Found 48 papers in cond-mat
Date of feed: Tue, 03 Oct 2023 00:30:00 GMT

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Pb$_9$Cu(PO$_4$)$_6$O is a charge-transfer semiconductor. (arXiv:2310.00006v1 [cond-mat.mtrl-sci])
Lorenzo Celiberti, Lorenzo Varrassi, Cesare Franchini

By means of density functional theory and constrained random phase approximation we analyze the bandstructure of Pb$_9$Cu(PO$_4$)$_6$O (named LK-99). Our data show that the lead-phosphate apatite LK-99 in the proposed Cu-doped structure is a semiconductor with predominant charge-transfer nature, a result incompatible with a superconducting behaviour. In order to understand the interesting electronic and magnetic properties of this compound, it will be necessary to study the actual response to doping, the possibility of alternative structural and stoichiometric (dis)orders and to clarify the magnetic interactions as well as their impact on the electronic structure.

Giant nonlinear optical wave mixing in van der Waals compound MnPSe3. (arXiv:2310.00026v1 [physics.optics])
Li Yue, Chang Liu, Shanshan Han, Hao Hong, Yijun Wang, Qiaomei Liu, Jiajie Qi, Yuan Li, Dong Wu, Kaihui Liu, Enge Wang, Tao Dong, Nanlin Wang

Optical nonlinearities, one of the most fascinating properties of two-dimensional (2D) materials, are essential for exploring novel physics in 2D systems and developing next-generation nonlinear optical applications. While tremendous efforts have been made to discover and optimize second-order nonlinear optical responses in various 2D materials, higher odd-order nonlinear processes, which are in general much less efficient than second order ones, have been paid less attention despite their scientific and applicational significance. Here we report giant odd-order nonlinear optical wave mixing in a correlated van der Waals insulator MnPSe3 at room temperature. Illuminated by two near-infrared femtosecond lasers simultaneously, it generates a series of degenerate and non-degenerate four- and six-wave mixing outputs, with conversion efficiencies up to the order of $10^{-4}$ and $10^{-6}$ for the four- and six-wave mixing processes, respectively, far exceeding the efficiencies of several prototypical nonlinear optical materials (GaSe, LiNbO3). This work highlights the intriguing prospect of transition metal phosphorous trichalcogenides for future research of the nonlinear light matter interactions in 2D systems and for potential nonlinear photonic applications.

Phases of Wilson Lines: Conformality and Screening. (arXiv:2310.00045v1 [hep-th])
Ofer Aharony, Gabriel Cuomo, Zohar Komargodski, Márk Mezei, Avia Raviv-Moshe

We study the rich dynamics resulting from introducing static charged particles (Wilson lines) in 2+1 and 3+1 dimensional gauge theories. Depending on the charges of the external particles, there may be multiple defect fixed points with interesting renormalization group flows connecting them, or an exponentially large screening cloud can develop (defining a new emergent length scale), screening the bare charge entirely or partially. We investigate several examples where the dynamics can be solved in various weak coupling or double scaling limits. Sometimes even the elementary Wilson lines, corresponding to the lowest nontrivial charge, are screened. We consider Wilson lines in 3+1 dimensional gauge theories including massless scalar and fermionic QED$_4$, and also in the ${\mathcal N}=4$ supersymmetric Yang-Mills theory. We also consider Wilson lines in 2+1 dimensional conformal gauge theories such as QED$_3$ with bosons or fermions, Chern-Simons-Matter theories, and the effective theory of graphene. Our results in 2+1 dimensions have potential implications for graphene, second-order superconducting phase transitions, etc. Finally, we comment on magnetic line operators in 3+1 dimensions ('t Hooft lines) and argue that our results for the infrared dynamics of electric and magnetic lines are consistent with non-Abelian electric-magnetic duality.

Topological Localized Modes In Moir\'{e} Lattices of Bilayer Elastic Plates With Resonators. (arXiv:2310.00182v1 [cond-mat.mes-hall])
Tamanna Akter Jui, Raj Kumar Pal

We investigate the existence of higher order topological localized modes in moir\'{e} lattices of bilayer elastic plates. Each plate has a hexagonal array of discrete resonators and one of the plates is rotated an angle ($21.78^\circ$) which results in a periodic moir\'{e} lattice with the smallest area. The two plates are then coupled by inter-layer springs at discrete locations where the top and bottom plate resonators coincide. Dispersion analysis using the plane wave expansion method reveals that a bandgap opens on adding the inter-layer springs. The corresponding topological index, namely fractional corner mode, for bands below the bandgap predicts the presence of corner localized modes in a finite structure. Numerical simulations of frequency response show localization at all corners, consistent with the theoretical predictions. The considered continuous elastic bilayered moir\'{e} structures opens opportunities for novel wave phenomena, with potential applications in tunable energy localization and vibration isolation.

Photosynthetically-powered phototactic active nematic fluids and gels. (arXiv:2310.00203v1 [cond-mat.soft])
Andrii Repula, Colin Gates, Jeffrey C. Cameron, Ivan I. Smalyukh

One of the most ancient forms of life dating to ~3.5 billion years ago, cyanobacteria are highly abundant organisms that convert light into energy and motion, often within conjoined filaments and larger colonies. We study how gradients of light intensity trigger orderly phototactic motions and dense bacterial communities, which remained quantitatively unexplored despite being among the oldest forms of active living matter on Earth. The phototaxis drives a transition from initially polar motions of semiflexible long filaments along complex curved spatiotemporal trajectories confined within illuminated areas to their bipolar motility in the ensuing crowded environment. We demonstrate how simply shining light causes a spontaneous self-assembly of two- and three-dimensional active nematic states of cyanobacterial filaments, with a plethora of motile and static topological defects. We quantify light-controlled evolutions of orientational and velocity order parameters during the transition between disordered and orientationally ordered states of our photosynthetic active matter, as well as the subsequent active nematic's fluid-gel transformation. Patterned illumination and foreign inclusions with different shapes interact with cyanobacterial active nematics in nontrivial ways, while inducing soft interfacial boundary conditions and quasi-boojum-like defects. Commanding this cyanobacterial collective behavior could aid inhibiting generation of toxins or enhancing production of oxygen and biomaterials.

A molecular Ferroelectric thin film of imidazolium perchlorate on Silicon. (arXiv:2310.00439v1 [cond-mat.mtrl-sci])
Congqin Zheng, Xin Li, Yuhui Huang, Yongjun Wu, Zijian Hong

Molecular ferroelectric materials have attracted widespread attention due to their abundant chemical diversity, structural tunability, low synthesis temperature, and high flexibility. Meanwhile, the integration of molecular ferroelectric materials and Si is still challenging, while the fundamental understanding of the ferroelectric switching process is still lacking. Herein, we have successfully synthesized the imidazole perchlorate (ImClO4) single crystals and a series of high-quality highly-oriented thin films on a Si substrate. A high inverse piezoelectric coefficient (55.7 pm/V) is demonstrated for the thin films. Two types of domain bands can be observed (in the size of a few microns): type-I band tilts ~60{\deg} with respect to the horizontal axis, while the type-II band is perpendicular to the horizontal axis. Most of the domain walls (DWs) are 180{\deg} DWs for the two bands, while some 109{\deg} DWs can also be observed. Interestingly, the DWs in type-I band are curved, charged domain walls; while the 180{\deg} DWs in type-II band are straight, noncharged domain walls. After applying +20 V for 5 s through a PFM tip, the 180{\deg} DWs in type-I band shrink first, then disconnect from the band boundary, forming a needle-like domain with a size of ~100 nm. The needle-like domain will extend toward the band boundary after an inverse bias is applied (-20 V), and expand along the band boundary after touching the boundary. Whereas for the type-II domain band, the 180{\deg} DWs are more mobile than the 109{\deg} domain walls, which displaces ~500 nm after applying +20 V. While such displacement is much shorter after the application of a negative bias for the same duration, starting from the positively poled sample. We hope to spur further interest in the on-chip design of the molecular ferroelectrics based electronic devices.

Quantum Materials Group Annual Report 2022. (arXiv:2310.00456v1 [cond-mat.mes-hall])
P. Kumari, S. Rani, S. Kar, T. Mukherjee, S. Majumder, K. Kumari, S. J. Ray

The Quantum Materials group at Indian Institute of Technology Patna is working on a range of topics relating to nanoelectronics, spintronics, clean energy and memory design etc. The PI has past experiences of working extensively with superconducting systems like cuprates [1, 2], ruthanate [3], pnictide [4, 5], thin film heterostructures [6, 7] etc and magnetic recording media [8, 9] etc. In this report, we have summarised the ongoing works in our group. We explored a range of functional materials like two-dimensional materials, oxides. topological insulators, organic materials etc. using a combination of experimnetal and computational tools. Some of the useful highlights are as follows: (a) tuning and control of the magnetic and electronic state of 2D magentic materials with rapid enhancement in the Curie temperature, (b) Design and detection of single electron transistor based nanosensors for the detection of biological species with single molecular resolution, (c) Observation of non-volatile memory behaviour in the hybrid structures made of perovskite materials and 2D hybrids. The results offer useful insight in the design of nanoelectronic architecrures for diverse applications.

Microscopic Insights into London Penetration Depth: Application to CeCoIn$^{}_{5}$. (arXiv:2310.00499v1 [cond-mat.supr-con])
Mehdi Biderang, Jeehoon Kim, Reza Molavi, Alireza Akbari

We propose a comprehensive theoretical formulation of magnetic penetration depth, $\lambda(T)$, based on the microscopic calculations for a general superconducting gap symmetry. Our findings admit the significant role of band structure and Fermi surface topology together with the symmetry of superconducting order parameter. We employ our findings pertaining to the heavy-fermion superconductor CeCoIn$_5$ to explore both local and non-local behaviors in response to an external magnetic field across varying temperatures. Our calculations in the low-temperature regime offer compelling macroscopic evidence of the nodal character within the superconducting state with $d_{x^2-y^2}$ symmetry. Furthermore, our findings align with the characteristics of London-type superconductivity, holding significant implications for upcoming experiments.

Quantum spin Hall states in the lateral heteromonolayers of WTe2-MoTe2. (arXiv:2310.00515v1 [cond-mat.mtrl-sci])
Mari Ohfuchi, Akihiko Sekine

We used density functional theory to investigate the lateral heteromonolayers of WTe2 and MoTe2. We confirmed that topologically nontrivial and trivial phases are energetically favored for the WTe2 and MoTe2 monolayers, taken out of bulk Td-WTe2 and 2H-MoTe2, respectively. We considered heteromonolayers consisting of these stable building blocks. In the Td-WTe2 and 2H-MoTe2 heteromonolayers with the interfaces oriented perpendicular to the dimer chains of W atoms in Td-WTe2 (y direction), two pairs of helical (quantum spin Hall [QSH]) states, one at each interface, connect the valence and conduction bands. The strain induced by the large lattice mismatch of the two materials in the y direction widens the band gap of the QSH insulator of the Td-WTe2 monolayer and is essential for electronic applications. Furthermore, one-dimensional channels embedded in the layer can help avoid chemical degradation from the edges and facilitate the densification of conducting channels. For the heteromonolayer with interfaces in the x direction, the difference in atomic structure between the two interfaces due to low symmetry creates an energy difference between two helical states and a potential gradient in the wide band gap 2H-MoTe2 region, resulting in various interface localized bands.

{SSH coupled-spring systems. (arXiv:2310.00547v1 [cond-mat.other])
Jie-Ying Kuo, Tsung-Yen Lee, Yi-Chia Chiu, Sheng-Rong Liao, Hsien-chung Kao

It is known that there is also a topological phase in the SSH coupled-spring system with the fixed-end boundary conditions. When this is the case, there would exist edge modes on its boundaries. In contrast, if the system satisfies the free-end boundary conditions, there is no edge mode, even if it is the topological phase. We show that by varying the force constant of the spring by the boundary in such a system, edge modes would generally appear independent of whether the bulk of the system is in the topological or trivial phases. Moreover, edge modes could exist even if the system satisfies the free-end boundary conditions.

Allotropic transition of Dirac semimetal {\alpha}-Sn to superconductor {\beta}-Sn induced by irradiation of focused ion beam. (arXiv:2310.00652v1 [cond-mat.mtrl-sci])
Kohdai Inagaki, Keita Ishihara, Tomoki Hotta, Yuichi Seki, Takahito Takeda, Tatsuhiro Ishida, Daiki Ootsuki, Ikuto Kawasaki, Shin-ichi Fujimori, Masaaki Tanaka, Le Duc Anh, Masaki Kobayashi

Diamond-type structure allotrope {\alpha}-Sn is attracting much attention as a topological Dirac semimetal (TDS). In this study, we demonstrate that {\alpha}-Sn undergoes a phase transition to another allotrope {\beta}-Sn with superconductivity at low temperature by irradiating with a focused Ga ion beam (FIB). To clarify the transition mechanism, we performed X-ray photoemission spectroscopy (XPS) measurements on an {\alpha}-Sn thin film irradiated with FIB and an as-grown {\alpha}-Sn thin film. The XPS results suggest that the local annealing, which is one of the side effects of FIB, causes the transformation from {\alpha}-Sn into {\beta}-Sn. Furthermore, the difference in the chemical states between {\alpha}-Sn and {\beta}-Sn can be quantitatively explained by the crystal structures rather than the degree of metallicity reflecting the conductivity. These results propose a new way of fabricating TDS/superconductor in-plane heterostructures based on {\alpha}-Sn and {\beta}-Sn.

Classification of High-Ordered Topological Nodes Towards MFBs in Twisted Bilayers. (arXiv:2310.00662v1 [cond-mat.str-el])
Fan Cui, Congcong Le, Qiang Zhang, Xianxin Wu, Jiangping Hu, Ching-Kai Chiu

At magic twisted angles, Dirac cones in twisted bilayer graphene (TBG) can evolve into flat bands, serving a critical playground for the study of strongly correlated physics. When chiral symmetry is introduced, rigorous mathematical proof confirms that the flat bands are locked at zero energy in the entire Moir\'{e} Brillouin zone (BZ). Yet, TBG is not the sole platform that exhibits this absolute band flatness. Central to this flatness phenomenon are topological nodes and their specific locations in the BZ. In this study, considering TBSs that preserve chiral symmetry, we classify various ordered topological nodes in base layers and all possible node locations across different BZs. Specifically, we constrain the node locations to rotational centers, such as $\Gamma$ and $\text{M}$ points, to ensure the interlayer coupling retains equal strength in all directions. Using this classification as a foundation, we systematically identify the conditions under which MFBs emerge. Additionally, through the extension of holomorphic functions, we provide a proof that flat bands are locked at zero energy, shedding light on the origin of the band flatness. Remarkably, beyond Dirac cones, numerous twisted bilayer nodal platforms can host the flat bands with the degeneracy number more than two, such as four-fold, six-fold, and eight-fold. This multiplicity of degeneracy in flat bands might unveil more complex and enriched correlation physics.

Low-energy Landau levels in monolayer graphene with proximity-induced spin-orbit coupling. (arXiv:2310.00686v1 [cond-mat.mes-hall])
Qing Rao, Hongxia Xue, Dong-Keun Ki

In this study, we investigate the effect of proximity-induced spin-orbit coupling (SOC) on Landau levels in graphene-transition metal dichalcogenides heterostructures. Using a simple theoretical model, we show that the SOC splits the electronic band in graphene at zero magnetic field that causes Landau level crossings at finite magnetic fields in quantum Hall regime. In particular, we find that the crossings among a few low-energy Landau levels sensitively depend on the strength of the SOC, suggesting that it can be used to estimate the SOC strengths in the system. To demonstrate this, we present an experimental signature of such Landau level crosssings and discuss its implications by comparing the data with calculation results. Our study provides a practical strategy to analyze Landau level spectrum in graphene with SOC.

Electronic properties of kagome metal ScV6Sn6 using high field torque magnetometry. (arXiv:2310.00751v1 [cond-mat.str-el])
Keshav Shrestha, Binod Regmi, Ganesh Pokharel, Seong-Gon Kim, Stephen D. Wilson, David E. Graf, Birendra A. Magar, Cole Phillips, Thinh Nguyen

This work presents electronic properties of the kagome metal ScV6Sn6 using de Haas-van Alphen (dHvA) oscillations and density functional theory (DFT) calculations. The torque signal with the applied fields up to 43 T shows clear dHvA oscillations with six major frequencies, five of them are below 400 T (low frequencies) and one is nearly 2800 T (high frequency). The Berry phase calculated using the Landau level fan diagram near the quantum limit is approximately {\pi}, which suggests the non-trivial band topology in ScV6Sn6. To explain the experimental data, we computed the electronic band structure and Fermi surface using DFT in both the pristine and charge density wave (CDW) phases. Our results confirm that the CDW phase is energetically favorable, and the Fermi surface undergoes a severe reconstruction in the CDW state. Furthermore, the angular dependence of the dHvA frequencies are consistent with the DFT calculations. The detailed electronic properties presented here are invaluable for understanding the electronic structure and CDWorder in ScV6Sn6, as well as in other vanadium-based kagome systems.

High-temperature magneto-inter-chirality oscillations in 2D systems with strong spin-orbit coupling. (arXiv:2310.00774v1 [cond-mat.mes-hall])
M.E. Raikh

Conventional magneto-oscillations of conductivity in three dimensions are washed out as the temperature exceeds the spacing between the Landau levels. This is due to smearing of the Fermi distribution. In two dimensions, in the presence of two or more size-quantization sub-bands, there is an additional type of magneto-oscillations, usually referred to as magneto-inter-sub-band oscillations, which do not decay exponentially with temperature. The period of these oscillations is determined by the condition that the energy separation between the sub-bands contains an integer number of Landau levels. Under this condition, which does not contain the Fermi distribution, the inter-sub-band scattering rate is maximal. Here we show that, with only one sub-band, high-temperature oscillations are still possible. They develop when the electron spectrum is split due to the spin-orbit coupling. For these additional oscillations, the coupling enters both, the period and the decay rate.

Impact of transforming interface geometry on edge states in valley photonic crystals. (arXiv:2310.00858v1 [physics.optics])
Di Yu, Sonakshi Arora, L. Kuipers

Topologically protected edge states arise at the interface of two topologically distinct valley photonic crystals. In this work, we investigate how tailoring the interface geometry, specifically from a zigzag interface to a glide plane, profoundly affects these edge states. Near-field measurements demonstrate how this transformation significantly changes the dispersion relation of the edge mode. We observe a transition from gapless edge states to gapped ones, accompanied by the occurrence of slow light within the Brillouin zone, rather than at its edge. Additionally, we simulate the propagation of the modified edge states through a specially designed valley-conserving defect. The simulations show, by monitoring the transmittance of this defect, how the robustness to backscattering gradually decreases, suggesting a disruption of valley-dependent transport. These findings demonstrate how the gradual emergence of valley-dependent gapless edge states in a valley photonic crystal depends on the geometry of its interface.

Improving Hydrogen evolution catalytic activity of 2D carbon allotrope Biphenylene with B, N, P doping: Density Functional Theory Investigations. (arXiv:2310.00932v1 [cond-mat.mtrl-sci])
Mukesh Singh, Alok Shukla, Brahmananda Charkraborty

Using a first principles approach, we studied the hydrogen evolution reaction activity of newly synthesized biphenylene and B, N, P decorated biphenylene sheet. hydrogen evolution reaction activity of pristine biphenylene sheet is not encouraging, as it is similar to pristine graphene. The Gibbs free energy and overpotential of P(N) doped on biphenylene sheet are 0.022 (-0.092) eV and 22 (92) mV, respectively. The reported Gibbs free energy and overpotential of Pt are 0.9 eV and 90 mV. Hence doping of P(N) atom on top of biphenylene sheet improves hydrogen evolution reaction activity much better (near to) Pt metal. We analyzed the adsorption mechanism of dopants (B, N, P) and hydrogen with Bader charge analysis and density of states analysis. P and N-decoration on biphenylene sheet change its electronic structure so that one obtains improved hydrogen evolution reaction activity for P and N-doped biphenylene sheet. Furthermore, the stability of N, P decorated biphenylene at room temperature with ab initio molecular dynamics and formation energy near that of biphenylene indicate experimental feasibility. We have compared all our best hydrogen evolution reaction activity results in the reaction coordinate and volcano plots of pristine, B, N, and P-doped BPh sheets. They indicate that P-doped biphenylene is a metal-free, powerful catalyst for hydrogen evolution reaction activities.

Crystal nucleation in a vapor deposited Lennard-Jones mixture. (arXiv:2310.01021v1 [cond-mat.soft])
Fabio Leoni, Hajime Tanaka, John Russo

Understanding the pathways to crystallization during the deposition of a vapor phase on a cold solid substrate is of great interest in industry, e.g., for the realization of electronic devices made of crystallites-free glassy materials, as well as in the atmospheric science in relation to ice nucleation and growth in clouds. Here we numerically investigate the nucleation process during the deposition of a glassformer by using a Lennard-Jones mixture, and compare the properties of this nucleation process with both its quenched counterpart and the bulk system. We find that all three systems homogeneously nucleate crystals in a narrow range of temperatures. However, the deposited layer shows a peculiar formation of ordered domains, promoted by the faster relaxation dynamics toward the free surface even in an as-deposited state. In contrast, the formation of such domains in the other systems occurs only when the structures are fully relaxed by quenching. Furthermore, the nucleus initially grows in an isotropic symmetrical manner, but eventually shows sub-3D growth due to its preference to grow along the basal plane, irrespective of the layer production procedure.

Elemental Ferroelectric Topological Insulator in $\psi$-bismuthene. (arXiv:2310.01027v1 [cond-mat.mtrl-sci])
Yan Liang, Xuening Han, Thomas Frauenheim, Fulu Zheng, Pei Zhao

Ferroelectric quantum spin Hall insulator (FEQSHI) exhibits coexisting ferroelectricity and time-reversal symmetry protected edge states, holding fascinating prospects for inviting both scientific and application advances, especially in two dimensions. However, all of the previously demonstrated FEQSHIs consist two or more constituent elements. We herein propose the $\psi$-bismuthene, an uncharted allotrope of bilayer Bi (110), to be the first example of 2D elemental FEQSHI. It is demonstrated that $\psi$-bismuthene harbors measurable ferroelectric polarization and nontrivial band gap with moderate switching barrier, which are highly beneficial for the detection and observation of the ferroelectric topologically insulating states. In addition, all-angle auxetic behavior with giant negative Poisson's ratio and ferroelectric controllable persistent spin helix in $\psi$-bismuthene are also discussed. The emergent elemental FEQSHI represents a novel domain for both fundamental physics and technological innovation.

Crystallographic-dependent bilinear magnetoelectric resistance in a thin WTe$_2$ layer. (arXiv:2310.01058v1 [cond-mat.mes-hall])
Tian Liu, Arunesh Roy, Jan Hidding, Homayoun Jafari, Dennis K. de Wal, Jagoda Slawinska, Marcos H. D. Guimarães, Bart J. van Wees

The recently reported Bilinear Magnetoeletric Resistance (BMR) in novel materials with rich spin textures, such as bismuth selenide (Bi$_2$Se$_3$) and tungsten ditelluride (WTe$_2$), opens new possibilities for probing the spin textures via magneto-transport measurements. By its nature, the BMR effect is directly linked to the crystal symmetry of the materials and its spin texture. Therefore, understanding the crystallographic dependency of the effect is crucial. Here we report the observation of crystallographic-dependent BMR in thin WTe$_2$ layers and explore how it is linked to its spin textures. The linear response measured in first harmonic signals and the BMR measured in second harmonic signals are both studied under a wide range of magnitudes and directions of magnetic field, applied current and at different temperatures. We discover a three-fold symmetry contribution of the BMR when current is applied along the a-axis of the WTe$_2$ thin layer at 10 K, which is absent for when current is applied along the b-axis.

Anomalous Hall transport by optically injected isospin degree of freedom in Dirac semimetal thin film. (arXiv:2310.01093v1 [cond-mat.mes-hall])
Yuta Murotani, Natsuki Kanda, Tomohiro Fujimoto, Takuya Matsuda, Manik Goyal, Jun Yoshinobu, Yohei Kobayashi, Takashi Oka, Susanne Stemmer, Ryusuke Matsunaga

Chirality of massless fermions emergent in condensed matter is a key to understand their characteristic behavior as well as to exploit their functionality. However, chiral nature of massless fermions in Dirac semimetals has remained elusive, due to equivalent occupation of carriers with the opposite chirality in thermal equilibrium. Here, we show that the isospin degree of freedom, which labels the chirality of massless carriers from a crystallographic point of view, can be injected by circularly polarized light. Terahertz Faraday rotation spectroscopy successfully detects the anomalous Hall conductivity by a light-induced isospin polarization in a three-dimensional Dirac semimetal, Cd$_3$As$_2$. Spectral analysis of the Hall conductivity reveals a long scattering time and a long decay time, which are characteristic of the isospin. The long-lived, robust, and reversible character of the isospin promises potential application of Dirac semimetals in future information technology.

Predicting emergence of crystals from amorphous matter with deep learning. (arXiv:2310.01117v1 [cond-mat.mtrl-sci])
Muratahan Aykol, Amil Merchant, Simon Batzner, Jennifer N. Wei, Ekin Dogus Cubuk

Crystallization of the amorphous phases into metastable crystals plays a fundamental role in the formation of new matter, from geological to biological processes in nature to synthesis and development of new materials in the laboratory. Predicting the outcome of such phase transitions reliably would enable new research directions in these areas, but has remained beyond reach with molecular modeling or ab-initio methods. Here, we show that crystallization products of amorphous phases can be predicted in any inorganic chemistry by sampling the crystallization pathways of their local structural motifs at the atomistic level using universal deep learning potentials. We show that this approach identifies the crystal structures of polymorphs that initially nucleate from amorphous precursors with high accuracy across a diverse set of material systems, including polymorphic oxides, nitrides, carbides, fluorides, chlorides, chalcogenides, and metal alloys. Our results demonstrate that Ostwald's rule of stages can be exploited mechanistically at the molecular level to predictably access new metastable crystals from the amorphous phase in material synthesis.

Skyrmion stripes in twisted double bilayer graphene. (arXiv:2310.01185v1 [cond-mat.mes-hall])
Debasmita Giri, Dibya Kanti Mukherjee, H.A. Fertig, Arijit Kundu

Two dimensional moir\'e systems have recently emerged as a platform in which the interplay between topology and strong correlations of electrons play out in non-trivial ways. Among these systems, twisted double bilayer graphene (TDBG) is of particular interest as its topological properties may be tuned via both twist angle and applied perpendicular electric field. In this system, energy gaps are observed at half filling of particular bands, which can be associated with correlated spin polarized states. In this work, we investigate the fate of these states as the system is doped away from this filling. We demonstrate that, for a broad range of fractional fillings, the resulting ground state is partially valley polarized, and supports multiple broken symmetries, including a textured spin order indicative of skyrmions, with a novel $\textit{stripe}$ ordering that spontaneously breaks $C_3$ symmetry. Experimental signatures of this state are discussed.

Correlation-induced phase transitions and mobility edges in a non-Hermitian quasicrystal. (arXiv:2310.01275v1 [quant-ph])
Tian Qian, Longwen Zhou

Non-Hermitian quasicrystal constitutes a unique class of disordered open system with PT-symmetry breaking, localization and topological triple phase transitions. In this work, we uncover the effect of quantum correlation on phase transitions and entanglement dynamics in non-Hermitian quasicrystals. Focusing on two interacting bosons in a Bose-Hubbard lattice with quasiperiodically modulated gain and loss, we find that the onsite interaction between bosons could drag the PT and localization transition thresholds towards weaker disorder regions compared with the noninteracting case. Moreover, the interaction facilitates the expansion of the critical point of a triple phase transition in the noninteracting system into a critical phase with mobility edges, whose domain could be flexibly controlled by tuning the interaction strength. Systematic analyses of the spectrum, inverse participation ratio, topological winding number, wavepacket dynamics and entanglement entropy lead to consistent predictions about the correlation-driven phases and transitions in our system. Our findings pave the way for further studies of the interplay between disorder and interaction in non-Hermitian quantum matter.

Hybrid light-matter states in topological superconductors coupled to cavity photons. (arXiv:2310.01296v1 [cond-mat.mes-hall])
Olesia Dmytruk, Marco Schirò

We consider a one-dimensional topological superconductor hosting Majorana bound states at its ends coupled to a single mode cavity. In the strong light-matter coupling regime, electronic and photonic degrees of freedom hybridize resulting in the formation of polaritons. We find the polariton spectrum by calculating the cavity photon spectral function of the coupled electron-photon system. In the topological phase the lower in energy polariton modes are formed by the bulk-Majorana transitions coupled to cavity photons and are also sensitive to the Majorana parity. In the trivial phase the lower polariton modes emerge due to the coupling of the bulk-bulk transitions across the gap to photons. Our work demonstrates the formation of polaritons in topological superconductors coupled to photons that contain information on the features of the Majorana bound states.

Optical conductivity and damping of plasmons due to electron-electron interaction. (arXiv:2310.01337v1 [cond-mat.str-el])
Prachi Sharma, Alessandro Principi, Giovanni Vignale, Dmitrii L. Maslov

We re-visit the issue of plasmon damping due to electron-electron interaction. The plasmon linewidth can related to the imaginary part of the charge susceptibility or, equivalently, to the real part of the optical conductivity, $\mathrm{Re}\sigma(q,\omega)$. Approaching the problem first via a standard semi-classical Boltzmann equation, we show that $\mathrm{Re}\sigma(q,\omega)$ of two-dimensional (2D) electron gas scales as $q^2T^2/\omega^4$ for $\omega\ll T$, which agrees with the results of Refs. [1] and [2] but disagrees with that of Ref. [3], according to which $\mathrm{Re}\sigma(q,\omega) \propto q^2T^2/\omega^2$. To resolve this disagreement, we re-derive $\mathrm{Re}\sigma(q,\omega)$ using the original method of Ref. {mishchenko:2004} for an arbitrary ratio $\omega/T$ and show that, while the last term is, indeed, present, it is subleading to the $q^2T^2/\omega^4$ term. We give a physical interpretation of both leading and subleading contributions in terms of the shear and bulk viscosities of an electron liquid, respectively. We also calculate $\mathrm{Re}\sigma(q,\omega)$ for a three-dimensional (3D) electron gas and doped monolayer graphene. We find that, with all other parameters being equal, finite temperature has the strongest effect on the plasmon linewidth in graphene, where it scales as $T^4\ln T$ for $\omega\ll T$.

Local markers for crystalline topology. (arXiv:2310.01398v1 [physics.optics])
Alexander Cerjan, Terry A. Loring, Hermann Schulz-Baldes

Over the last few years, crystalline topology has been used in photonic crystals to realize edge- and corner-localized states that enhance light-matter interactions for potential device applications. However, the band-theoretic approaches currently used to classify bulk topological crystalline phases cannot predict the existence, localization, or spectral isolation of any resulting boundary-localized modes. While interfaces between materials in different crystalline phases must have topological states at some energy, these states need not appear within the band gap, and thus may not be useful for applications. Here, we derive a class of local markers for identifying material topology due to crystalline symmetries, as well as a corresponding measure of topological protection. As our real-space-based approach is inherently local, it immediately reveals the existence and robustness of topological boundary-localized states, yielding a predictive framework for designing topological crystalline heterostructures. Beyond enabling the optimization of device geometries, we anticipate that our framework will also provide a route forward to deriving local markers for other classes of topology that are reliant upon spatial symmetries.

Manipulating polariton condensates by Rashba-Dresselhaus coupling at room temperature. (arXiv:2108.02057v2 [cond-mat.quant-gas] UPDATED)
Yao Li, Xuekai Ma, Xiaokun Zhai, Meini Gao, Haitao Dai, Stefan Schumacher, Tingge Gao

The spin-orbit coupling plays an important role in the spin Hall effect and the topological insulators. In addition, the spin-orbit coupled Bose-Einstein condensates show remarkable quantum many-body phase transition. In this work we tune the exciton polariton condensate by virtue of the Rashba-Dresselhaus (RD) spin-orbit coupling in a liquid-crystal filled microcavity where perovskite CsPbBr3 microplates act as the gain material at room temperature. We realize an artificial gauge field on the CsPbBr3 exciton polariton condensate, which splits the condensates with opposite spins in both momentum and real spaces. Our work paves the way to manipulate the exciton polariton condensate with a synthetic gauge field based on the RD spin-orbit coupling at room temperature.

Electric-field control of magnetic anisotropies: applications to Kitaev spin liquids and topological spin textures. (arXiv:2110.06503v3 [cond-mat.str-el] UPDATED)
Shunsuke C. Furuya, Masahiro Sato

Magnetic anisotropies often originate from the spin-orbit coupling and determine magnetic ordering patterns. We develop a microscopic theory for DC electric-field controls of magnetic anisotropies in magnetic Mott insulators and discuss its applications to Kitaev materials and topological spin textures. Throughout this paper, we take a microscopic approach based on Hubbard-like lattice models, tight-binding models with on-site interactions. We derive a low-energy spin Hamiltonian from a fourth-order perturbation expansion of the Hubbard-like model. We show in the presence of a strong intra-atomic spin-orbit coupling that DC electric fields add non-Kitaev interactions such as a Dzyaloshinskii-Moriya interaction and an off-diagonal $\Gamma'$ interaction to the Kitaev-Heisenberg model and can induce a topological quantum phase transition between Majorana Chern insulating phases. We also investigate the inter-atomic Rashba spin-orbit coupling and its effects on topological spin textures. DC electric fields turn out to create and annihilate magnetic skyrmions, hedgehogs, and chiral solitons. We propose several methods of creating topological spin textures with external electromagnetic fields. Our theory clarifies that the strong but feasible electric field can control Kitaev spin liquids and topological spin textures.

Advanced Thermostats for Molecular Dynamics. (arXiv:2205.06608v3 [cond-mat.stat-mech] UPDATED)
Roumen Tsekov

Advanced thermostats for molecular dynamics are proposed on the base of the rigorous Langevin dynamics. Because the latter accounts for the subsystem-bath interactions in details, the bath anisotropy and nonuniformity are described via the relevant friction tensor. The developed model reflects properly the relativistic dynamics of the subsystem evolution as well as the nonlinear friction, which can occur for fast particles with large momenta at elevated temperature.

Quantum Monte Carlo Study of Semiconductor Artificial Graphene Nanostructures. (arXiv:2210.14696v3 [cond-mat.mes-hall] UPDATED)
Gökhan Öztarhan, E. Bulut Kul, Emre Okcu, A. D. Güçlü

Semiconductor artificial graphene nanostructures where Hubbard model parameter $U/t$ can be of the order of 100, provide a highly controllable platform to study strongly correlated quantum many-particle phases. We use accurate variational and diffusion Monte Carlo methods to demonstrate a transition from antiferromagnetic to metallic phases for experimentally accessible lattice constant $a=50$ nm in terms of lattice site radius $\rho$, for finite sized artificial honeycomb structures nanopatterned on GaAs quantum wells containing up to 114 electrons. By analysing spin-spin correlation functions for hexagonal flakes with armchair edges and triangular flakes with zigzag edges, we show that edge type, geometry and charge nonuniformity affect the steepness and the crossover $\rho$ value of the phase transition. For triangular structures, the metal-insulator transition is accompanied with a smoother edge polarization transition.

Topological information device operating at the Landauer limit. (arXiv:2212.14862v2 [cond-mat.mes-hall] UPDATED)
A. Mert Bozkurt, Alexander Brinkman, İnanç Adagideli

We propose and theoretically investigate a novel Maxwell's demon implementation based on the spin-momentum locking property of topological matter. We use nuclear spins as a memory resource which provides the advantage of scalability. We show that this topological information device can ideally operate at the Landauer limit; the heat dissipation required to erase one bit of information stored in the demon's memory approaches $k_B T\ln2$. Furthermore, we demonstrate that all available energy, $k_B T\ln2$ per one bit of information, can be extracted in the form of electrical work. Finally, we find that the current-voltage characteristics of topological information device satisfy the conditions of an ideal memristor.

PiNNwall: Heterogeneous Electrode Models from Integrating Machine Learning and Atomistic Simulation. (arXiv:2303.15307v4 [cond-mat.mtrl-sci] UPDATED)
Thomas Dufils, Lisanne Knijff, Yunqi Shao, Chao Zhang

Electrochemical energy storage always involves the capacitive process. The prevailing electrode model used in the molecular simulation of polarizable electrode-electrolyte systems is the Siepmann-Sprik model developed for perfect metal electrodes. This model has been recently extended to study the metallicity in the electrode by including the Thomas-Fermi screening length. Nevertheless, a further extension to heterogeneous electrode models requires introducing chemical specificity, which does not have any analytical recipes. Here, we address this challenge by integrating the atomistic machine learning code (PiNN) for generating the base charge and response kernel and the classical molecular dynamics code (MetalWalls) dedicated to the modeling of electrochemical systems, and this leads to the development of the PiNNwall interface. Apart from the cases of chemically doped graphene and graphene oxide electrodes as shown in this study, the PiNNwall interface also allows us to probe polarized oxide surfaces in which both the proton charge and the electronic charge can coexist. Therefore, this work opens the door for modeling heterogeneous and complex electrode materials often found in energy storage systems.

Real-time observation of magnetization and magnon dynamics in a two-dimensional topological antiferromagnet MnBi2Te4. (arXiv:2304.09390v2 [cond-mat.mes-hall] UPDATED)
F. Michael Bartram, Meng Li, Liangyang Liu, Zhiming Xu, Yongchao Wang, Mengqian Che, Hao Li, Yang Wu, Yong Xu, Jinsong Zhang, Shuo Yang, Luyi Yang

Atomically thin van der Waals magnetic materials have not only provided a fertile playground to explore basic physics in the two-dimensional (2D) limit but also created vast opportunities for novel ultrafast functional devices. Here we systematically investigate ultrafast magnetization dynamics and spin wave dynamics in few-layer topological antiferromagnetic MnBi2Te4 crystals as a function of layer number, temperature, and magnetic field. We find laser-induced (de)magnetization processes can be used to accurately track the distinct magnetic states in different magnetic field regimes, including showing clear odd-even layer number effects. In addition, strongly field-dependent antiferromagnetic magnon modes with tens of gigahertz frequencies are optically generated and directly observed in the time domain. Remarkably, we find that magnetization and magnon dynamics can be observed in not only the time-resolved magneto-optical Kerr effect but also the time resolved reflectivity, indicating strong correlation between the magnetic state and electronic structure. These measurements present the first comprehensive overview of ultrafast spin dynamics in this novel 2D antiferromagnet, paving the way for potential applications in 2D antiferromagnetic spintronics and magnonics as well as further studies of ultrafast control of both magnetization and topological quantum states.

Studies of two-dimensional material resistive random-access memory by kinetic Monte Carlo simulations. (arXiv:2304.11345v2 [cond-mat.mtrl-sci] UPDATED)
Ying-Chuan Chen, Yu-Ting Chao, Edward Chen, Chao-Hsin Wu, Yuh-Renn Wu

Resistive memory based on 2D WS2, MoS2, and h-BN materials has been studied, including experiments and simulations. The influences with different active layer thicknesses have been discussed, including experiments and simulations. The thickness with the best On/Off ratio is also found for the 2D RRAM. This work reveals fundamental differences between a 2D RRAM and a conventional oxide RRAM. Furthermore, from the physical parameters extracted with the KMC model, the 2D materials have a lower diffusion activation energy from the vertical direction, where a smaller bias voltage and a shorter switching time can be achieved. It was also found the diffusion activation energy from the CVD-grown sample is much lower than the mechanical exfoliated sample. The result shows MoS2 has the fastest switching speed among three 2D materials.

Correlated Insulator and Chern Insulators in Pentalayer Rhombohedral Stacked Graphene. (arXiv:2305.03151v2 [cond-mat.mes-hall] UPDATED)
Tonghang Han, Zhengguang Lu, Giovanni Scuri, Jiho Sung, Jue Wang, Tianyi Han, Kenji Watanabe, Takashi Taniguchi, Hongkun Park, Long Ju

Rhombohedral stacked multilayer graphene is an ideal platform to search for correlated electron phenomena, due to its pair of flat bands touching at zero energy and further tunability by an electric field. Furthermore, its valley-dependent Berry phase at zero energy points to possible topological states when the pseudospin symmetry is broken by electron correlation. However, experimental explorations of these opportunities are very limited so far, due to a lack of devices with optimized layer numbers and configurations. Here we present electron transport measurements of hBN-encapsulated pentalayer graphene at down to 100 milli-Kelvin. We observed a correlated insulating state with >MOhm resistance at zero charge density and zero displacement field, where the tight-binding calculation predicts a metallic ground state. By increasing the displacement field, we observed a Chern insulator state with C = -5 and two other states with C = -3 at a low magnetic field of ~1 Tesla. At high displacement fields and charge densities, we observed isospin-polarized quarter- and half-metals. Therefore, rhombohedral-stacked pentalayer graphene is the first graphene system to exhibit two different types of Fermi-surface instabilities: driven by a pair of flat bands touching at zero energy, and by the Stoner mechanism in a single flat band. Our results demonstrate a new direction to explore intertwined electron correlation and topology phenomena in natural graphitic materials without the need of moir\'e superlattice engineering.

MilliKelvin microwave impedance microscopy in a dry dilution refrigerator. (arXiv:2305.03757v2 [] UPDATED)
Leonard Weihao Cao, Chen Wu, Rajarshi Bhattacharyya, Ruolun Zhang, Monica T. Allen

Microwave impedance microscopy (MIM) is a near-field imaging technique that has been used to visualize the local conductivity of materials with nanoscale resolution across the GHz regime. In recent years, MIM has shown great promise for the investigation of topological states of matter, correlated electronic states and emergent phenomena in quantum materials. To explore these low-energy phenomena, many of which are only detectable in the milliKelvin regime, we have developed a novel low-temperature MIM incorporated into a dilution refrigerator. This setup which consists of a tuning-fork-based atomic force microscope with microwave reflectometry capabilities, is capable of reaching temperatures down to 70 mK during imaging and magnetic fields up to 9 T. To test the performance of this microscope, we demonstrate microwave imaging of the conductivity contrast between graphite and silicon dioxide at cryogenic temperatures and discuss the resolution and noise observed in these results. We extend this methodology to visualize edge conduction in Dirac semimetal cadmium arsenide in the quantum Hall regime

Coexistence of Dirac Fermions and Magnons in a Layered Two-Dimensional Semiquinoid Metal-Organic Framework. (arXiv:2305.03867v2 [cond-mat.str-el] UPDATED)
Christopher Lane, Yixuan Huang, Jian-Xin Zhu

We predict the magnetic and electronic properties of a novel metal-organic framework. By combining density functional theory and density matrix renormalization group approaches, we find the diatomic Kagome crystal structure of the metal-semiquinoid framework (H$_2$NMe$_2$)$_2$M$_2$(Cl$_2$dhbq)$_3$ (M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) to host a rich variety of antiferromagnetic (AFM) and ferromagnetic (FM) Dirac semimetallic, spin-polarized Dirac fermions, and flat band magnetic insulators and metallic phases. Concomitantly, the spin excitation spectrum of the various magnetic systems display multiple Dirac-like and nodal-ring crossings. This suggests that the metal-semiquinoid system is an ideal platform for examining the intertwining of Dirac fermions and magnons.

Zero mode-soliton duality and pKdV kinks in Boussinesq system for non-linear shallow water waves. (arXiv:2305.04037v2 [hep-th] UPDATED)
H. Blas, Ronal A. DeLaCruz-Araujo, N. I. Reynaldo Jr., N. Santos, S. Tech, H.E.P. Cardoso

A Boussinesq system for a non-linear shallow water is considered. The nonlinear and topological effects are examined through an associated matrix spectral problem. It is shown an equivalence relationship between the bound states and topological soliton charge densities which resembles a formula of the Atiyah-Patodi-Singer-type index theorem. The zero mode components describe a topologically protected Kelvin wave of KdV-type and a novel Boussinesq-type field. We show that either the $1+1$ dimensional pKdV kink or the Kelvin mode can be mapped to the bulk velocity potential in $2+1$ dimensions.

Full Counting Statistics of Yu-Shiba-Rusinov Bound States. (arXiv:2305.04758v2 [cond-mat.mes-hall] UPDATED)
David Christian Ohnmacht, Wolfgang Belzig, Juan Carlos Cuevas

With the help of scanning tunneling microscopy (STM) it has become possible to address single magnetic impurities on superconducting surfaces and to investigate the peculiar properties of the in-gap states known as Yu-Shiba-Rusinov (YSR) states. However, until very recently YSR states were only investigated with conventional tunneling spectroscopy, missing the crucial information contained in other transport properties such as shot noise. Here, we adapt the concept of full counting statistics (FCS) to provide a very deep insight into the spin-dependent transport in these hybrid systems. We illustrate the power of FCS by analyzing different situations in which YSR states show up including single-impurity junctions, as well as double-impurity systems where one can probe the tunneling between individual YSR states. The FCS concept allows us to unambiguously identify every tunneling process that plays a role in these situations. Moreover, FCS provides all the relevant transport properties, including current, shot noise and all the cumulants of the current distribution. Our approach can reproduce the experimental results recently reported on the shot noise of a single-impurity junction with a normal STM tip. We also predict the signatures of resonant (and non-resonant) multiple Andreev reflections in the shot noise of single-impurity junctions with two superconducting electrodes. In the case of double-impurity junctions we show that the direct tunneling between YSR states is characterized by a strong reduction of the Fano factor that reaches a minimum value of 7/32, a new fundamental result in quantum transport. The FCS approach presented here can be naturally extended to investigate the spin-dependent superconducting transport in a variety of situations, and it is also suitable to analyze multi-terminal superconducting junctions, irradiated contacts, and many other basic situations.

Flux fractionalization transition in anisotropic $S=1$ antiferromagnets and dimer-loop models. (arXiv:2305.07012v2 [cond-mat.stat-mech] UPDATED)
Souvik Kundu, Kedar Damle

We demonstrate that the low temperature ($T$) properties of a class of anisotropic spin $S=1$ kagome (planar pyrochlore) antiferromagnets on a field-induced $\frac{1}{3}$-magnetization ($\frac{1}{2}$-magnetization) plateau are described by a model of fully-packed dimers and loops on the honeycomb (square) lattice, with a temperature-dependent relative fugacity $w(T)$ for the dimers. The fully-packed O(1) loop model ($w=0$) and the fully-packed dimer model ($w=\infty$) limits of this dimer-loop model are found to be separated by a phase transition at a finite and nonzero critical fugacity $w_c$, with interesting consequences for the spin correlations of the frustrated magnet. The $w>w_c$ phase has short loops and spin correlations dominated by power-law columnar order (with subdominant dipolar correlations), while the $w<w_c$ phase has dominant dipolar spin correlations and long loops governed by a power-law distribution of loop sizes. Away from $w_c$, both phases are described by a long-wavelength Gaussian effective action for a scalar height field that represents the coarse-grained electrostatic potential of fluctuating dipoles. The destruction of power-law columnar spin order below $w_c$ is driven by an unusual {\em flux fractionalization} mechanism, topological in character but quite distinct from the usual Kosterlitz-Thouless mechanism for such transitions: Fractional electric fluxes which are bound into integer values for $w>w_c$, proliferate in the $w<w_c$ phase and destroy power-law columnar order.

Control of wave scattering for robust coherent transmission in a disordered medium. (arXiv:2305.07831v3 [physics.optics] UPDATED)
Zhun-Yong Ong

The spatial structure of the inhomogeneity in a disordered medium determines how waves scatter and propagate in it. We present a theoretical model of how the Fourier components of the disorder control wave scattering in a two-dimensional disordered medium, by analyzing the disordered Green's function for scalar waves. By selecting a set of Fourier components with the appropriate wave vectors, we can enhance or suppress wave scattering to filter out unwanted waves and allow the robust coherent transmission of waves at specific angles and wavelengths through the disordered medium. Based on this principle, we propose an approach for creating selective transparency, band gaps and anisotropy in disordered media. This approach is validated by direct numerical simulations of coherent wave transmission over a wide range of incident angles and frequencies and can be experimentally realized in disordered photonic crystals. Our approach, which requires neither nontrivial topological wave properties nor a non-Hermitian medium, creates opportunities for exploring a broad range of wave phenomena in disordered systems.

The Underlying Scaling Laws and Universal Statistical Structure of Complex Datasets. (arXiv:2306.14975v2 [cs.LG] UPDATED)
Noam Levi, Yaron Oz

We study universal traits which emerge both in real-world complex datasets, as well as in artificially generated ones. Our approach is to analogize data to a physical system and employ tools from statistical physics and Random Matrix Theory (RMT) to reveal their underlying structure. We focus on the feature-feature covariance matrix, analyzing both its local and global eigenvalue statistics. Our main observations are: (i) The power-law scalings that the bulk of its eigenvalues exhibit are vastly different for uncorrelated normally distributed data compared to real-world data, (ii) this scaling behavior can be completely modeled by generating gaussian data with long range correlations, (iii) both generated and real-world datasets lie in the same universality class from the RMT perspective, as chaotic rather than integrable systems, (iv) the expected RMT statistical behavior already manifests for empirical covariance matrices at dataset sizes significantly smaller than those conventionally used for real-world training, and can be related to the number of samples required to approximate the population power-law scaling behavior, (v) the Shannon entropy is correlated with local RMT structure and eigenvalues scaling, and substantially smaller in strongly correlated datasets compared to uncorrelated synthetic data, and requires fewer samples to reach the distribution entropy. These findings show that with sufficient sample size, the Gram matrix of natural image datasets can be well approximated by a Wishart random matrix with a simple covariance structure, opening the door to rigorous studies of neural network dynamics and generalization which rely on the data Gram matrix.

Orbital Multiferroicity in Pentalayer Rhombohedral Graphene. (arXiv:2308.08837v2 [cond-mat.mes-hall] UPDATED)
Tonghang Han, Zhengguang Lu, Giovanni Scuri, Jiho Sung, Jue Wang, Tianyi Han, Kenji Watanabe, Takashi Taniguchi, Liang Fu, Hongkun Park, Long Ju

Ferroic orders describe spontaneous polarization of spin, charge, and lattice degrees of freedom in materials. Materials featuring multiple ferroic orders, known as multiferroics, play important roles in multi-functional electrical and magnetic device applications. 2D materials with honeycomb lattices offer exciting opportunities to engineer unconventional multiferroicity, where the ferroic orders are driven purely by the orbital degrees of freedom but not electron spin. These include ferro-valleytricity corresponding to the electron valley and ferro-orbital-magnetism supported by quantum geometric effects. Such orbital multiferroics could offer strong valley-magnetic couplings and large responses to external fields-enabling device applications such as multiple-state memory elements, and electric control of valley and magnetic states. Here we report orbital multiferroicity in pentalayer rhombohedral graphene using low temperature magneto-transport measurements. We observed anomalous Hall signals Rxy with an exceptionally large Hall angle (tan{\Theta}H > 0.6) and orbital magnetic hysteresis at hole doping. There are four such states with different valley polarizations and orbital magnetizations, forming a valley-magnetic quartet. By sweeping the gate electric field E we observed a butterfly-shaped hysteresis of Rxy connecting the quartet. This hysteresis indicates a ferro-valleytronic order that couples to the composite field E\cdot B, but not the individual fields. Tuning E would switch each ferroic order independently, and achieve non-volatile switching of them together. Our observations demonstrate a new type of multiferroics and point to electrically tunable ultra-low power valleytronic and magnetic devices.

Symmetry dictated universal helicity redistribution of Dirac fermions in transport. (arXiv:2309.02474v2 [cond-mat.mes-hall] UPDATED)
Jun-Yin Huang, Rui-Hua Ni, Hong-Ya Xu, Liang Huang

Helicity is a fundamental property of Dirac fermions. Yet, the general rule of how it changes in transport is still lacking. We uncover, theoretically, the universal spinor state transformation and consequently helicity redistribution rule in two cases of transport through potentials of electrostatic and mass types, respectively. The former is dictated by Lorentz boost and its complex counterpart in Klein tunneling regime, which establishes miraculously a unified yet latent connection between helicity, Klein tunneling, and Lorentz boost. The latter is governed by an abstract rotation group we construct, which reduces to SO(2) when acting on the plane of effective mass and momentum. They generate invariant submanifolds, i.e., leaves, that foliate the Hilbert space of Dirac spinors. Our results provide a basis for unified understanding of helicity transport, and may open a new window for exotic helicity-based physics and applications in mesoscopic systems.

Relaxation terms for anomalous hydrodynamic transport in Weyl semimetals from kinetic theory. (arXiv:2309.05692v2 [hep-th] UPDATED)
Andrea Amoretti, Daniel K. Brattan, Luca Martinoia, Ioannis Matthaiakakis, Jonas Rongen

We consider as a model of Weyl semimetal thermoelectric transport a $(3+1)$-dimensional charged, relativistic and relaxed fluid with a $U(1)_{V} \times U(1)_{A}$ chiral anomaly. We take into account all possible mixed energy, momentum, electric and chiral charge relaxations, and discover which are compatible with electric charge conservation, Onsager reciprocity and a finite DC conductivity. We find that all relaxations respecting these constraints necessarily render the system open and violate the second law of thermodynamics. We then demonstrate how the relaxations we have found arise from kinetic theory and a modified relaxation time approximation. Our results lead to DC conductivities that differ from those found in the literature opening the path to experimental verification.

Second-order optical response of superconductors induced by supercurrent injection. (arXiv:2309.14077v2 [cond-mat.supr-con] UPDATED)
Linghao Huang, Jing Wang

We develop a theory of the nonlinear optical responses in superconducting systems in the presence of a dc supercurrent. The optical transitions between particle-hole pair bands across the superconducting gap are allowed in clean superconductors as the inversion-symmetry-breaking by supercurrent. Vertex correction is included in optical conductivity to maintain the $U(1)$ gauge symmetry in the mean-field formalism, which contains the contributions from collective modes. We show two pronounced current dependent peaks in the second-order nonlinear optical conductivity $\sigma^{(2)}(\omega)$ at the gap edge $2\hbar\omega=2\Delta$ and $\hbar\omega=2\Delta$, which diverge in the clean limit. We demonstrate this in the models of single-band superconductor with $s$-wave and $d$-wave pairings, and Dirac fermion systems with $s$-wave pairing. Our theory predicts the current induced peak in $\text{Im}[\sigma^{(2)}(\omega)]$ is proportional to square of the supercurrent density in the $s$-wave single-band model, with the same order of magnitude as the recent experimental observation of second-harmonic generation in NbN by Nakamura et al. [Phys. Rev. Lett. 125, 097004 (2020)]. The supercurrent induced nonlinear optical spectroscopy provides a valuable toolbox to explore novel superconductors.

Aspects of $T\bar{T}+J\bar{T }$ deformed 2D topological gravity : from partition function to late-time SFF. (arXiv:2309.16658v2 [hep-th] UPDATED)
Arpan Bhattacharyya, Saptaswa Ghosh, Sounak Pal

In this paper, we investigate different thermodynamic properties of $T\bar{T}+J\bar{T }$ deformed 2D-gravity. First, we compute the partition function of $U(1)$ coupled 2D-gravity with fixed chemical potential, obtained from the dimensional reduction of the four-dimensional Einstein-Maxwell theory. Then, we compute the partition function of the deformed theory and study the genus expansion of the one and two-point correlation function of the partition function of the theory. Subsequently, we use the one-point function to compute the ``Annealed'' and ``Quenched'' free energy in low-temperature limits and make a qualitative comparison with the undeformed theory. Then, using the two-point function, we compute the Spectral Form Factor of the deformed theory in early and late time. We find a dip and ramp structure in early and late time, respectively. We also get a plateau structure in the $\tau$-scaling limit. Last but not least, we comment on the late-time topology change to give a physical interpretation of the ramp of the Spectral Form Factor for our theory.

Found 5 papers in prb
Date of feed: Tue, 03 Oct 2023 03:17:07 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)

Dynamical effects on photoluminescence spectra from first principles: A many-body Green's function approach
Pierluigi Cudazzo
Author(s): Pierluigi Cudazzo

Coupling of excitations, arising from electronic correlation or electron-phonon interaction, leads to intriguing effects on the spectra of materials. Current approximations to calculate photoluminescence spectra most often describe this coupling insufficiently. Starting from basic equations of many-…

[Phys. Rev. B 108, 165101] Published Mon Oct 02, 2023

Quantum Monte Carlo simulations of thermodynamic properties of attractive $\mathrm{SU}(3)$ Dirac fermions
Xiang Li, Han Xu, and Yu Wang
Author(s): Xiang Li, Han Xu, and Yu Wang

We employ the determinant quantum Monte Carlo method to study the finite-temperature properties of the half-filled attractive $\mathrm{SU}(3)$ Hubbard model on a honeycomb lattice. We calculate the phase diagram in which the phase boundary separates the disordered phase and the charge density wave (…

[Phys. Rev. B 108, 165102] Published Mon Oct 02, 2023

Energy dissipation of a carbon monoxide molecule manipulated using a metallic tip on copper surfaces
Norio Okabayashi, Thomas Frederiksen, Alexander Liebig, and Franz J. Giessibl
Author(s): Norio Okabayashi, Thomas Frederiksen, Alexander Liebig, and Franz J. Giessibl

The manipulation process of a single CO molecule on a copper single crystal by a metallic tip is studied here using noncontact atomic force microscopy, with dissipation energy detection, vibrational spectroscopy, and density functional theory calculations. The manipulation of the CO molecule between the two adjacent top sites is found to occur via an intermediate state of CO on the bridging site. Furthermore, this finding allows for the interpretation of static and dynamic friction at the atomic scale.

[Phys. Rev. B 108, 165401] Published Mon Oct 02, 2023

Tunable nonlinear anisotropic Rashba splitting in monolayer transition metal dichalcogenide $\mathrm{Mo}{\mathrm{S}}_{2(1−x)}{\mathrm{Se}}_{2x}$ alloys
Souvick Chakraborty and Satyabrata Raj
Author(s): Souvick Chakraborty and Satyabrata Raj

We investigate the Rashba effect in thermodynamically stable nonpolar transition metal dichalcogenide (TMD) alloys of the form $\mathrm{Mo}{\mathrm{S}}_{2(1−x)}{\mathrm{Se}}_{2x}$ in the presence of an out-of-plane electric field using first-principles calculations. These alloys exhibit a nonlinear …

[Phys. Rev. B 108, 165402] Published Mon Oct 02, 2023

Skyrmion lattice annihilation by point defects in the multiferroic ${\mathrm{Cu}}_{2}{\mathrm{OSeO}}_{3}$
Houssam Sabri and Igor Kornev
Author(s): Houssam Sabri and Igor Kornev

First-principles-based effective Hamiltonian simulations are used to reveal the hidden connection between various topological defects, namely point defects and skyrmions, in copper oxide selenite (${\mathrm{Cu}}_{2}{\mathrm{OSeO}}_{3}$). Using this approach, we show that (i) ${\mathrm{Cu}}_{2}{\math…

[Phys. Rev. B 108, L140401] Published Mon Oct 02, 2023

Found 1 papers in prl
Date of feed: Tue, 03 Oct 2023 03:17:08 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)

Impact of Optically Pumped Nonequilibrium Steady States on Luminescence Emission of Atomically Thin Semiconductor Excitons
Manuel Katzer, Malte Selig, Dominik Christiansen, Mariana V. Ballottin, Peter C. M. Christianen, and Andreas Knorr
Author(s): Manuel Katzer, Malte Selig, Dominik Christiansen, Mariana V. Ballottin, Peter C. M. Christianen, and Andreas Knorr

The interplay of the nonequivalent corners in the Brillouin zone of transition metal dichalcogenides (TMDCs) has been investigated extensively. While experimental and theoretical works contributed to a detailed understanding of the relaxation of selective optical excitations and the related relaxati…

[Phys. Rev. Lett. 131, 146201] Published Mon Oct 02, 2023

Found 1 papers in acs-nano
Date of feed: Mon, 02 Oct 2023 13:07:51 GMT

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[ASAP] Direct Electrochemical Functionalization of Graphene Grown on Cu Including the Reaction Rate Dependence on the Cu Facet Type
Minhyeok Kim, Se Hun Joo, Meihui Wang, Sergey G. Menabde, Da Luo, Sunghwan Jin, Hyeongjun Kim, Won Kyung Seong, Min Seok Jang, Sang Kyu Kwak, Sun Hwa Lee, and Rodney S. Ruoff

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ACS Nano
DOI: 10.1021/acsnano.3c04138