.04275v1 [hep-th])
Filippo Sottovia

In this thesis we investigate the instabilities of superfluids at finite superflow by means of a hydrodynamical approach. We find that at a finite value of the background superfluid velocity a hydrodynamic collective mode crosses to the upper half complex frequency plane, thereby signalling a dynamical instability. At the same time, however, this instability is also thermodynamic, as its onset is controlled by one of the second derivatives of the free energy changing sign. We carry out our analysis in two main setups: the "probe limit", where the fluctuations of the temperature and the normal fluid's velocity are frozen, and a complete approach, which includes them. In both cases we test our results with the help of gauge-gravity duality, finding good agreement between the hydrodynamic modes of the boundary theory and the quasinormal modes of the gravity theory. Our criterion for the onset of the instability, which is formulated in a model-independent way, applies to interacting systems irrespective of the strength of interactions, does not rely on boost invariance and does not assume any specific quantum statistics. As a final check, we also show that it yields the Landau critical velocity for Galilean superfluids with Bose-Einstein quasiparticles.

New twisted van der Waals fabrication method based on strongly adhesive polymer. (arXiv:2401.04313v1 [cond-mat.mtrl-sci])
Giung Park, Suhan Son, Jongchan Kim, Yunyeong Chang, Kaixuan Zhang, Miyoung Kim, Jieun Lee, Je-Geun Park

Observations of emergent quantum phases in twisted bilayer graphene prompted a flurry of activities in van-der-Waals (vdW) materials beyond graphene. Most current twisted experiments use a so-called tear-and-stack method using a polymer called PPC. However, despite the clear advantage of the current PPC tear-and-stack method, there are also technical limitations, mainly a limited number of vdW materials that can be studied using this PPC-based method. This technical bottleneck has been preventing further development of the exciting field beyond a few available vdW samples. To overcome this challenge and facilitate future expansion, we developed a new tear-and-stack method using a strongly adhesive polycaprolactone (PCL). With similar angular accuracy, our technology allows fabrication without a capping layer, facilitating surface analysis and ensuring inherently clean interfaces and low operating temperatures. More importantly, it can be applied to many other vdW materials that have remained inaccessible with the PPC-based method. We present our results on twist homostructures made with a wide choice of vdW materials - from two well-studied vdW materials (graphene and MoS$_2$) to the first-ever demonstrations of other vdW materials (NbSe$_2$, NiPS$_3$, and Fe$_3$GeTe$_2$). Therefore, our new technique will help expand $moir\acute{e}$ physics beyond few selected vdW materials and open up more exciting developments.

Gate-tunable topological phases in superlattice modulated bilayer graphene. (arXiv:2401.04321v1 [cond-mat.mes-hall])
Yongxin Zeng, Tobias M. R. Wolf, Chunli Huang, Nemin Wei, Sayed Ali Akbar Ghorashi, Allan H. MacDonald, Jennifer Cano

Superlattice potential modulation can produce flat minibands in Bernal-stacked bilayer graphene. In this work we study how band topology and interaction-induced symmetry-broken phases in this system are controlled by tuning the displacement field and the shape and strength of the superlattice potential. We use an analytic perturbative analysis to demonstrate that topological flat bands are favored by a honeycomb-lattice-shaped potential, and numerics to show that the robustness of topological bands depends on both the displacement field strength and the periodicity of the superlattice potential. At integer fillings of the topological flat bands, the strength of the displacement field and the superlattice potential tune phase transitions between quantum anomalous Hall insulator, trivial insulator, and metallic states. We present mean-field phase diagrams in a gate voltage parameter space at filling factor $\nu=1$, and discuss the prospects of realizing quantum anomalous Hall insulators and fractional Chern insulators when the superlattice potential modulation is produced by dielectric patterning or adjacent moir\'e materials.

Long-lived topological time-crystalline order on a quantum processor. (arXiv:2401.04333v1 [quant-ph])
Liang Xiang, Wenjie Jiang, Zehang Bao, Zixuan Song, Shibo Xu, Ke Wang, Jiachen Chen, Feitong Jin, Xuhao Zhu, Zitian Zhu, Fanhao Shen, Ning Wang, Chuanyu Zhang, Yaozu Wu, Yiren Zou, Jiarun Zhong, Zhengyi Cui, Aosai Zhang, Ziqi Tan, Tingting Li, Yu Gao, Jinfeng Deng, Xu Zhang, Hang Dong, Pengfei Zhang, Si Jiang, Weikang Li, Zhide Lu, Zheng-Zhi Sun, Hekang Li, Zhen Wang, Chao Song, Qiujiang Guo, Fangli Liu, Zhe-Xuan Gong, Alexey V. Gorshkov, Norman Y. Yao, Thomas Iadecola, Francisco Machado, H. Wang, Dong-Ling Deng

Topologically ordered phases of matter elude Landau's symmetry-breaking theory, featuring a variety of intriguing properties such as long-range entanglement and intrinsic robustness against local perturbations. Their extension to periodically driven systems gives rise to exotic new phenomena that are forbidden in thermal equilibrium. Here, we report the observation of signatures of such a phenomenon -- a prethermal topologically ordered time crystal -- with programmable superconducting qubits arranged on a square lattice. By periodically driving the superconducting qubits with a surface-code Hamiltonian, we observe discrete time-translation symmetry breaking dynamics that is only manifested in the subharmonic temporal response of nonlocal logical operators. We further connect the observed dynamics to the underlying topological order by measuring a nonzero topological entanglement entropy and studying its subsequent dynamics. Our results demonstrate the potential to explore exotic topologically ordered nonequilibrium phases of matter with noisy intermediate-scale quantum processors.

Kibble-Zurek scalings and coarsening laws in slowly quenched classical Ising chains. (arXiv:2401.04342v1 [cond-mat.stat-mech])
Lakshita Jindal, Kavita Jain

We consider a one-dimensional classical ferromagnetic Ising model when it is quenched from a low temperature to zero temperature in finite time using Glauber or Kawasaki dynamics. Most of the previous work on finite-time quenches assume that the system is initially in equilibrium and focus on the excess defect density at the end of the quench which decays algebraically in quench time with Kibble-Zurek exponent. Here we are interested in understanding the conditions under which the Kibble-Zurek scalings do not hold and in elucidating the full dynamics of the defect density. We find that depending on the initial conditions and quench time, the dynamics of the defect density can be characterized by coarsening and/or the standard finite-time quench dynamics involving adiabatic evolution and Kibble-Zurek dynamics; the time scales for crossover between these dynamical phases are determined by coarsening time and stationary state relaxation time. As a consequence, the defect density at the end of the quench is either a constant or decays following coarsening laws or Kibble-Zurek scaling. For the Glauber chain, we formulate a low temperature scaling theory and find exact expressions for the final defect density for various initial conditions. For the Kawasaki chain where the dynamic exponents for coarsening and stationary state dynamics are different, we verify the above findings numerically and also examine the effect of unequal dynamic exponents.

Controlling chaos: Periodic defect braiding in active nematics confined to a cardioid. (arXiv:2401.04363v1 [cond-mat.soft])
Fereshteh L. Memarian, Derek Hammar, Md Mainul Hasan Sabbir, Mark Elias, Kevin A. Mitchell, Linda Hirst

This work examines self-mixing in active nematics, a class of fluids in which mobile topological defects drive chaotic flows in a system comprised of biological filaments and molecular motors. We present experiments that demonstrate how geometrical confinement can influence the braiding dynamics of the defects. Notably, we show that confinement in cardioid-shaped wells leads to realization of the golden braid, a maximally efficient mixing state of exactly three defects with no defect creation or annihilation. We characterize the golden braid state using different measures of topological entropy and the Lyapunov exponent. In particular, topological entropy measured from the stretching rate of material lines agrees well with an analytical computation from braid theory. Increasing the size of the confining cardioid produces a transition from the golden braid, to the fully chaotic active turbulent state.

Characterization of two fast-turnaround dry dilution refrigerators for scanning probe microscopy. (arXiv:2401.04373v1 [cond-mat.mes-hall])
Mark E. Barber, Yifan Li, Jared Gibson, Jiachen Yu, Zhanzhi Jiang, Yuwen Hu, Zhurun Ji, Nabhanila Nandi, Jesse C. Hoke, Logan Bishop-Van Horn, Gilbert R. Arias, Dale J. Van Harlingen, Kathryn A. Moler, Zhi-Xun Shen, Angela Kou, Benjamin E. Feldman

Low-temperature scanning probe microscopes (SPMs) are critical for the study of quantum materials and quantum information science. Due to the rising costs of helium, cryogen-free cryostats have become increasingly desirable. However, they typically suffer from comparatively worse vibrations than cryogen-based systems, necessitating the understanding and mitigation of vibrations for SPM applications. Here we demonstrate the construction of two cryogen-free dilution refrigerator SPMs with minimal modifications to the factory default and we systematically characterize their vibrational performance. We measure the absolute vibrations at the microscope stage with geophones, and use both microwave impedance microscopy and a scanning single electron transistor to independently measure tip-sample vibrations. Additionally, we implement customized filtering and thermal anchoring schemes, and characterize the cooling power at the scanning stage and the tip electron temperature. This work serves as a reference to researchers interested in cryogen-free SPMs, as such characterization is not standardized in the literature or available from manufacturers.

Spin current leakage and Onsager reciprocity in interfacial spin-charge interconversion. (arXiv:2401.04413v1 [cond-mat.mes-hall])
Aurelien Manchon, Shuyuan Shi, Hyunsoo Yang

Experimental investigations of spin-charge interconversion in magnetic bilayers comprising a ferromagnet adjacent to a topological insulator have reported scattered results on the spin-charge and charge-spin conversion efficiency. Attempting to reconcile these contradicting experimental results, we develop a phenomenological theory of spin-charge interconversion accounting for both interfacial interconversion through the spin galvanic effect, also called the Rashba-Edelstein effect, as well as bulk interconversion via the spin Hall effect. We find that the spin current leakage into the nonmagnetic metal plays a central role during the spin-to-charge and charge-to-spin conversion, leading to dissymmetric interconversion processes. In particular, spin-to-charge conversion is much less sensitive to the spin current absorption in the nonmagnetic metal than charge-to-spin conversion. This suggests that spin pumping is a more trustable technique to extract the interfacial Rashba parameter than spin-orbit torque.

Band Geometry Induced High-Angular Momentum Excitonic Superfluid in Gapped Chiral Fermion Systems. (arXiv:2401.04416v1 [cond-mat.mes-hall])
Huaiyuan Yang, Yuelin Shao, Xi Dai, Xin-Zheng Li

We study the exciton condensation in the heterostructures where the electron layer and hole layer formed by gapped chiral Fermion (GCF) systems are separately gated. High-angular momentum such as p- and d-wave like excitonic pairing may emerge when the gap of the GCF systems is small compared to the Fermi energy, and the chiral winding number of the electrons and holes are the same. This is a result of the non-trivial band geometry and can be linked to the Berry curvature when projected onto the Fermi surface. In realistic systems, we propose that staggered graphene and magnetic topological surface states are promising candidates for realizing p-wave exciton superfluid, and anomalous Hall conductivity can be used as a signature in experiments.

Disorder-induced topological superconductivity in a spherical quantum-Hall--superconductor hybrid. (arXiv:2401.04426v1 [cond-mat.mes-hall])
Koji Kudo, Ryota Nakai, Kentaro Nomura

Quantum-Hall--Superconductor hybrids have been predicted to exhibit various types of topological order, providing possible platforms for intrinsically fault-tolerant quantum computing. In this paper, we develop a formulation to construct this hybrid system on a sphere, a useful geometry for identifying topologically ordered states due to its compact and contractible nature. As a preliminary step using this framework, we investigate disorder effects on the Rashba-coupled quantum Hall system combined with the type-II superconductor. By diagonalizing the BdG Hamiltonian projected into a Rashba-coupled Landau level, we demonstrate the emergence of a topological superconducting phase resulting from disorders and proximity-induced pairing. Distinctive gapless modes appear in the real-space entanglement spectrum, which is consistent with topological superconductivity.

Electrodynamics of superconductors: from Lorentz to Galilei at zero temperature. (arXiv:2401.04493v1 [cond-mat.supr-con])
Luca Salasnich

We discuss the derivation of the electrodynamics of superconductors coupled to the electromagnetic field from a Lorentz-invariant bosonic model of Cooper pairs. Our results are obtained at zero temperature where, according to the third law of thermodynamics, the entropy of the system is zero. In the nonrelativistic limit we obtain a Galilei-invariant superconducting system which differs with respect to the familiar Schr\"odinger-like one. From this point of view, there are similarities with the Pauli equation of fermions which is derived from the Dirac equation in the nonrelativistic limit and has a spin-magnetic field term in contrast with the Schr\"odinger equation. One of the peculiar effects of our model is the decay of a static electric field inside a superconductor exactly with the London penetration length. In addition, our theory predicts a modified D'Alembert equation for the massive electromagnetic field also in the case of nonrelativistic superconducting matter. We emphasize the role of the Nambu-Goldstone phase field which is crucial to obtain the collective modes of the superconducting matter field. In the special case of a nonrelativistic neutral superfluid we find a gapless Bogoliubov-like spectrum, while for the charged superfluid we obtain a dispersion relation that is gapped by the plasma frequency.

Observation of Higher Order Nodal Line Semimetal in Phononic Crystals. (arXiv:2401.04502v1 [cond-mat.mes-hall])
Qiyun Ma, Zhenhang Pu, Liping Ye, Jiuyang Lu, Xueqin Huang, Manzhu Ke, Hailong He, Weiyin Deng, Zhengyou Liu

Higher-order topological insulators and semimetals, which generalize the conventional bulk-boundary correspondence, have attracted extensive research interest. Among them, higher-order Weyl semimetals feature two-fold linear crossing points in three-dimensional (3D) momentum space, 2D Fermi-arc surface states, and 1D hinge states. Higher-order nodal-point semimetals possessing Weyl points or Dirac points have been implemented. However, higher-order nodal-line or nodal-surface semimetals remain to be further explored in experiments in spite of many previous theoretical efforts. In this work, we realize a second-order nodal-line semimetal in 3D phononic crystals. The bulk nodal lines, 2D drumhead surface states guaranteed by Zak phases, and 1D flat hinge states attributed to kz-dependent quadrupole moments, are observed in simulations and experiments. Our findings of nondispersive surface and hinge states may promote applications in acoustic sensing and energy harvesting.

Gate-tunable crossover between vortex-interaction and pinning dominated regimes in Josephson-coupled Lead-islands on graphene. (arXiv:2401.04532v1 [cond-mat.supr-con])
Suraina Gupta, Santu Prasad Jana, Rukshana Pervin, Anjan K. Gupta

Resistance of a Josephson junction array consisting of randomly distributed lead (Pb) islands on exfoliated single layer graphene shows a broad superconducting transition to zero with an onset temperature close to the transition temperature of bulk Pb. The transition evolves with the back-gate voltage and exhibits two peaks in temperature derivative of resistance. The region above the lower temperature peak is found to be well described by Berezinskii-Kosterlitz-Thouless model of thermal unbinding of vortex anti-vortex pairs while that below this peak fits well with the Ambegaokar- Halperin model of thermally-activated phase slip or vortex motion in Josephson junction arrays. Thus a gate-tunable crossover between interaction and pinning dominated vortices is inferred as the Josephson energy, dictating the pinning potential magnitude, increases with cooling while the effective screening length, dictating the range of inter-vortex interaction, reduces.

Topological transverse spin transport in a canted antiferromagnet/heavy metal heterostructure. (arXiv:2401.04582v1 [cond-mat.mes-hall])
Wesley Roberts, Bowen Ma, Martin Rodriguez-Vega, Gregory A. Fiete

We theoretically study the conditions under which a spin Nernst effect - a transverse spin current induced by an applied temperature gradient - can occur in a canted antiferromagnetic insulator, such as ${\rm LaFeO_3}$ and other materials of the same family. The spin Nernst effect may provide a microscopic mechanism for an experimentally observed anomalous thermovoltage in ${\rm LaFeO_3}$/Pt heterostructures, where spin is transferred across the insulator/metal interface when a temperature gradient is applied to ${\rm LaFeO_3}$ parallel to the interface [W. Lin ${\it et \; al}$, Nat. Phys. ${\bf 18}$, 800 (2022)]. We find that ${\rm LaFeO_3}$ exhibits a topological spin Nernst effect when inversion symmetry is broken on the axes parallel to both the applied temperature gradient and the direction of spin transport, which can result in a spin injection across the insulator/metal interface. Our work provides a general derivation of a symmetry-breaking-induced spin Nernst effect, which may open a path to engineering a finite spin Nernst effect in systems where it would otherwise not arise.

Revealing dark exciton signatures in polariton spectra of 2D materials. (arXiv:2401.04588v1 [cond-mat.mes-hall])
Beatriz Ferreira, Hangyong Shan, Roberto Rosati, Jamie M. Fitzgerald, Lukas Lackner, Bo Han, Martin Esmann, Patrick Hays, Gilbert Liebling, Kenji Watanabe, Takashi Taniguchi, Falk Eilenberger, Sefaattin Tongay, Christian Schneider, Ermin Malic

Dark excitons in transition metal dichalcogenides (TMD) have been so far neglected in the context of polariton physics due to their lack of oscillator strength. However, in tungsten-based TMDs, dark excitons are known to be the energetically lowest states and could thus provide important scattering partners for polaritons. In this joint theory-experiment work, we investigate the impact of the full exciton energy landscape on polariton absorption and reflectance. By changing the cavity detuning, we vary the polariton energy relative to the unaffected dark excitons in such a way that we open or close specific phonon-driven scattering channels. We demonstrate both in theory and experiment that this controlled switching of scattering channels manifests in characteristic sharp changes in optical spectra of polaritons. These spectral features can be exploited to extract the position of dark excitons. Our work suggests new possibilities for exploiting polaritons for fingerprinting nanomaterials via their unique exciton landscape.

Variational Monte-Carlo Approach for Hubbard Model Applied to Twisted Bilayer WSe$_2$ at Half-Filling. (arXiv:2401.04593v1 [cond-mat.str-el])
Andrzej Biborski, Paweł Wójcik, Michał Zegrodnik

We consider an effective Hubbard model with spin- and direction-dependent complex hoppings $t$, applied to twisted homobilayer WSe$_2$ using a variational Monte Carlo approach. The electronic correlations are taken into account by applying the Gutzwiller on-site correlator as well as long-range Jastrow correlators subjected to noninteracting part being of Pfaffian form. Our analysis shows the emergence of Mott insulating state at critical value of Hubbard interaction $U_{c1}\approx 6.5|t|\div7|t|$ estimated by extrapolating the density-density equal-time two-particle Green's functions. The signatures of an intermediate insulating phase between $U_{c1}$ and $U_{c2}\approx9.5|t|\div10|t|$ are also discussed. Furthermore, we report the formation of the $120^{\circ}$ in-plane N\'eel state indicated by the detailed analysis of the spin-spin correlation functions. As shown, switching between antiferromagnetic phases characterized by opposite chirality could be experimentally realized by the change of perpendicular electric field. In proper range of electric fields also a transition to in-plane ferromagnetic state appears.

Electric field manipulation of the Dzyaloshinskii-Moriya interacion in hybrid multiferroic structures. (arXiv:2401.04615v1 [cond-mat.mtrl-sci])
O.G. Udalov, R.V. Gorev, N.S. Gusev, A.V. Sadovnikov, M.V. Sapozhnikov

Hybrid multiferroic films are fabricated by depositing of Pt/Co/Pt multilayers onto [001] and [110] cuts of PMN-PT crystal. The dependence of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) on applied electric field is experimentally investigated in the system by the Brilloin light scattering method. A strong variation (from -0.2 to 0.8 mJ/m2) of the iDMI constant is observed when the electric field is applied. In the case of [001] cut, the observed changes in the iDMI have an isotropic character, while in the case of [110] cut they are anisotropic, which corresponds to the symmetry of the PMN-PT deformations. The change in the iDMI is accompanied by the formation of various unusual domain structures and skyrmion lattices. External control of the DMI with an electric field opens the way to manipulate topological magnetic solitons (such as skyrmions), which are promising objects for information processing and storage.

Weak antilocalization and localization in Eu$_2$Ir$_2$O$_7$ (111) thin films by reactive solid phase epitaxy. (arXiv:2401.04644v1 [cond-mat.str-el])
Xiaofeng Wu, Zhen Wang, Zhaoqing Ding, Zeguo Lin, Mingyu Yang, Minghui Gu, Meng Meng, Fang Yang, Xiaoran Liu, Jiandong Guo

Thin films of the pyrochlore iridates along the [111] direction have drawn significant attention to investigate exotic correlated topological phenomena. Here, we report the fabrication of Eu$_2$Ir$_2$O$_7$ thin films via reactive solid phase epitaxy using the pulsed laser deposition technique. We mainly focus on the transport properties of the films below the magnetic phase transition at 105 K. Analyses on the temperature and the field dependences of resistivity unveil the presence of weak antilocalization, a characteristic signature of the Weyl semimetallic state that has been "buried" by magnetism. Moreover, it is noteworthy that the contribution from many-body interactions in Eu2Ir2O7 thin films is enhanced at lower temperatures and competes with the weak antilocalization effect, and eventually drives the crossover to weak localization at 2 K.

Protected Weyl semimetals within 2D chiral classes. (arXiv:2401.04656v1 [cond-mat.mes-hall])
Faruk Abdulla

Weyl semimetals in three dimensions can exist independently of any symmetry apart from translations. Conversely, in two dimensions, Weyl semimetals are believed to require additional symmetries including crystalline symmetries to exist. In this study, we demonstrate that a 2D Weyl semimetal phase can exist in systems with Hamiltonians possessing internal symmetries, such as time reversal ${\cal T}$, charge conjugation ${\cal C}$ , and their combined chiral symmetry ${\cal S} = {\cal CT}$, only. Starting from a minimal-dimension Dirac Hamiltonian, we establish the presence of a stable Weyl semimetal phase in each of the five chiral classes: AIII, BDI, CII, DIII, and CI in two dimension. Similar to 3D Weyl semimetals where Weyl points possess nontrivial topological charges (Chern number), the Weyl points in WSMs within the 2D chiral classes are characterized by the $Z$ winding numbers. In accordance with the bulk-boundary correspondence, protected Fermi arc edge states emerge, connecting the projections of Weyl points that carry opposite topological charges. Unlike the surface states in 3D WSMs, the edge states of WSMs within 2D chiral classes are completely dispersionless and are always at the zero energy due to the protecting chiral symmetry.

Multiferroic quantum criticality in (Eu,Ba,Sr)TiO$_3$ solid solution. (arXiv:2401.04677v1 [cond-mat.mtrl-sci])
Dalibor Repček, Petr Proschek, Maxim Savinov, Martin Kachlík, Jiří Pospíšil, Jan Drahokoupil, Petr Doležal, Jan Prokleška, Stanislav Kamba

Based on the earlier published theory (Nature Mat. 18, 223-228 (2019)), a comprehensive experimental investigation of multiferroic quantum critical behavior of (Eu,Ba,Sr)TiO$_3$ polycrystalline and single crystal samples was performed. Presence of the displacive ferroelectric quantum criticality is revealed through non-classical ($T^2$) temperature scaling of inverse dielectric susceptibility up to 60 K. With increasing hydrostatic pressure, this ferroelectric quantum criticality is gradually suppressed. Inverse magnetic susceptibility follows classical Curie-Weiss law down to 4 K, but quantum fluctuations belonging to an antiferromagnetic phase transition ($T_{\mathrm{N}}$ < 0.8 K) change its scaling below 4 K to $T^{1.7}$ and $T^{2.0}$ for samples containing 29 % and 25 % of Eu$^{2+}$ ions, respectively. Observation of the coexisting ferroelectric and antiferromagnetic, i.e. multiferroic, quantum fluctuations and qualitative explanation why they are seen only in the immediate proximity of $T_{\mathrm{N}}$ is given.

Emergence of Larkin-Ovchinnikov-type superconducting state in a voltage-driven superconductor. (arXiv:2401.04684v1 [cond-mat.supr-con])
Taira Kawamura, Yoji Ohashi, H.T.C. Stoof

We theoretically investigate a voltage-biased normal metal-superconductor-normal metal (N-S-N) junction. Using the nonequilibrium Green's function technique, we derive a quantum kinetic equation, to determine the superconducting order parameter self-consistently. The derived equation is an integral-differential equation with memory effects. We solve this equation by converting it into a system of ordinary differential equations with the use of a pole expansion of the Fermi-Dirac function. When the applied voltage exceeds the critical value, the superconductor switches to the normal state. We find that when the voltage is decreased from the normal phase, the system relaxes to a Larkin-Ovchinnikov (LO)-type inhomogeneous superconducting state, even in the absence of a magnetic Zeeman field. We point out that the emergence of the LO-type state can be attributed to the nonequilibrium energy distribution of electrons due to the bias voltage. We also point out that the system exhibits bistability, which leads to hysteresis in the voltage-current characteristic of the N-S-N junction.

Atomic Layer Molecular Beam Epitaxy of Kagome Magnet RMn$_6$Sn$_6$ (R = Er, Tb) Thin Films. (arXiv:2401.04713v1 [cond-mat.mtrl-sci])
Shuyu Cheng, Igor Lyalin, Wenyi Zhou, Roland K. Kawakami

Kagome lattices have garnered substantial interest because their band structure consists of topological flat bands and Dirac cones. The RMn$_6$Sn$_6$ (R = rare earth) compounds are particularly interesting because of the existence of large intrinsic anomalous Hall effect (AHE) which originates from the gapped Dirac cones near the Fermi level. This makes RMn$_6$Sn$_6$ an outstanding candidate for realizing the high-temperature quantum anomalous Hall effect. The growth of RMn$_6$Sn$_6$ thin films is beneficial for both fundamental research and potential applications. However, most of the studies on RMn$_6$Sn$_6$ have focused on bulk crystals so far, and the synthesis of RMn$_6$Sn$_6$ thin films has not been reported so far. Here we report the atomic layer molecular beam epitaxy growth, structural and magnetic characterizations, and transport properties of ErMn$_6$Sn$_6$ and TbMn$_6$Sn$_6$ thin films. It is especially noteworthy that TbMn$_6$Sn$_6$ thin films have out-of-plane magnetic anisotropy, which is important for realizing the quantum anomalous Hall effect. Our work paves the avenue toward the control of the AHE using devices patterned from RMn$_6$Sn$_6$ thin films.

An Effective Theory for Graphene Nanoribbons with Junctions. (arXiv:2401.04715v1 [cond-mat.mes-hall])
Johann Ostmeyer, Lado Razmadze, Evan Berkowitz, Thomas Luu, Ulf-G. Meißner

Graphene nanoribbons are a promising candidate for fault-tolerant quantum electronics. In this scenario, qubits are realised by localised states that can emerge on junctions in hybrid ribbons formed by two armchair nanoribbons of different widths. We derive an effective theory based on a tight-binding ansatz for the description of hybrid nanoribbons and use it to make accurate predictions of the energy gap and nature of the localisation in various hybrid nanoribbon geometries. We discover, in addition to the well known localisations on junctions, which we call `Fuji', a new type of `Kilimanjaro' localisation smeared out over a segment of the hybrid ribbon. We show that Fuji localisations in hybrids of width $N$ and $N+2$ armchair nanoribbons occur around symmetric junctions if and only if $N\pmod3=1$, while edge-aligned junctions never support strong localisation. This behaviour cannot be explained relying purely on the topological $Z_2$ invariant, which has been believed the origin of the localisations to date.

Quantum Velocity Limits for Multiple Observables: Conservation Laws, Correlations, and Macroscopic Systems. (arXiv:2305.03190v4 [cond-mat.stat-mech] UPDATED)
Ryusuke Hamazaki

How multiple observables mutually influence their dynamics has been a crucial issue in statistical mechanics. We introduce a new concept, "quantum velocity limits," to establish a quantitative and rigorous theory for non-equilibrium quantum dynamics for multiple observables. Quantum velocity limits are universal inequalities for a vector the describes velocities of multiple observables. They elucidate that the speed of an observable of our interest can be tighter bounded when we have knowledge of other observables, such as experimentally accessible ones or conserved quantities, compared with the conventional speed limits for a single observable. We first derive an information-theoretical velocity limit in terms of the generalized correlation matrix of the observables and the quantum Fisher information. The velocity limit has various novel consequences: (i) conservation law in the system, a fundamental ingredient of quantum dynamics, can improve the velocity limits through the correlation between the observables and conserved quantities; (ii) speed of an observable can be bounded by a nontrivial lower bound from the information on another observable; (iii) there exists a notable non-equilibrium tradeoff relation, stating that speeds of uncorrelated observables, e.g., anti-commuting observables, cannot be simultaneously large; (iv) velocity limits for any observables on a local subsystem in locally interacting many-body systems remain convergent even in the thermodynamic limit. Moreover, we discover another distinct velocity limit for multiple observables on the basis of the local conservation law of probability current, which becomes advantageous for macroscopic transitions of multiple quantities.

A new microscopic representation of the spin dynamics in quantum systems with the Coulomb exchange interactions. (arXiv:2305.03826v2 [cond-mat.mtrl-sci] UPDATED)
Mariya Iv. Trukhanova, Pavel Andreev

There is a version of the Landau-Lifshitz equation that takes into account the Coulomb exchange interactions between atoms, expressed by the term $\sim\bm{s}\times\triangle\bm{s}$. On the other hand, magnetic atoms and ions have several valence electrons on the d-shell, and therefore the Hamiltonian of many-electron atoms with spins S>1 should include a biquadratic exchange interaction in the equation of magnetization (spin density) evolution. We first propose a new fundamental microscopic derivation of such an equation with an explicit form of biquadratic exchange interactions using the method of many-particle quantum hydrodynamics. Although we are considering a crystal lattice in which ions do not move, the resulting equations turn out to be hydrodynamic. The equations for the evolution of the spin density are obtained from the many-particle Schrodinger-Pauli equation and contain the contributions of the usual Coulomb exchange interactions and, first, the biquadratic exchange. Furthermore, the derived biquadratic exchamge torque in the spin density evolution equation contains the nematic tensor for the medium of atoms with spin $\textit{S=1}$. Our method may be very attractive for further studies of the magnetoelectric effect in multiferroics with exchange interactions.

Kondo screening and coherence in kagome local-moment metals: Energy scales of heavy fermions in the presence of flat bands. (arXiv:2305.16198v2 [cond-mat.str-el] UPDATED)
Christos Kourris, Matthias Vojta

The formation of a heavy Fermi liquid in metals with local moments is characterized by multiple energy and temperature scales, most prominently the Kondo temperature and the coherence temperature, characterizing the onset of Kondo screening and the emergence of Fermi-liquid coherence, respectively. In the standard setting of a wide conduction band, both scales depend exponentially on the Kondo coupling. Here we discuss how the presence of flat, i.e., dispersionless, conduction bands modifies this situation. Focussing on the case of the kagome Kondo-lattice model, we utilize a parton mean-field approach to determine the Kondo temperature and the coherence temperature as function of the conduction-band filling $n_c$, both numerically and analytically. For $n_c$ values corresponding to the flat conduction band located at the Fermi level, we show that the exponential is replaced by a linear dependence for the Kondo temperature and a quadratic dependence for the coherence temperature, while a cubic law emerges for the coherence temperature at $n_c$ corresponding to the band edge between the flat and dispersive bands. We discuss implications of our results for pertinent experimental data.

Exploring interacting chiral spin chains in terms of black hole physics. (arXiv:2305.19169v2 [cond-mat.str-el] UPDATED)
Ewan Forbes, Matthew D. Horner, Andrew Hallam, Joseph Barker, Jiannis K. Pachos

In this paper we explore the properties of a 1-dimensional spin chain in the presence of chiral interactions, focusing on the system's transition to distinct chiral phases for various values of the chiral coupling. By employing the mean field theory approximation we establish a connection between this chiral system and a Dirac particle in the curved spacetime of a black hole. Surprisingly, the black hole horizon coincides with the interface between distinct chiral phases. We examine the chiral properties of the system for homogeneous couplings and in scenarios involving position dependent couplings that correspond to black hole geometries. To determine the significance of interactions in the chiral chain we employ bosonization techniques and derive the corresponding Luttinger liquid model. Furthermore, we investigate the classical version of the model to understand the impact of the chiral operator on the spins and gain insight into the observed chirality. Our findings shed light on the behavior of the spin chain under the influence of the chiral operator, elucidating the implications of chirality in various contexts, including black hole physics.

Phase Diagram and Crossover Phases of Topologically Ordered Graphene Zigzag Nanoribbons: Role of Localization Effects. (arXiv:2307.04352v2 [cond-mat.str-el] UPDATED)
Hoang Anh Le, In Hwan Lee, Young Heon Kim, S.-R. Eric Yang

We computed the phase diagram of the zigzag graphene nanoribbons as a function of on-site repulsion, doping, and disorder strength. The topologically ordered phase undergoes topological phase transitions into crossover phases, which are new disordered phases with a nonuniversal topological entanglement entropy with significant variance. The topological order is destroyed by competition between localization effects and on-site repulsion. We found that strong on-site repulsion and/or doping weakens the nonlocal correlations between the opposite zigzag edges. In one of the crossover phases, both $\frac{e^-}{2}$ fractional charges and spin-charge separation were absent; however, charge-transfer correlations between the zigzag edges were possible. Another crossover phase contains $\frac{e^-}{2}$ fractional charges, but no charge transfer correlations. In low-doped zigzag ribbons the interplay between electron localization and on-site repulsion contributes to the spatial separation of quasi-degenerate gap-edge states and protects the charge fractionalization against quantum fluctuations. In all these effects, mixed chiral gap-edge states play an important role. The properties of nontopological strongly disordered and strongly repulsive phases are also observed. Each phase of the phase diagram has a different zigzag-edge structure.

Generation of phonon quantum states and quantum correlations among single photon emitters in hexagonal boron nitride. (arXiv:2308.06244v2 [quant-ph] UPDATED)
Hugo Molinares, Fernanda Pinilla, Enrique Muñoz, Francisco Muñoz, Vitalie Eremeev

Hexagonal boron nitride exhibits two types of defects with great potential for quantum information technologies: single-photon emitters (SPEs) and one-dimensional grain boundaries hosting topologically-protected phonons, termed as {\it{topologically-protected phonon lines}} (TPL). Here, by means of a simple effective model and density functional theory calculations, we show that it is possible to use these phonons for the transmission of information. Particularly, a single SPE can be used to induce single-, two- and qubit-phonon states in the one dimensional channel, and \textit{(ii)} two distant SPEs can be coupled by the TPL that acts as a waveguide, thus exhibiting strong quantum correlations. We highlight the possibilities offered by this material-built-in nano-architecture as a phononic device for quantum information technologies.

Disorder and diffuse scattering in single-chirality (TaSe$_4$)$_2$I crystals. (arXiv:2309.10236v3 [cond-mat.str-el] UPDATED)
Jacob A. Christensen, Simon Bettler, Kejian Qu, Jeffrey Huang, Soyeun Kim, Yinchuan Lu, Chengxi Zhao, Jin Chen, Matthew J. Krogstad, Toby J. Woods, Fahad Mahmood, Pinshane Y. Huang, Peter Abbamonte, Daniel P. Shoemaker

The quasi-one-dimensional chiral compound (TaSe$_4$)$_2$I has been extensively studied as a prime example of a topological Weyl semimetal. Upon crossing its phase transition temperature $T_\textrm{CDW}$ $\approx$ 263 K, (TaSe$_4$)$_2$I exhibits incommensurate charge density wave (CDW) modulations described by the well-defined propagation vector $\sim$(0.05, 0.05, 0.11), oblique to the TaSe$_4$ chains. Although optical and transport properties greatly depend on chirality, there is no systematic report about chiral domain size for (TaSe$_4$)$_2$I. In this study, our single-crystal scattering refinements reveal a bulk iodine deficiency, and Flack parameter measurements on multiple crystals demonstrate that separate (TaSe$_4$)$_2$I crystals have uniform handedness, supported by direct imaging and helicity dependent THz emission spectroscopy. Our single-crystal X-ray scattering and calculated diffraction patterns identify multiple diffuse features and create a real-space picture of the temperature-dependent (TaSe$_4$)$_2$I crystal structure. The short-range diffuse features are present at room temperature and decrease in intensity as the CDW modulation develops. These transverse displacements, along with electron pinning from the iodine deficiency, help explain why (TaSe$_4$)$_2$I behaves as an electronic semiconductor at temperatures above and below $T_\textrm{CDW}$, despite a metallic band structure calculated from density functional theory of the ideal structure.

Effect of interatomic repulsion on Majorana zero modes in a coupled quantum-dot-superconducting-nanowire hybrid system. (arXiv:2309.10888v2 [cond-mat.mes-hall] UPDATED)
R. Kenyi Takagui Perez, A. A. Aligia

We study the low-energy eigenstates of a topological superconductor wire modeled by a Kitaev chain, which is connected at one of its ends to a quantum dot through nearest-neighbor (NN) hopping and NN Coulomb repulsion. Using an unrestricted Hartree-Fock approximation to decouple the Coulomb term, we obtain that the quality of the Majorana end states is seriously affected by this term only when the dependence of the low-lying energies with the energy of the quantum dot shows a "diamond" shape, characteristic of short wires. We discuss limitations of the simplest effective models to describe the physics. We expect the same behavior in more realistic models for topological superconducting wires.

Phase chimera states on non-local hyperrings. (arXiv:2310.15540v2 [nlin.PS] UPDATED)
Riccardo Muolo, Thierry Njougouo, Lucia Valentina Gambuzza, Timoteo Carletti, Mattia Frasca

Chimera states are dynamical states where regions of synchronous trajectories coexist with incoherent ones. A significant amount of research has been devoted to study chimera states in systems of identical oscillators, non-locally coupled through pairwise interactions. Nevertheless, there is an increasing evidence, also supported by available data, that complex systems are composed by multiple units experiencing many-body interactions, that can be modeled by using higher-order structures beyond the paradigm of classic pairwise networks. In this work we investigate whether phase chimera states appear in this framework, by focusing on a novel topology solely involving many-body, non-local and non-regular interactions, hereby named non-local d-hyperring, being (d+1) the order of the interactions. We present the theory by using the paradigmatic Stuart-Landau oscillators as node dynamics, and show that phase chimera states emerge in a variety of structures and with different coupling functions. For comparison, we show that, when higher-order interactions are "flattened" to pairwise ones, the chimera behavior is weaker and more elusive.

Topological phases of many-body non-Hermitian systems. (arXiv:2311.03043v2 [quant-ph] UPDATED)
Kui Cao, Su-Peng Kou

We show that many-body fermionic non-Hermitian systems require two distinct sets of topological invariants to describe the topology of energy bands and quantum states respectively, with the latter yet to be explored. We identify 10 symmetry classes -- determined by particle-hole, linearized time-reversal, and linearized chiral symmetries. Each class has topological invariant associated with each dimension, dictating the topology of quantum states. These findings pave the way for deeper understanding of the topological phases of many-body non-Hermitian systems.

Impact of correlations on topology in Kane-Mele model decorated with impurities. (arXiv:2311.07379v2 [cond-mat.str-el] UPDATED)
Jan Skolimowski, Wojciech Brzezicki, Carmine Autieri

We propose an effective model for the study of the interplay between correlation and topology by decorating the Kane-Mele model with a set of localized interacting orbitals hybridized to just one sublattice, breaking the inversion symmetry. We show that in the time-reversal symmetric case, the interplay between interactions and hybridization extends the stability of the topological phase and depending on the driving mechanism very different behaviors are observed after the topological phase transition (TPT). We discuss the fate of the TPT in presence of weak ferromagnetic order, by introducing a weak local magnetic field at the localized orbitals, which splits the two band inversion points. One of the platforms to apply this model to are ferrovalley compounds, which are characterized by two independent band inversion points. Understanding this family of materials is crucial for the development of the valleytronics. An alternative to spintronics, which uses valley polarization as opposed to spin degrees of freedom as the building block, promises great opportunities for the development of information storage.

Extended edge modes and disorder preservation of a symmetry-protected topological phase out-of-equilibrium. (arXiv:2311.09610v2 [cond-mat.str-el] UPDATED)
Thomas L. M. Lane, Miklós Horváth, Kristian Patrick

The time evolution of topological systems is an active area of interest due to their expected applications in fault-tolerant quantum computing. Here, we analyze the dynamics of a non-interacting spinless fermion chain in its topological phase, quenched out-of-equilibrium by a Hamiltonian belonging to the same symmetry class. Due to particle-hole symmetry, the bulk properties of the system remain intact throughout its evolution. However, the boundary properties may be drastically altered, with the initially localized Majorana edge modes extending across the chain. Up to a timescale $t^*$, identified by area-law behavior of the entanglement entropy, these extended edge modes are an example of exotic effects in topological systems out-of-equilibrium. Further, whilst local disorder can be utilized to preserve localization and increase $t^*$, we still identify non-trivial dynamics in the Majorana polarization and Loschmidt echo.

Precursors to Topological Phase Transition in Topological Ladders. (arXiv:2311.11673v2 [cond-mat.mes-hall] UPDATED)
Seungju Han, Mahn-Soo Choi

We study the coupling of two topologcal subsystems in distinct topological states, and show that it leads to a precursor behavior of the topological phase transition in the overall system. This behavior is solely determined by the symmetry classes of the subsystem Hamiltonians and coupling terms, and is marked by the persistent existence of subgap states within the bulk energy gap. By investigating the critical current of Josephson junctions involving topological superconductors, we also illustrate that such subgap states play crucial roles in physical properties of nanoscale devices or materials.

Chiral symmetry breaking and topological charge of graphene nanoribbons. (arXiv:2312.05487v2 [cond-mat.mes-hall] UPDATED)
Hyun Cheol Lee, S.-R. Eric Yang

We explore the edge properties of rectangular graphene nanoribbons featuring two zigzag edges and two armchair edges. Although the self-consistent Hartree-Fock fields break chiral symmetry, our work demonstrates that graphene nanoribbons maintain their status as short-range entangled symmetry-protected topological insulators. The relevant symmetry involves combined mirror and time-reversal operations. In undoped ribbons displaying edge ferromagnetism, the band gap edge states with a topological charge form on the zigzag edges. An analysis of the anomalous continuity equation elucidates that this topological charge is induced by the gap term. In low-doped zigzag ribbons, where the ground state exhibits edge spin density waves, this topological charge appears as a nearly zero-energy edge mode.

From Fractional Quantum Anomalous Hall Smectics to Polar Smectic Metals: Nontrivial Interplay Between Electronic Liquid Crystal Order and Topological Order in Correlated Topological Flat Bands. (arXiv:2401.00363v2 [cond-mat.str-el] UPDATED)
Hongyu Lu, Han-Qing Wu, Bin-Bin Chen, Kai Sun, Zi Yang Meng

Integer or fractional quantum Hall crystals, states postulating the coexistence of charge order with integer or fractional quantum Hall effect, have long been proposed in theoretical studies in Landau levels. Inspired by recent experiments on integer or fractional quantum anomalous Hall (IQAH/FQAH) states in MoTe2 and rhombohedral multilayer graphene, this work examines the archetypal correlated flat band model on a checkerboard lattice at filling {\nu} = 2/3. Interestingly, at this filling level, we find that this topological flatband does not stabilize conventional FQAH states. Instead, the unique interplay between smectic charge order and topological order gives rise to two intriguing quantum states. As the interaction strength increases, the system first transitions from a Fermi liquid into FQAH smectic (FQAHS) states, where FQAH topological order coexists cooperatively with smectic charge order. With a further increase in interaction strength, the system undergoes another quantum phase transition and evolves into a polar smectic metal. Contrary to conventional smectic order and FQAHS states, this gapless state spontaneously breaks the two-fold rotational symmetry, resulting in a nonzero electric dipole moment and ferroelectric order. In addition to identifying the ground states, large-scale numerical simulations are also used to study low-energy excitations and thermodynamic characteristics. We find that FQAHS states exhibit two distinct temperature scales: the onset of charge order and the onset of the fractional Hall plateau, respectively. Interestingly, the latter is dictated by charge-neutral low-energy excitations with finite momenta, known as magnetorotons. Our studies suggest that these nontrivial phenomena could, in principle, be accessed in future experiments with moir\'e systems.

Found 6 papers in prb
Date of feed: Wed, 10 Jan 2024 04:17:02 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)

Exotic quantum liquids in Bose-Hubbard models with spatially modulated symmetries
Pablo Sala, Yizhi You, Johannes Hauschild, and Olexei Motrunich
Author(s): Pablo Sala, Yizhi You, Johannes Hauschild, and Olexei Motrunich

This work investigates the zero-temperature physics of generalized Bose-Hubbard models, which conserve finite Fourier momenta of the particle number. Analytical and numerical calculations predict a novel quasi-long-range order phase, in addition to more conventional Mott insulators. The former is characterized by a two-species Luttinger liquid in the infrared, with microscopic expectation values dressed by oscillatory contributions. The authors also conjecture that this phase is destroyed by the unbinding of topological defects along the temporal direction even when they are confined along the transverse direction.

[Phys. Rev. B 109, 014406] Published Tue Jan 09, 2024

Correlated phases in spin-orbit-coupled rhombohedral trilayer graphene
Jin Ming Koh, Jason Alicea, and Étienne Lantagne-Hurtubise
Author(s): Jin Ming Koh, Jason Alicea, and Étienne Lantagne-Hurtubise

Recent experiments indicate that crystalline graphene multilayers exhibit much of the richness of their twisted counterparts, including cascades of symmetry-broken states and unconventional superconductivity. Interfacing Bernal bilayer graphene with a ${\mathrm{WSe}}_{2}$ monolayer was shown to dram…

[Phys. Rev. B 109, 035113] Published Tue Jan 09, 2024

Fate of high winding number topological phases in the disordered extended Su-Schrieffer-Heeger model
Emmanuele G. Cinnirella, Andrea Nava, Gabriele Campagnano, and Domenico Giuliano
Author(s): Emmanuele G. Cinnirella, Andrea Nava, Gabriele Campagnano, and Domenico Giuliano

We use the Lindblad equation approach to investigate topological phases hosting more than one localized state at each side of a disordered Su-Schrieffer-Heeger chain with properly tuned long-range hoppings. Inducing a nonequilibrium steady state across the chain, we probe the robustness of each phas…

[Phys. Rev. B 109, 035114] Published Tue Jan 09, 2024

Robust and reentrant superconductivity in magic-angle twisted trilayer graphene
Jie Cao, Fenghua Qi, Yuanyuan Xiang, and Guojun Jin
Author(s): Jie Cao, Fenghua Qi, Yuanyuan Xiang, and Guojun Jin

The recent discovery of superconductivity in magic-angle twisted trilayer graphene (MATTG) has sparked significant interest. Here we focus on MATTG, where the low energy flat bands and linearly dispersive Dirac bands coexist and can be decoupled by external fields. Using a continuum model, we examin…

[Phys. Rev. B 109, 035115] Published Tue Jan 09, 2024

Experimental nuclear quadrupole resonance and computational study of the structurally refined topological semimetal ${\mathrm{TaSb}}_{2}$
T. Fujii, O. Janson, H. Yasuoka, H. Rosner, Yu. Prots, U. Burkhardt, M. Schmidt, and M. Baenitz
Author(s): T. Fujii, O. Janson, H. Yasuoka, H. Rosner, Yu. Prots, U. Burkhardt, M. Schmidt, and M. Baenitz

The electric field gradient (EFG) and magnetic excitation of TaSb2 were studied using nuclear quadrupole resonance (NQR) in a single crystal. The EFG parameters determined by measuring all expected NQR lines were corroborated by density functional theory (DFT) calculations. Despite the good agreement between the measured and calculated Sommerfeld coefficients, the spin-lattice relaxation rate was not captured by the DFT band calculations. To overcome this discrepancy, the authors propose a site-dependent in-gap state with an average energy gap of ~7 meV for the Sb sites and ~22 meV for the Ta site, which are much smaller than the semimetallic gap.

[Phys. Rev. B 109, 035116] Published Tue Jan 09, 2024

Theory of cuprate pseudogap as antiferromagnetic order with charged domain walls
R. S. Markiewicz and A. Bansil
Author(s): R. S. Markiewicz and A. Bansil

While magnetic fields generally compete with superconductivity, a type II superconductor can persist to very high fields by confining the field within the topological defects, namely the vortices. We propose that a similar physics underlies the pseudogap phase in the cuprates, where the relevant top…

[Phys. Rev. B 109, 045116] Published Tue Jan 09, 2024

Found 1 papers in prl
Date of feed: Wed, 10 Jan 2024 04:17:00 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)

Comment on “Anomalous Reentrant $5/2$ Quantum Hall Phase at Moderate Landau-Level-Mixing Strength”
Steven H. Simon
Author(s): Steven H. Simon
[Phys. Rev. Lett. 132, 029601] Published Tue Jan 09, 2024