Found 64 papers in cond-mat
Date of feed: Tue, 10 Oct 2023 00:30:00 GMT

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Observable signatures of Hall viscosity in lowest Landau level superfluids. (arXiv:2310.04495v1 [cond-mat.quant-gas])
Seth Musser, Hart Goldman, T. Senthil

Hall viscosity is a non-dissipative viscosity occurring in systems with broken time-reversal symmetry, such as quantum Hall phases and $p+ip$ superfluids. Despite Hall viscosity's expected ubiquity and past observations in classical soft matter systems, it has yet to be measured experimentally in any quantum phase of matter. Toward this end, we describe the observable effects of Hall viscosity in a simple family of rotating Bose-Einstein condensates of electrically neutral bosons, in which all of the bosons condense into a single LLL orbital. Such phases are accessible to current cold atom experiments, and we dub them lowest Landau level (LLL) superfluids. We demonstrate that LLL superfluids possess a non-universal Hall viscosity, leading to a range of observable consequences such as rotation of vortex-antivortex dipoles and wave-vector dependent corrections to the speed of sound. Furthermore, using a coherent state path integral approach, we present a microscopic derivation of the Landau-Ginzburg equations of a LLL superfluid, showing explicitly how Hall viscosity enters.


Giant Modulation of Refractive Index from Correlated Atomic-Scale Disorder. (arXiv:2310.04615v1 [cond-mat.mtrl-sci])
Boyang Zhao, Guodong Ren, Hongyan Mei, Vincent C. Wu, Shantanu Singh, Gwan-Yeong Jung, Huandong Chen, Raynald Giovine, Shanyuan Niu, Arashdeep S. Thind, Jad Salman, Nick S. Settineri, Bryan C. Chakoumakos, Michael E. Manley, Raphael P. Hermann, Andrew R. Lupini, Miaofang Chi, Jordan A. Hachtel, Arkadiy Simonov, Simon J. Teat, Raphaële J. Clément, Mikhail A. Kats, J. Ravichandran, Rohan Mishra

Correlated disorder has been shown to enhance and modulate magnetic, electrical, dipolar, electrochemical and mechanical properties of materials. However, the possibility of obtaining novel optical and opto-electronic properties from such correlated disorder remains an open question. Here, we show unambiguous evidence of correlated disorder in the form of anisotropic, sub-angstrom-scale atomic displacements modulating the refractive index tensor and resulting in the giant optical anisotropy observed in BaTiS3, a quasi-one-dimensional hexagonal chalcogenide. Single crystal X-ray diffraction studies reveal the presence of antipolar displacements of Ti atoms within adjacent TiS6 chains along the c-axis, and three-fold degenerate Ti displacements in the a-b plane. 47/49Ti solid-state NMR provides additional evidence for those Ti displacements in the form of a three-horned NMR lineshape resulting from low symmetry local environment around Ti atoms. We used scanning transmission electron microscopy to directly observe the globally disordered Ti a-b plane displacements and find them to be ordered locally over a few unit cells. First-principles calculations show that the Ti a-b plane displacements selectively reduce the refractive index along the ab-plane, while having minimal impact on the refractive index along the chain direction, thus resulting in a giant enhancement in the optical anisotropy. By showing a strong connection between correlated disorder and the optical response in BaTiS3, this study opens a pathway for designing optical materials with high refractive index and functionalities such as a large optical anisotropy and nonlinearity.


Transport Study of Charge Carrier Scattering in Monolayer WSe$_2$. (arXiv:2310.04624v1 [cond-mat.mes-hall])
Andrew Y. Joe, Kateryna Pistunova, Kristen Kaasbjerg, Ke Wang, Bumho Kim, Daniel A. Rhodes, Takashi Taniguchi, Kenji Watanabe, James Hone, Tony Low, Luis A. Jauregui, Philip Kim

Employing flux-grown single crystal WSe$_2$, we report charge carrier scattering behaviors measured in $h$-BN encapsulated monolayer field effect transistors. We perform quantum transport measurements across various hole densities and temperatures and observe an increase in transport mobility $\mu$ as a function of hole density in the degenerately doped sample. This unusual behavior can be explained by energy dependent scattering amplitude of strong defects calculated using the T-matrix approximation. Utilizing long mean-free path ($>$500 nm), we demonstrate the high quality of our electronic devices by showing quantized conductance steps from an electrostatically-defined quantum point contact. Our results show the potential for creating ultra-high quality quantum optoelectronic devices based on atomically thin semiconductors.


Giant 2D Skyrmion Topological Hall Effect with Ultrawide Temperature Window and Low-Current Manipulation in 2D Room-Temperature Ferromagnetic Crystals. (arXiv:2310.04663v1 [cond-mat.mtrl-sci])
Gaojie Zhang, Qingyuan Luo, Xiaokun Wen, Hao Wu, Li Yang, Wen Jin, Luji Li, Jia Zhang, Wenfeng Zhang, Haibo Shu, Haixin Chang

The discovery and manipulation of topological Hall effect (THE), an abnormal magnetoelectric response mostly related to the Dzyaloshinskii-Moriya interaction (DMI), are promising for next-generation spintronic devices based on topological spin textures such as magnetic skyrmions. However, most skyrmions and THE are stabilized in a narrow temperature window either below or over room temperature with high critical current manipulation. It is still elusive and challenging to achieve large THE with both wide temperature window till room temperature and low critical current manipulation. Here, by using controllable, naturally-oxidized, sub-20 and sub-10 nm 2D van der Waals room-temperature ferromagnetic Fe3GaTe2-x crystals, robust 2D THE with ultrawide temperature window ranging in three orders of magnitude from 2 to 300 K is reported, combining with giant THE of ~5.4 micro-ohm cm at 10 K and ~0.15 micro-ohm cm at 300 K which is 1-3 orders of magnitude larger than that of all known room-temperature 2D skyrmion systems. Moreover, room-temperature current-controlled THE is also realized with a low critical current density of ~6.2*10^5 A cm^-2. First-principles calculations unveil natural oxidation-induced highly-enhanced 2D interfacial DMI reasonable for robust giant THE. This work paves the way to room-temperature, electrically-controlled 2D THE-based practical spintronic devices.


Complexity and order in approximate quantum error-correcting codes. (arXiv:2310.04710v1 [quant-ph])
Jinmin Yi, Weicheng Ye, Daniel Gottesman, Zi-Wen Liu

We establish rigorous connections between quantum circuit complexity and approximate quantum error correction (AQEC) properties, covering both all-to-all and geometric scenarios including lattice systems. To this end, we introduce a type of code parameter that we call subsystem variance, which is closely related to the optimal AQEC precision. Our key finding is that if the subsystem variance is below an $O(k/n)$ threshold then any state in the code subspace must obey certain circuit complexity lower bounds, which identify nontrivial ``phases'' of codes. Based on our results, we propose $O(k/n)$ as a boundary between subspaces that should and should not count as AQEC codes. This theory of AQEC provides a versatile framework for understanding the quantum complexity and order of many-body quantum systems, offering new insights for wide-ranging physical scenarios, in particular topological order and critical quantum systems which are of outstanding importance in many-body and high energy physics. We observe from various different perspectives that roughly $O(1/n)$ represents a common, physically significant ``scaling threshold'' of subsystem variance for features associated with nontrivial quantum order.


Ultrafast Carrier Relaxation and Second Harmonic Generation in a Higher-Fold Weyl Fermionic System PtAl. (arXiv:2310.04717v1 [cond-mat.mes-hall])
Vikas Saini, Ajinkya Punjal, Utkarsh Kumar Pandey, Ruturaj Vikrant Puranik, Vikash Sharma, Vivek Dwij, Kritika Vijay, Ruta Kulkarni, Soma Banik, Aditya Dharmadhikari, Bahadur Singh, Shriganesh Prabhu, A. Thamizhavel

In topological materials, shielding of bulk and surface states by crystalline symmetries has provided hitherto unknown access to electronic states in condensed matter physics. Interestingly, photo-excited carriers relax on an ultrafast timescale, demonstrating large transient mobility that could be harnessed for the development of ultrafast optoelectronic devices. In addition, these devices are much more effective than topologically trivial systems because topological states are resilient to the corresponding symmetry-invariant perturbations. By using optical pump probe measurements, we systematically describe the relaxation dynamics of a topologically nontrivial chiral single crystal, PtAl. Based on the experimental data on transient reflectivity and electronic structures, it has been found that the carrier relaxation process involves both acoustic and optical phonons with oscillation frequencies of 0.06 and 2.94 THz, respectively, in picosecond time scale. PtAl with a space group of $P$$2_{1}$3 allows only one non-zero susceptibility element i.e. $d_{14}$, in second harmonic generation (SHG) with a large value of 468(1) pm/V, which is significantly higher than that observed in standard GaAs(111) and ZnTe(110) crystals. The intensity dependence of the SHG signal in PtAl reveals a non-perturbative origin. The present study on PtAl provides deeper insight into topological states which will be useful for ultrafast optoelectronic devices.


Manipulation of magnetic topological textures via perpendicular strain and polarization in van der Waals magnetoelectric heterostructure. (arXiv:2310.04810v1 [cond-mat.mtrl-sci])
Zhong Shen, Shuai Dong, Xiaoyan Yao

Multi-functional manipulation of magnetic topological textures such as skyrmions and bimerons in energy-efficient ways is of great importance for spintronic applications, but still being a big challenge. Here, by first-principles calculations and atomistic simulations, the creation and annihilation of skyrmions/bimerons, as key operations for the reading and writing of information in spintronic devices, are achieved in van der Waals magnetoelectric CrISe/In2Se3 heterostructure via perpendicular strain or electric field without external magnetic field. Besides, the bimeron-skyrmion conversion, size modulation and the reversible magnetization switching from in-plane to out-of-plane could also be realized in magnetic-field-free ways. Moreover, the topological charge and morphology can be precisely controlled by a small magnetic field. The strong Dzyaloshinskii-Moriya interaction and tunable magnetic anisotropy energy in a wide window are found to play vital roles in such energy efficient multi-functional manipulation, and the underlying physical mechanisms are elucidated. Our work predicts the CrISe/In2Se3 heterostructure being an ideal platform to address this challenge in spintronic applications, and theoretically guides the low-dissipation multi-functional manipulation of magnetic topological textures.


Non-Hermitian Topology and Flat Bands via an Exact Real Space Decimation Scheme. (arXiv:2310.04834v1 [cond-mat.mes-hall])
Ayan Banerjee, Arka Bandyopadhyay, Ronika Sarkar, Awadhesh Narayan

In recent years, non-Hermitian phases in classical and quantum systems have garnered significant attention. In particular, their intriguing band geometry offers a platform for exploring unique topological states and unconventional quantum dynamics. However, their topological characterization becomes particularly interesting and challenging in complex multiband systems. Here we propose a decimation framework, which leverages real space renormalization group to streamline the analysis of complex multiband non-Hermitian systems. Our systematic approach allows us to probe different phases and transitions, analyze bulk-boundary correspondence, formulate generalized Brillouin zones, investigate open boundary spectra, survey non-Bloch van Hove singularities, study disorder-induced effects, and explore tunable non-Hermitian flat band physics. Additionally, our framework allows proposing a hypothesis about quasi-one-dimensional bipartite non-Hermitian systems with flat bands, demonstrating their decoupling into Su-Schrieffer-Heeger chains and compact localized states across various models. Our work presents a powerful and comprehensive framework for understanding the intricate properties of non-Hermitian multiband systems, offering insights into the evolving landscape of non-Hermitian topological physics.


Electronic transport through the phtalocyanine molecule in atomic contacts Co. (arXiv:2310.04902v1 [quant-ph])
Ali Jaafar, Tarek Khalil

The effect of magnetic STM-tip on electronic, magnetic and electronic transport properties through the molecule junction STM-tip-Co/CoPc/Co(111), has been investigated by mean of ab initio electronic structure calculations. The spin transition has been studied by varying the distance (passing from the tunneling regime to the contact regime) between the tip and the CoPc molecule in both configurations, parallel and anti-parallel. Our calculation shows that the transition of spin of the Co atom of CoPc molecule has led to a change of the sign of the Magneto-Resistance (MR). It is also shown that the characteristic I-V has been influenced by this spin-transition of central atom of CoPc molecule.


Entanglement transition in rod packings. (arXiv:2310.04903v1 [cond-mat.soft])
Yeonsu Jung, Thomas Plumb-Reyes, Hao-Yu Greg Lin, L. Mahadevan

Random packings of stiff rods are self-supporting mechanical structures stabilized by their geometrical and topological complexity. To understand why, we deploy X-ray computerized tomography to unveil the structure of the packing. This allows us to define and directly visualize the spatial variations in "entanglement," a mesoscopic field that characterizes the local average crossing number, a measure of the topological complexity of the packing. We show that the entanglement field has information that is distinct from the density, orientational order, and contact distribution of the packing. We find that increasing the aspect ratio of the constituent rods in a packing leads to an abrupt change in the entanglement, correlated with a sharp transition in the mechanical response of the packing. This leads to an entanglement phase diagram for the mechanical response of dense rod packings that is likely relevant for a broad range of problems that goes beyond our specific study.


Terahertz phonon engineering and spectroscopy with van der Waals heterostructures. (arXiv:2310.04939v1 [cond-mat.mes-hall])
Yoseob Yoon, Zheyu Lu, Can Uzundal, Ruishi Qi, Wenyu Zhao, Sudi Chen, Qixin Feng, Kenji Watanabe, Takashi Taniguchi, Michael F. Crommie, Feng Wang

Phononic engineering at GHz frequencies form the foundation of microwave acoustic filters, high-speed acousto-optic modulators, and quantum transducers. THz phononic engineering could lead to acoustic filters and modulators at higher bandwidth and speed, as well as quantum circuits operating at higher temperatures. It can also enable new ways to manipulate and control thermal transport, as THz acoustic phonons are the main heat carriers in nonmetallic solids. Despite its potential, methods for engineering THz phonons have been little explored due to the challenges of achieving the required material control at sub-nanometer precision and efficient phonon coupling at THz frequencies. Here, we demonstrate efficient generation, detection, and manipulation of THz phonons through precise integration of atomically thin layers in van der Waals heterostructures. We employ few-layer graphene as an ultrabroadband transducer, converting fs near-infrared pulses to broadband acoustic phonon pulses with spectral content up to 3 THz. A single layer of WSe$_2$ is used as a sensor, where high-fidelity readout is enabled by the exciton-phonon coupling and strong light-matter interactions. By combining these capabilities in a single van der Waals heterostructure and detecting responses to incident mechanical waves, we performed THz phononic spectroscopy, similar to conventional optical spectroscopy which detects responses to incident electromagnetic waves. We demonstrate high-Q THz phononic cavities using hBN stacks. We further show that a single layer of WSe$_2$ embedded in hBN can efficiently block the transmission of THz phonons. By comparing our measurements to a nanomechanical model, we obtain the important force constants at the heterointerfaces. Our results could enable THz phononic metamaterials based on van der Waals heterostructures, as well as novel routes for thermal engineering.


Real-space decomposition of $p$-wave Kitaev chain. (arXiv:2310.05006v1 [cond-mat.str-el])
D. K. He, E. S. Ma, Z. Song

We propose an extended Bogoliubov transformation in real space for spinless fermions, based on which a class of Kitaev chains of length $2N$ with zero chemical potential can be mapped to two independent Kitaev chains of length $N$. It provides an alternative way to investigate a complicated system from the result of relatively simple systems. We demonstrate the implications of this decomposition by a Su-Schrieffer-Heeger (SSH) Kitaev model, which supports rich quantum phases. The features of the system, including the groundstate topology and nonequilibrium dynamics, can be revealed directly from that of sub-Kitaev chains. Based on this connection, two types of Bardeen-Cooper-Schrieffer (BCS)-pair order parameters are introduced to characterize the phase diagram, showing the ingredient of two different BCS pairing modes. Analytical analysis and numerical simulations show that the real-space decomposition for the ground state still holds true approximately in presence of finite chemical potential in the gapful regions.


Shear-Induced Phase Behavior and Topological Defects in Two-Dimensional Crystals. (arXiv:2310.05094v1 [cond-mat.soft])
Federico Ghimenti, Misaki Ozawa, Giulio Biroli, Gilles Tarjus

We investigate through numerical simulations how a two-dimensional crystal yields and flows under an applied shear. We focus over a range that allows us to both address the response in the limit of an infinitesimal shear rate and describe the phase behavior of the system at a finite shear rate. In doing so, we carefully discuss the role of the topological defects and of the finite-size effects. We map out the whole phase diagram of the flowing steady state in the plane formed by temperature and shear rate. Shear-induced melting of the two-dimensional crystal is found to proceed in two steps: first, the solid loses long-range bond-orientational order and flows, even for an infinitesimal shear rate (in the thermodynamic limit). The resulting flowing hexatic phase then melts to a flowing, rather isotropic, liquid at a finite shear rate that depends on temperature. Finally, at a high shear rate, a third regime corresponding to a strongly anisotropic string-like flowing phase appears.


Pulsed-mode metalorganic vapor-phase epitaxy of GaN on graphene-coated c-sapphire for freestanding GaN thin films. (arXiv:2310.05127v1 [cond-mat.mtrl-sci])
Seokje Lee, Muhammad S. Abbas, Dongha Yoo, Keundong Lee, Tobiloba G. Fabunmi, Eunsu Lee, Imhwan Kim, Daniel Jang, Sangmin Lee, Jusang Lee, Ki-Tae Park, Changgu Lee, Miyoung Kim, Yun Seog Lee, Celesta S. Chang, Gyu-Chul Yi

We report the growth of high-quality GaN epitaxial thin films on graphene-coated c-sapphire substrates using pulsed-mode metalorganic vapor-phase epitaxy, together with the fabrication of freestanding GaN films by simple mechanical exfoliation for transferable light-emitting diodes (LEDs). High-quality GaN films grown on the graphene-coated sapphire substrates were easily lifted off using thermal release tape and transferred onto foreign substrates. Furthermore, we revealed that the pulsed operation of ammonia flow during GaN growth was a critical factor for the fabrication of high-quality freestanding GaN films. These films, exhibiting excellent single crystallinity, were utilized to fabricate transferable GaN LEDs by heteroepitaxially growing InxGa1-xN/GaN multiple quantum wells and a p-GaN layer on the GaN films, showing their potential application in advanced optoelectronic devices.


Realization of multiple topological states and topological phase transitions in (4,0) carbon nanotube derivatives. (arXiv:2310.05233v1 [cond-mat.mtrl-sci])
Yan Gao, Yu Du, Yun-Yun Bai, Weikang Wu, Qiang Wang, Yong Liu, Kai Liu, Zhong-Yi Lu

Exploring various topological states (TS) and topological phase transitions (TPT) has attracted great attention in condensed matter physics. However, so far, there is rarely a typical material system that can be used as a platform to study the TS and TPT as the system transforms from one-dimensional (1D) nanoribbons to two-dimensional (2D) sheet then to three-dimensional (3D) bulk. Here, we first propose that some typical TS in 1D, 2D, and 3D systems can be realized in a tight-binding (TB) model. Following the TB model and further based on first-principles electronic structure calculations, we demonstrate that the structurally stable (4,0) carbon nanotube derivatives are an ideal platform to explore the semiconductor/nodal-point semimetal states in 1D nanoribbons [1D-(4,0)-C16H4 and 1D-(4,0)-C32H4], nodal-ring semimetal state in 2D sheet [2D-(4,0)-C16], and nodal-cage semimetal state in 3D bulk [3D-(4,0)-C16]. Furthermore, we calculate the characteristic band structures and the edge/surface states of 2D-(4,0)-C16 and 3D-(4,0)-C16 to confirm their nontrivial topological properties. Our work not only provides new excellent 2D and 3D members for the topological carbon material family, but also serves as an ideal template for the study of TS and TPT with the change of system dimension.


Comparison of different thermostats in the Holstein model. (arXiv:2310.05277v1 [cond-mat.stat-mech])
N. Fialko, M. Olshevets, V.D. Lakhno

When modeling charge dynamics in a chain of N sites at a temperature T, a Langevin thermostat and a Hamiltonian system, i.e., a chain heated to a given temperature before charge is injected, are compared. It is shown that the polaron disruption occurs in the same range of values of the thermal energy NT, however, T is not given by the initial data, but obtained after simulation from the average kinetic energy. For large T, the results averaged over a set of trajectories in a system with a Langevin thermostat and the results averaged over time for a Hamiltonian system are close, which does not contradict the Ergodic hypothesis.


Pressure-driven homogenization of lithium disilicate glasses. (arXiv:2310.05278v1 [cond-mat.mtrl-sci])
Yasser Bakhouch, Silvio Buchner, Rafael Abel Silveira, Leonardo Resende, Altair Soria Pereira, Abdellatif Hasnaoui, Achraf Atila

Lithium disilicate glasses and glass-ceramics are good potential candidates for biomedical applications and solid-state batteries, and serve as models of nucleation and crystal growth. Moreover, these glasses exhibit a phase separation that influences their nucleation and crystallization behavior. The atomistic mechanisms of the phase separation and their pressure dependence are unclear so far. Here, we used molecular dynamics simulations supported by experiments to assess the spatial heterogeneity of lithium disilicate glasses prepared under pressure. We show that the glass heterogeneity decreases with increasing the cooling pressure and almost disappears at pressures around 30 GPa. The origin of the heterogeneity is due to the attraction between Li cations to form clustering channels, which decreases with pressure. Through our results, we hope to provide valuable insights and guidance for making glass-ceramics with controlled crystallization.


Combining the D3 dispersion correction with the neuroevolution machine-learned potential. (arXiv:2310.05279v1 [cond-mat.mtrl-sci])
Penghua Ying, Zheyong Fan

Machine-learned potentials (MLPs) have become a popular approach of modelling interatomic interactions in atomistic simulations, but to keep the computational cost under control, a relatively short cutoff must be imposed, which put serious restrictions on the capability of the MLPs for modelling relatively long-ranged dispersion interactions. In this paper, we propose to combine the neuroevolution potential (NEP) with the popular D3 correction to achieve a unified NEP-D3 model that can simultaneously model relatively short-ranged bonded interactions and relatively long-ranged dispersion interactions. We show the improved descriptions of the binding and sliding energies in bilayer graphene can be obtained by the NEP-D3 approach compared to the pure NEP approach. We implement the D3 part into the GPUMD package such that it can be used out of the box for many exchange-correlation functionals. As a realistic application, we show that dispersion interactions result in approximately a 10% reduction in thermal conductivity for three typical metal-organic frameworks.


Surface ferromagnetism in rhombohedral heptalayer graphene moire superlattice. (arXiv:2310.05319v1 [cond-mat.mes-hall])
Wenqiang Zhou, Jing Ding, Jiannan Hua, Le Zhang, Kenji Watanabe, Takashi Taniguchi, Wei Zhu, Shuigang Xu

The topological electronic structure of crystalline materials often gives rise to intriguing surface states, such as Dirac surface states in topological insulators, Fermi arc surface states in Dirac semimetals, and topological superconductivity in iron-based superconductors. Recently, rhombohedral multilayer graphene has emerged as a promising platform for exploring exotic surface states due to its hosting of topologically protected surface flat bands at low energy, with the layer-dependent energy dispersion. These flat bands can promote electron correlations, leading to a plethora of quantum phenomena, including spontaneous symmetry breaking, superconductivity, ferromagnetism, and topological Chern insulators. Nevertheless, the intricate connection between the surface flat bands in rhombohedral multilayer graphene and the highly dispersive high-energy bands hinders the exploration of correlated surface states. Here, we present a method to isolate the surface flat bands of rhombohedral heptalayer (7L) graphene by introducing moire superlattices. The pronounced screening effects observed in the moire potential-modulated rhombohedral 7L graphene indicate its essential three-dimensional (3D) nature. The isolated surface flat bands favor correlated states on the surface in the regions away from charge-neutrality points. Most notably, we observe tunable surface ferromagnetism, manifested as an anomalous Hall effect with hysteresis loops, which is achieved by polarizing surface states using finite displacement fields. Our work establishes rhombohedral multilayer graphene moire superlattice as a unique 3D system for exploring correlated surface states.


The rotating excitons in two-dimensional materials: Valley Zeeman effect and chirality. (arXiv:2310.05335v1 [cond-mat.mes-hall])
Yu Cui, Xin-Jun Ma, Jia-Pei Deng, Shao-Juan Li, Ran-Bo Yang, Zhi-Qing Li, Zi-Wu Wang

We propose the rotational dynamics of the intralayer and interlayer excitons with their inherent momenta of inertia in the monolayer and bilayer transition metal dichalcogenides, respectively, where the new chirality of exciton is endowed by the rotational angular momentum, namely, the formations of left- and right-handed excitons at the +K and -K valleys, respectively. We find that angular momenta exchange between excitons and its surrounding phononic bath result in the large fluctuation of the effective g-factor and the asymmetry of valley Zeeman splitting observed in most recently experiments, both of which sensitively depend on the magnetic moments provided by the phononic environment. This rotating exciton model not only proposes a new controllable knob in valleytronics, but opens the door to explore the angular momentum exchange of the chiral quasiparticles with the many-body environment.


Quantum anomalous Hall state in a fluorinated 1T-MoSe$_2$ monolayer. (arXiv:2310.05356v1 [cond-mat.mes-hall])
Zhen Zhang, Zhichao Zhou, Xiaoyu Wang, Huiqian Wang, Xiuling Li, Xiao Li

The quantum anomalous Hall state with a large band gap and a high Chern number is significant for practical applications in spintronics. By performing first-principles calculations, we investigate electronic properties of the fully fluorinated 1T-MoSe$_{2}$ monolayer. Without considering the spin-orbit coupling, the band structure demonstrates single-spin semi-metallic properties and the trigonal warping around $K_{\pm}$ valleys. The introduction of the spin-orbit coupling opens considerable band gaps of $117.2$ meV around the two valleys, leading to a nontrivial quantum anomalous Hall state with a Chern number of $|C|=2$, which provides two chiral dissipationless transport channels from topological edge states and associated quantized anomalous Hall conductivity. In addition, an effective model is constructed to describe the low-energy physics of the monolayer. Our findings in the MoSe$_{2}$F$_{2}$ monolayer sheds light on large-gap quantum anomalous Hall states in two-dimensional materials with the chemical functionalization, and provides opportunities in designing low-power and noise-tolerant spintronic devices.


Moir\'e Semiconductors on Twisted Bilayer Dice Lattice. (arXiv:2310.05403v1 [cond-mat.mes-hall])
Di Ma, Yu-Ge Chen, Yue Yu, Xi Luo

We propose an effective lattice model for the Moir\'e structure of twisted bilayer dice lattice. We find that there are flat bands near zero energy level at any twist angle besides the magic ones. The flat bands contain both bands with zero Chern number which are originated from the destructive interference of the dice lattice and the topological non-trivial ones at the magic angle. The existence of the flat bands can be detected from the peak-splitting fine structure of the optical conductance at all angles, while the transition peaks do not split and only occur at magic angles in twisted bilayer graphene.


Observation of universal Kibble-Zurek scaling in an atomic Fermi superfluid. (arXiv:2310.05437v1 [cond-mat.quant-gas])
Kyuhwan Lee, Sol Kim, Taehoon Kim, Yong-il Shin

Half a century ago, T. Kibble proposed a scenario for topological defect formation from symmetry breaking during the expansion of the early Universe. W. Zurek later crystallized the concept to superfluid helium, predicting a power-law relation between the number of quantum vortices and the rate at which the system passes through the lambda transition. Here, we report the observation of Kibble-Zurek scaling in a homogeneous, strongly interacting Fermi gas undergoing a superfluid phase transition. We investigate the superfluid transition using two distinct control parameters: temperature and interaction strength. The microscopic physics of condensate formation is markedly different for the two quench parameters, signaled by their two orders of magnitude difference in the condensate formation timescale. However, regardless of the thermodynamic direction in which the system passes through a phase transition, the Kibble-Zurek exponent is identically observed to be about 0.68 and shows good agreement with theoretical predictions that describe superfluid phase transitions. This work demonstrates the gedanken experiment Zurek proposed for liquid helium that shares the same universality class with strongly interacting Fermi gases.


Control of valley optical conductivity and topological phases in buckled hexagonal lattice by orientation of in-plane magnetic field. (arXiv:2310.05439v1 [cond-mat.mes-hall])
Phusit Nualpijit, Bumned Soodchomshom

We investigate the optical conductivity, along with longitudinal and transverse conductivities, in buckled hexagonal lattice such as silicene subjected to both an in-plane magnetic field and a perpendicular electric field. In this model, we neglect the effect of the spin-orbit interaction, which is of a smaller order compared to the strong staggered potential and the next-nearest hoping energy. The orientations of the in-plane magnetic field and the perpendicular electric field give rise to a non-uniform, tunable gap. The Chern number for each valley degree of freedom deviates from being constant but remains steady when summed over the entire Brillouin zone. The longitudinal and transverse currents, in the case of a specific valley, can be selected by adjusting the direction of the electric field in the semimetal phase. Furthermore, the defining characteristics of topological phases induces the rapid change in longitudinal conductivity when varying the angle of orientation of the in-plane magnetic field under monochromatic light, and perfect valley filtering in transverse conductivity. The transverse current associated with a specific valley can be selected when the angle of orientation satisfies the specific conditions. This investigation paves the way for materials design with valley-locked current, using a specific orientation of the in-plane magnetic field.


Generalized Landauer bound from absolute irreversibility. (arXiv:2310.05449v1 [cond-mat.stat-mech])
Lorenzo Buffoni, Francesco Coghi, Stefano Gherardini

In this work, we introduce a generalization of the Landauer bound for erasure processes that stems from absolutely irreversible dynamics. Assuming that the erasure process is carried out in an absolutely irreversible way so that the probability of observing some trajectories is zero in the forward process but finite in the reverse process, we derive a generalized form of the bound for the average erasure work, which is valid also for imperfect erasure and asymmetric bits. The generalized bound obtained is tighter or, at worst, as tight as existing ones. Our theoretical predictions are supported by numerical experiments and the comparison with data from previous works.


Band structures of strained Kagome lattices. (arXiv:2310.05455v1 [cond-mat.mes-hall])
Luting Xu, Fan Yang

Materials with kagome lattice have attracted significant research attention due to their nontrivial features in energy bands. In this work, we theoretically investigate the evolution of electronic band structures of kagome lattice in response to uniaxial strain using both a tight-binding model and an antidot model based on a periodic muffin-tin potential. It is found that the Dirac points move with applied strain. Furthermore, the flat band of unstrained kagome lattice is found to develop into a highly anisotropic shape under a stretching strain along y direction, forming a partially flat band with a region dispersionless along ky direction while dispersive along kx direction. Our results shed light on the possibility of engineering the electronic band structures of kagome materials by mechanical strain.


Observation of Emergent Superconductivity in the Quantum Spin Hall Insulator Ta2Pd3Te5 via Pressure Manipulation. (arXiv:2310.05532v1 [cond-mat.mtrl-sci])
Hui Yu, Dayu Yan, Zhaopeng Guo, Yizhou Zhou, Xue Yang, Peiling Li, Zhijun Wang, Xiaojun Xiang, Junkai Li, Xiaoli Ma, Rui Zhou, Fang Hong, Yunxiao Wuli, Youguo Shi, Jian-Tao Wang, Xiaohui Yu

Quantum Spin Hall (QSH) insulators possess distinct helical in-gap states, enabling their edge states to act as one-dimensional conducting channels when backscattering is prohibited by time-reversal symmetry. However, it remains challenging to achieve high-performance combinations of nontrivial topological QSH states with superconductivity for applications and requires understanding of the complicated underlying mechanisms. Here, our experimental observations for a novel superconducting phase in the pressurized QSH insulator Ta2Pd3Te5 is reported, and the high-pressure phase maintains its original ambient pressure lattice symmetry up to 45 GPa. Our in-situ high-pressure synchrotron X-ray diffraction, electrical transport, infrared reflectance, and Raman spectroscopy measurements, in combination with rigorous theoretical calculations, provide compelling evidence for the association between the superconducting behavior and the abnormal densified phase. The isostructural transition was found to modify the topology of the Fermi surface directly, accompanied by a fivefold amplification of the density of states at 20 GPa compared to ambient pressure, which synergistically fosters the emergence of robust superconductivity. A profound comprehension of the fascinating properties exhibited by the compressed Ta2Pd3Te5 phase is achieved, highlighting the extraordinary potential of van der Waals (vdW) QSH insulators for exploring and investigating high-performance electronic advanced devices under extreme conditions.


Composition and optical properties of (In,Ga)As nanowires grown by group-III-assisted molecular beam epitaxy. (arXiv:2310.05582v1 [cond-mat.mtrl-sci])
M Gómez Ruiz, Aron Castro, Jesús Herranz, Alessandra da Silva, Achim Trampert, Oliver Brandt, Lutz Geelhaar, Jonas Lähnemann

(In,Ga) alloy droplets are used to catalyse the growth of (In,Ga)As nanowires by molecular beam epitaxy on Si(111) substrates. The composition, morphology and optical properties of these nanowires can be tuned by the employed elemental fluxes. To incorporate more than 10% of In, a high In/(In+Ga) flux ratio above 0.7 is required. We report a maximum In content of almost 30% in bulk (In,Ga)As nanowires for an In/(In+Ga) flux ratio of 0.8. However, with increasing In/(In+Ga) fl ux ratio, the nanowire length and diameter are notably reduced. Using photoluminescence and cathodoluminescence spectroscopy on nanowires covered by a passivating (In,Al)As shell, two luminescence bands are observed. A significant segment of the nanowires shows homogeneous emission, with a wavelength corresponding to the In content in this segment, while the consumption of the catalyst droplet leads to a spectrally-shifted emission band at the top of the nanowires. The (In,Ga)As nanowires studied in this work provide a new approach for the integration of infrared emitters on Si platforms.


Mode-Shell correspondence, a unifying theory in topological physics -- Part I: Chiral number of zero-modes. (arXiv:2310.05656v1 [cond-mat.mes-hall])
Lucien Jezequel, Pierre Delplace

We propose a theory, that we call the \textit{mode-shell correspondence}, which relates the topological zero-modes localised in phase space to a \textit{shell} invariant defined on the surface forming a shell enclosing these zero-modes. We show that the mode-shell formalism provides a general framework unifying important results of topological physics, such as the bulk-edge correspondence, higher-order topological insulators, but also the Atiyah-Singer and the Callias index theories. In this paper, we discuss the already rich phenomenology of chiral symmetric Hamiltonians where the topological quantity is the chiral number of zero-dimensionial zero-energy modes. We explain how, in a lot of cases, the shell-invariant has a semi-classical limit expressed as a generalised winding number on the shell, which makes it accessible to analytical computations.


Quasi van der Waals Epitaxy of Rhombohedral-stacked Bilayer WSe2 on GaP(111) Heterostructure. (arXiv:2310.05660v1 [cond-mat.mes-hall])
Aymen Mahmoudi, Meryem Bouaziz, Niels Chapuis, Geoffroy Kremer, Julien Chaste, Davide Romanin, Marco Pala, François Bertran, Patrick Le Fèvre, Iann C. Gerber, Gilles Patriarche, Fabrice Oehler, Xavier Wallart, Abdelkarim Ouerghi

The growth of bilayers of two-dimensional (2D) materials on conventional 3D semiconductors results in 2D/3D hybrid heterostructures, which can provide additional advantages over more established 3D semiconductors while retaining some specificities of 2D materials. Understanding and exploiting these phenomena hinge on knowing the electronic properties and the hybridization of these structures. Here, we demonstrate that rhombohedral-stacked bilayer (AB stacking) can be obtained by molecular beam epitaxy growth of tungsten diselenide (WSe2) on gallium phosphide (GaP) substrate. We confirm the presence of 3R-stacking of the WSe2 bilayer structure using scanning transmission electron microscopy (STEM) and micro-Raman spectroscopy. Also, we report high-resolution angle-resolved photoemission spectroscopy (ARPES) on our rhombohedral-stacked WSe2 bilayer grown on GaP(111)B substrate. Our ARPES measurements confirm the expected valence band structure of WSe2 with the band maximum located at the gamma point of the Brillouin zone. The epitaxial growth of WSe2 on GaP(111)B heterostructures paves the way for further studies of the fundamental properties of these complex materials, as well as prospects for their implementation in devices to exploit their promising electronic and optical properties.


Secondary proximity effect in a side-coupled double quantum dot structure. (arXiv:2310.05663v1 [cond-mat.mes-hall])
Jia-Ning Wang, Yong-Chen Xiong, Wang-Huai Zhou, Tan Peng, Ziyu Wang

Semiconductor quantum dots in close proximity to superconductors may provoke localized bound states within the superconducting energy gap known as Yu-Shiba-Rusinov (YSR) state, which is a promising candidate for constructing Majorana zero modes and topological qubits. Side-coupled double quantum dot systems are ideal platforms revealing the secondary proximity effect. Numerical renormalization group calculations show that, if the central quantum dot can be treated as a noninteracting resonant level, it acts as a superconducting medium due to the ordinary proximity effect. The bound state in the side dot behaves as the case of a single impurity connected to two superconducting leads. The side dot undergoes quantum phase transitions between a singlet state and a doublet state as the Coulomb repulsion, the interdot coupling strength, or the energy level sweeps. Phase diagrams indicate that the phase boundaries could be well illustrated by $\Delta \approx c {T_{K2}}$ in all cases, with $\Delta$ is the superconducting gap, $T_{K2}$ is the side Kondo temperature and $c$ is of the order $1.0$. These findings offer valuable insights into the secondary proximity effect, and show great importance for designing superconducting quantum devices.


Interplay of valley, layer and band topology towards interacting quantum phases in bilayer graphene moire superlattice. (arXiv:2310.05667v1 [cond-mat.mes-hall])
Yungi Jeong, Hangyeol Park, Taeho Kim, K. Watanabe, T. Taniguchi, Jeil Jung, Joonho Jang

A Bilayer of semiconducting 2D electronic systems has long been a versatile platform to study electronic correlation with tunable interlayer tunneling, Coulomb interactions and layer imbalance. In the natural graphite bilayer, Bernal-stacked bilayer graphene (BBG), the Landau level gives rise to an intimate connection between the valley and layer. Adding a moire superlattice potential enriches the BBG physics with the formation of topological minibands, potentially leading to tunable exotic quantum transports. Here, we present magnetotransport measurements of a high-quality bilayer graphene-hexagonal boron nitride (hBN) heterostructure. The zero-degree alignment generates a strong moire superlattice potential for the electrons in BBG and the resulting Landau fan diagram of longitudinal and Hall resistance displays a Hofstadter butterfly pattern with an unprecedented level of detail. We demonstrate that the intricate relationship between valley and layer degrees of freedom controls the topology of moire-induced bands, significantly influencing the energetics of interacting quantum phases in the BBG superlattice. We further observe signatures of field-induced correlated insulators and clear fractional quantizations of interaction driven topological quantum phases, such as fractional Chern insulators. Our results highlight the BBG/hBN heterostructure as an ideal platform for studying the delicate interplay between topology and electron correlation.


Visualizing delocalized quasiparticles in the vortex state of NbSe$_2$. (arXiv:2310.05716v1 [cond-mat.supr-con])
Jian-Feng Ge, Koen M. Bastiaans, Jiasen Niu, Tjerk Benschop, Maialen Ortego Larrazabal, Milan P. Allan

Bogoliubov quasiparticles play a crucial role in understanding the behavior of a superconductor at the nanoscale, particularly in a vortex lattice where they are thought to be confined to the vortex cores. Here, we use scanning tunneling noise microscopy, which can locally quantify quasiparticles by measuring the effective charge, to observe and image delocalized quasiparticles around vortices in NbSe$_2$ for the first time. Our data reveals a strong spatial variation of the quasiparticle concentration when tunneling into the vortex state. We find that quasiparticle poisoning dominates when vortices are less than four times the coherence length apart. Our results set a new length scale for quasiparticle poisoning in vortex-based Majorana qubits and yield information on the effect of vortices in quantum circuits. Finally, we can describe our findings within the Ginzburg-Landau framework, but the microscopic origin of the far-extending quasiparticles is yet to be understood.


Desalination Performance of Nano porous Mos$_2$ Membrane on Different Salts of Saline Water: A Molecular Dynamics Study. (arXiv:2310.05729v1 [cond-mat.soft])
A K M Monjur Morshed, Nudrat Nawal, Md Rashed Nizam, Priom Das

The freshwater crisis is a growing concern and a pressing problem for the world because of the increasing population, civilization, and rapid industrial growth. The water treatment facilities are able to supply less than 1% of the total water demand. Water desalination can be a potential solution to deal with this alarming issue. Researchers have been exploring for quite some time to find novel nano-enhanced membranes and manufacturing techniques to increase the efficiency of the desalination process. Graphene and graphene modified membranes showed huge potential as desalination membranes for comparatively easier synthesis process and higher ion rejection rate than conventional filter materials. Currently, single-layer Mos$_2$ has been discovered to have the same potential of water permeability and ion rejection rate as graphene membrane in a more energy-efficient way. For almost analogous nano porous structure of the graphene membrane, almost 70% of the higher water flux is obtained from the Mos$_2$ membrane. In this work, it has been shown that nano porous Mos$_2$ membranes provide a promising result for desalinating other salts of seawater alongside NaCl. We have also observed the effect of variations in ions, pore size, and pressure on water permeation and ion rejection rates in the water desalination process. In this study, water permeation increased significantly by increasing the pore area from 20{\AA} to 80{\AA}. The rate of water filtration increases in proportion to both applied pressure and pore size, sacrificing the ion rejection rate for the type of ions studied. A combination of salt ions in the saline water for desalination has also been studied, where the rejection rates for the different ions are separately represented for various applied pressures. For seawater, the Mos$_2$ membrane has showed quite promising performance in the study of ion variation.


Stability of fractional Chern insulators with a non-Landau level continuum limit. (arXiv:2310.05758v1 [cond-mat.str-el])
Bartholomew Andrews, Mathi Raja, Nimit Mishra, Michael Zaletel, Rahul Roy

The stability of fractional Chern insulators is widely believed to be predicted by the resemblance of their single-particle spectra to Landau levels. We investigate the scope of this geometric stability hypothesis by analyzing the stability of a set of fractional Chern insulators that explicitly do not have a Landau level continuum limit. By computing the many-body spectra of Laughlin states in a generalized Hofstadter model, we analyze the relationship between single-particle metrics, such as trace inequality saturation, and many-body metrics, such as the magnitude of the many-body and entanglement gaps. We show numerically that the geometric stability hypothesis holds for Chern bands that are not continuously connected to Landau levels, as well as conventional Chern bands, albeit often requiring larger system sizes to converge for these configurations.


2+1D symmetry-topological-order from local symmetric operators in 1+1D. (arXiv:2310.05790v1 [cond-mat.str-el])
Kansei Inamura, Xiao-Gang Wen

A generalized symmetry (defined by the algebra of local symmetric operators) can go beyond group or higher group description. A theory of generalized symmetry (up to holo-equivalence) was developed in terms of symmetry-TO -- a bosonic topological order (TO) with gappable boundary in one higher dimension. We propose a general method to compute the 2+1D symmetry-TO from the local symmetric operators in 1+1D systems. Our theory is based on the commutant patch operators, which are extended operators constructed as products and sums of local symmetric operators. A commutant patch operator commutes with all local symmetric operators away from its boundary. We argue that topological invariants associated with anyon diagrams in 2+1D can be computed as contracted products of commutant patch operators in 1+1D. In particular, we give concrete formulae for several topological invariants in terms of commutant patch operators. Topological invariants computed from patch operators include those beyond modular data, such as the link invariants associated with the Borromean rings and the Whitehead link. These results suggest that the algebra of commutant patch operators is described by 2+1D symmetry-TO. Based on our analysis, we also argue briefly that the commutant patch operators would serve as order parameters for gapped phases with finite symmetries.


Controlling Topology through Targeted Symmetry Manipulation in Magnetic Systems. (arXiv:2310.05896v1 [cond-mat.mes-hall])
Ilyoun Na, Marc Vila, Sinéad M. Griffin

The possibility of selecting magnetic space groups by orienting the magnetization direction or tuning magnetic orders offers a vast playground for engineering symmetry protected topological phases in magnetic materials. In this work, we study how selective tuning of symmetry and magnetism can influence and control the resulting topology in a 2D magnetic system, and illustrate such procedure in the ferromagnetic monolayer MnPSe$_3$. Density functional theory calculations reveals a symmetry-protected accidental semimetalic (SM) phase for out-of-plane magnetization which becomes an insulator when the magnetization is tilted in-plane, reaching band gap values close to $100$ meV. We identify an order-two composite antiunitary symmetry and threefold rotational symmetry that induce the band crossing and classify the possible topological phases using symmetry analysis, which we support with tight-binding and $\mathbf{k}\cdot\mathbf{p}$ models. Breaking of inversion symmetry opens a gap in the SM phase, giving rise to a Chern insulator. We demonstrate this explicitly in the isostructural Janus compound Mn$_2$P$_2$S$_3$Se$_3$, which naturally exhibits Rashba spin-orbit coupling that breaks inversion symmetry. Our results map out the phase space of topological properties of ferromagnetic transition metal phosphorus trichalcogenides and demonstrate the potential of the magnetization-dependent metal-to-insulator transition as a spin switch in integrated two-dimensional electronics.


Protected Fermionic Zero Modes in Periodic Gauge Fields. (arXiv:2310.05913v1 [cond-mat.mes-hall])
Vo Tien Phong, Eugene J. Mele

It is well-known that macroscopically-normalizable zero-energy wavefunctions of spin-$\frac{1}{2}$ particles in a two-dimensional inhomogeneous magnetic field are spin-polarized and exactly calculable with degeneracy equaling the number of flux quanta linking the whole system. Extending this argument to massless Dirac fermions subjected to magnetic fields that have \textit{zero} net flux but are doubly periodic in real space, we show that there exist \textit{only two} Bloch-normalizable zero-energy eigenstates, one for each spin flavor. This result is immediately relevant to graphene multilayer systems subjected to doubly-periodic strain fields, which at low energies, enter the Hamiltonian as periodic pseudo-gauge vector potentials. Furthermore, we explore various related settings including nonlinearly-dispersing band structure models and systems with singly-periodic magnetic fields.


When Superconductivity Crosses Over: From BCS to BEC. (arXiv:2208.01774v4 [cond-mat.supr-con] UPDATED)
Qijin Chen, Zhiqiang Wang, Rufus Boyack, Shuolong Yang, K. Levin

New developments in superconductivity, particularly through unexpected and often astonishing forms of superconducting materials, continue to excite the community and stimulate theory. It is now becoming clear that there are two distinct platforms for superconductivity through natural and synthetic materials. Indeed, the latter category has greatly expanded in the last decade or so, with the discoveries of new forms of superfluidity in artificial heterostructures and the exploitation of proximitization. The former category continues to surprise through the Fe-based pnictides and chalcogenides, and nickelates as well as others. It is the goal of this review to present this two-pronged investigation into superconductors, with a focus on those which we have come to understand belong somewhere between the BCS and Bose-Einstein condensation (BEC) regimes. We characterize in detail the nature of this ``crossover" superconductivity, which is to be distinguished from crossover superfluidity in atomic Fermi gases. In the process, we address the multiple ways of promoting a system out of the BCS and into the BCS-BEC crossover regime within the context of concrete experimental realizations. These involve natural materials, such as organic conductors, as well as artificial, mostly two-dimensional materials, such as magic-angle twisted bilayer and trilayer graphene, or gate-controlled devices, as well as one-layer and interfacial superconducting films. This work should be viewed as a celebration of BCS theory by showing that even though this theory was initially implemented with the special case of weak correlations in mind, it can in a very natural way be extended to treat the case of these more exotic strongly correlated superconductors.


Limits of the phonon quasi-particle picture at the cubic-to-tetragonal phase transition in halide perovskites. (arXiv:2211.08197v2 [cond-mat.mtrl-sci] UPDATED)
Erik Fransson, Petter Rosander, Fredrik Eriksson, J. Magnus Rahm, Terumasa Tadano, Paul Erhart

The soft modes associated with continuous-order phase transitions are associated with strong anharmonicity. This leads to the overdamped limit where the phonon quasi-particle picture can breakdown. However, this limit is commonly restricted to a narrow temperature range, making it difficult to observe its signature feature, namely the breakdown of the inverse relationship between the relaxation time and damping. Here we present a physically intuitive picture based on the relaxation times of the mode coordinate and its conjugate momentum, which at the instability approach infinity and the inverse damping factor, respectively. We demonstrate this behavior for the cubic-to-tetragonal phase transition of the inorganic halide perovskite CsPbBr$_3$ via molecular dynamics, and show that the overdamped region extends almost 200 K above the transition temperature. Further, we investigate how the dynamics of these soft phonon modes change when crossing the phase transition.


Moir\'e Superstructures in Marginally-Twisted NbSe$_2$ Bilayers. (arXiv:2212.06728v3 [cond-mat.mes-hall] UPDATED)
J. G. McHugh, V. V. Enaldiev, V.I. Fal'ko

The creation of moir\'e superlattices in twisted bilayers of two-dimensional crystals has been utilised to engineer quantum material properties in graphene and transition metal dichalcogenide (TMD) semiconductors. Here, we examine the structural relaxation and electronic properties in small-angle twisted bilayers of metallic NbSe$_2$. Reconstruction appears to be particularly strong for misalignment angles $\theta_P$ < 2.9$^o$ and $\theta_{AP}$ < 1.2$^o$ for parallel (P) and antiparallel (AP) orientation of monolayers' unit cells, respectively. Multiscale modelling reveals the formation of domains and domain walls with distinct stacking, for which density functional theory (DFT) calculations are used to map the shape of the bilayer Fermi surface and the relative phase of the CDW order in adjacent layers. We find a significant modulation of interlayer coupling across the moir\'e superstructure and the existence of preferred interlayer orientations of the CDW phase, necessitating the nucleation of CDW discommensurations at superlattice domain walls.


Tuning quantum paramagnetism and d-wave superconductivity in single-layer iron chalcogenides by chemical pressure. (arXiv:2212.13603v2 [cond-mat.supr-con] UPDATED)
Qiang Zou, Basu Dev Oli, Huimin Zhang, Tatsuya Shishidou, Daniel Agterberg, Michael Weinert, Lian Li

By substituting S into single-layer FeSe/SrTiO3, chemical pressure is applied to tune its paramagnetic state that is modeled as an incoherent superposition of spin-spiral states. The resulting electronic bands resemble an ordered checkerboard antiferromagnetic structure, consistent with angle-resolved photoemission spectroscopy measurements. Scanning tunneling spectroscopy reveals a gap evolving from U-shaped for FeSe to V-shaped for FeS with decreasing size, attributed to a d-wave superconducting state for which nodes emerge once the gap size is smaller than the effective spin-orbit coupling.


Enhancement of Second-Order Non-Hermitian Skin Effect by Magnetic Fields. (arXiv:2212.14691v2 [cond-mat.mes-hall] UPDATED)
Chang-An Li, Björn Trauzettel, Titus Neupert, Song-Bo Zhang

The non-Hermitian skin effect is a unique phenomenon in which an extensive number of eigenstates are localized at the boundaries of a non-Hermitian system. Recent studies show that the non-Hermitian skin effect is significantly suppressed by magnetic fields. In contrast, we demonstrate that the second-order skin effect (SOSE) is robust and can even be enhanced by magnetic fields. Remarkably, SOSE can also be induced by magnetic fields from a trivial non-Hermitian system that does not experience any skin effect at zero field. These properties are intimately related to to the persistence and emergence of topological line gaps in the complex energy spectrum in presence of magnetic fields. Moreover, we show that a magnetic field can drive a non-Hermitian system from a hybrid skin effect, where the first-order skin effect and SOSE coexist, to pure SOSE. Our results describe a qualitatively new magnetic field behavior of the non-Hermitian skin effect.


Dynamics of Rapidly Rotating Bose-Einstein Quantum Droplets. (arXiv:2302.07481v3 [cond-mat.quant-gas] UPDATED)
Szu-Cheng Cheng, Yu-Wen Wang, Wen-Hsuan Kuan

This work theoretically investigates \textcolor{black}{the stationary properties} and the dynamics of the rotating quantum liquid droplets confined in a two-dimensional symmetric anharmonic trap. Mimicking the quantum Hall systems, the modified Gross-Pitaevskii equation with the inclusion of the Lee-Huang-Yang nonlinear interaction is analytically solved, and the role of the Landau-level mixing effect is addressed. \textcolor{black}{Via controlling the nonlinear interaction and the rotation speed, the rotating quantum droplet with multiply quantized vortex can be created, and the preference of the energetically favored quantum states can be distinguished in the phase diagram. To better interpret the underlying physics of the phase singularities, a brief comparison of the rotating quantum droplet and the optical vortex is made. The investigation of the long-term evolution of the rotating quantum droplets confirms the stability of the quantum states. At certain rotation speeds, the multi-periodic trajectories and breathings provide evidence of the emergence of the collective excitation of the surface mode in the vortex state. For quantum droplets carrying multiply quantized vortex, the microscopic snapshots of the rotation field adjusted current density distribution show that the combined nonlinear interaction and the anharmonic trapping potential can provide the restoring force to lead the quantum droplet to a regular and stable revolution and reach the dynamic equilibrium, revealing the signature of the generation of superfluids in the new kind of low-dimensional quantum liquids.


Complex semiclassical theory for non-Hermitian quantum systems. (arXiv:2303.01525v3 [cond-mat.mes-hall] UPDATED)
Guang Yang, Yongkang Li, Yongxu Fu, Zhenduo Wang, Yi Zhang

Non-Hermitian quantum systems exhibit fascinating characteristics such as non-Hermitian topological phenomena and skin effect, yet their studies are limited by the intrinsic difficulties associated with their eigenvalue problems, especially in larger systems and higher dimensions. In Hermitian systems, the semiclassical theory has played an active role in analyzing spectrum, eigenstate, phase, transport properties, etc. Here, we establish a complex semiclassical theory applicable to non-Hermitian quantum systems by an analytical continuation of the physical variables such as momentum, position, time, and energy in the equations of motion and quantization condition to the complex domain. Further, we propose a closed-orbit scheme and physical meaning under such complex variables. We demonstrate that such a framework straightforwardly yields complex energy spectra and quantum states, topological phases and transitions, and even the skin effect in non-Hermitian quantum systems, presenting an unprecedented perspective toward nontrivial non-Hermitian physics, even with larger systems and higher dimensions.


Experimental evidence for Berry curvature multipoles in antiferromagnets. (arXiv:2303.03274v3 [cond-mat.mes-hall] UPDATED)
Soumya Sankar, Ruizi Liu, Xue-Jian Gao, Qi-Fang Li, Caiyun Chen, Cheng-Ping Zhang, Jiangchang Zheng, Yi-Hsin Lin, Kun Qian, Ruo-Peng Yu, Xu Zhang, Zi Yang Meng, Kam Tuen Law, Qiming Shao, Berthold Jäck

Berry curvature multipoles appearing in topological quantum materials have recently attracted much attention. Their presence can manifest in novel phenomena, such as nonlinear anomalous Hall effects (NLAHE). The notion of Berry curvature multipoles extends our understanding of Berry curvature effects on the material properties. Hence, research on this subject is of fundamental importance and may also enable future applications in energy harvesting and high-frequency technology. It was shown that a Berry curvature dipole can give rise to a 2nd order NLAHE in materials of low crystalline symmetry. Here, we demonstrate a fundamentally new mechanism for Berry curvature multipoles in antiferromagnets that are supported by the underlying magnetic symmetries. Carrying out electric transport measurements on the kagome antiferromagnet FeSn, we observe a 3rd order NLAHE, which appears as a transverse voltage response at the 3rd harmonic frequency when a longitudinal a.c. current drive is applied. Interestingly, this NLAHE is strongest at and above room temperature. We combine these measurements with a scaling law analysis, a symmetry analysis, model calculations, first-principle calculations, and magnetic Monte-Carlo simulations to show that the observed NLAHE is induced by a Berry curvature quadrupole appearing in the spin-canted state of FeSn. At a practical level, our study establishes NLAHE as a sensitive probe of antiferromagnetic phase transitions in other materials, such as moir\'e superlattices, two-dimensional van der Waal magnets, and quantum spin liquid candidates, that remain poorly understood to date. More broadly, Berry curvature multipole effects are predicted to exist for 90 magnetic point groups. Hence, our work opens a new research area to study a variety of topological magnetic materials through nonlinear measurement protocols.


Entanglement Resolution with Respect to Conformal Symmetry. (arXiv:2303.07724v2 [hep-th] UPDATED)
Christian Northe

Entanglement is resolved in conformal field theory (CFT) with respect to conformal families to all orders in the UV cutoff. To leading order, symmetry-resolved entanglement is connected to the quantum dimension of a conformal family, while to all orders it depends on null vectors. Criteria for equipartition between sectors are provided in both cases. This analysis exhausts all unitary conformal families. Furthermore, topological entanglement entropy is shown to symmetry-resolve the Affleck-Ludwig boundary entropy. Configuration and fluctuation entropy are analyzed on grounds of conformal symmetry.


Opacity of graphene independent of light frequency and polarization due to the topological charge of the Dirac points. (arXiv:2303.14549v2 [cond-mat.mes-hall] UPDATED)
Matheus S. M. de Sousa, Wei Chen

The opacity of graphene is known to be approximately given by the fine-structure constant $\alpha$ times $\pi$. We point out the fact that the opacity is roughly independent of the frequency and polarization of the light can be attributed to the topological charge of the Dirac points. As a result, one can literally see the topological charge by naked eyes from the opacity of graphene, and moreover it implies that the fine-structure constant is topologically protected. A similar analysis suggests that 3D topological insulator thin films of any thickness also have opacity $\pi\alpha$ in the infrared region owing to the topological surface states, indicating that one can see the surface states by naked eyes through an infrared lens. For 3D Dirac or Weyl semimetals, the optical absorption power is linear to the frequency in the infrared region, with a linearity given by the fine-structure constant and the topological charge of Weyl points.


Tuning the lattice thermal conductivity in van-der-Waals structures through rotational (dis)ordering. (arXiv:2304.06978v2 [cond-mat.mtrl-sci] UPDATED)
Fredrik Eriksson, Erik Fransson, Christopher Linderälv, Zheyong Fan, Paul Erhart

It has recently been demonstrated that MoS2 with irregular interlayer rotations can achieve an extreme anisotropy in the lattice thermal conductivity (LTC), which is for example of interest for applications in waste heat management in integrated circuits. Here, we show by atomic scale simulations based on machine-learned potentials that this principle extends to other two-dimensional materials including C and BN. In all three materials introducing rotational disorder drives the through-plane LTC to the glass limit, while the in-plane LTC remains almost unchanged compared to the ideal bulk materials. We demonstrate that the ultralow through-plane LTC is connected to the collapse of their transverse acoustic modes in the through-plane direction. Furthermore, we find that the twist angle in periodic moir\'e structures representing rotational order provides an efficient means for tuning the through-plane LTC that operates for all chemistries considered here. The minimal through-plane LTC is obtained for angles between 1 and 4 degree depending on the material, with the biggest effect in MoS2. The angular dependence is correlated with the degree of stacking disorder in the materials, which in turn is connected to the slip surface. This provides a simple descriptor for predicting the optimal conditions at which the LTC is expected to become minimal.


Efficient GW calculations via the interpolation of the screened interaction in momentum and frequency space: The case of graphene. (arXiv:2304.10810v2 [cond-mat.mtrl-sci] UPDATED)
Alberto Guandalini, Dario A. Leon, Pino D'Amico, Claudia Cardoso, Andrea Ferretti, Massimo Rontani, Daniele Varsano

The GW self-energy may become computationally challenging to evaluate because of frequency and momentum convolutions. These difficulties were recently addressed by the development of the multipole approximation (MPA) and the W-av methods: MPA accurately approximates full-frequency response functions using a small number of poles, while W-av improves the convergence with respect to the k-point sampling in 2D materials. In this work we (i) present a theoretical scheme to combine them, and (ii) apply the newly developed approach to the paradigmatic case of graphene. Our findings show an excellent agreement of the calculated QP band structure with angle resolved photoemission spectroscopy (ARPES) data. Furthermore, the computational efficiency of MPA and W-av allows us to explore the logarithmic renormalization of the Dirac cone. To this aim, we develop an analytical model, derived from a Dirac Hamiltonian, that we parameterize using ab-initio data. The comparison of the models obtained with PPA and MPA results highlights an important role of the dynamical screening in the cone renormalization.


Dynamics of parafermionic states in transport measurements. (arXiv:2305.08906v2 [cond-mat.mes-hall] UPDATED)
Ida E. Nielsen, Jens Schulenborg, Reinhold Egger, Michele Burrello

Advances in hybrid fractional quantum Hall (FQH)-superconductor platforms pave the way for realisation of parafermionic modes. We analyse signatures of these non-abelian anyons in transport measurements across devices with $\mathbb{Z}_6$ parafermions (PFs) coupled to an external electrode. Simulating the dynamics of these open systems by a stochastic quantum jump method, we show that a current readout over sufficiently long times constitutes a projective measurement of the fractional charge shared by two PFs. Interaction of these topological modes with the FQH environment, however, may cause poisoning events affecting this degree of freedom which we model by jump operators that describe incoherent coupling of PFs with FQH edge modes. We analyse how this gives rise to a characteristic three-level telegraph noise in the current, constituting a very strong signature of PFs. We discuss also other forms of poisoning and noise caused by interaction with fractional quasiparticles in the bulk of the Hall system. We conclude our work with an analysis of four-PF devices, in particular on how the PF fusion algebra can be observed in electrical transport experiments.


Foldy-Wouthuysen transformation and multiwave states of a graphene electron in external fields and free (2+1)-space. (arXiv:2305.11879v2 [cond-mat.mes-hall] UPDATED)
Alexander J. Silenko

The relativistic Foldy-Wouthuysen transformation is used for an advanced description of planar graphene electrons in external fields and free (2+1)-space. It is shown that the initial Dirac equation should by based on the usual $(4\times4)$ Dirac matrices but not on the reduction of matrix dimensions and the use of $(2\times2)$ Pauli matrices. The latter approach does not agree with the experiment. The spin of graphene electrons is not the one-value spin and takes the values $\pm1/2$. The exact Foldy-Wouthuysen Hamiltonian of a graphene electron in uniform and nonuniform magnetic fields is derived. The exact energy spectrum agreeing with the experiment and exact Foldy-Wouthuysen wave eigenfunctions are obtained. These eigenfunctions describe multiwave (structured) states in (2+1)-space. It is proven that the Hermite-Gauss beams exist even in the free space. In the multiwave Hermite-Gauss states, graphene electrons acquire nonzero effective masses dependent on a quantum number and move with group velocities which are less than the Fermi velocity. Graphene electrons in a static electric field also can exist in the multiwave Hermite-Gauss states defining non-spreading coherent beams. These beams can be accelerated and decelerated.


Modeling of experimentally observed topological defects inside bulk polycrystals. (arXiv:2305.16454v2 [cond-mat.mtrl-sci] UPDATED)
Siddharth Singh, He Liu, Rajat Arora, Robert M. Suter, Amit Acharya

A rigorous methodology is developed for computing elastic fields generated by experimentally observed defect structures within grains in a polycrystal that has undergone tensile extension. An example application is made using a near-field High Energy X-ray Diffraction Microscope measurement of a zirconium sample that underwent $13.6\%$ tensile extension from an initially well-annealed state. (Sub)grain boundary features are identified with apparent disclination line defects in them. The elastic fields of these features identified from the experiment are calculated.


Average Symmetry Protected Higher-order Topological Amorphous Insulators. (arXiv:2306.02246v2 [cond-mat.dis-nn] UPDATED)
Yu-Liang Tao, Jiong-Hao Wang, Yong Xu

While topological phases have been extensively studied in amorphous systems in recent years, it remains unclear whether the random nature of amorphous materials can give rise to higher-order topological phases that have no crystalline counterparts. Here we theoretically demonstrate the existence of higher-order topological insulators in two-dimensional amorphous systems that can host more than six corner modes, such as eight or twelve corner modes. Although individual sample configuration lacks crystalline symmetry, we find that an ensemble of all configurations exhibits an average crystalline symmetry that provides protection for the new topological phases. To characterize the topological phases, we construct two topological invariants. Even though the bulk energy gap in the topological phase vanishes in the thermodynamic limit, we show that the bulk states near zero energy are localized, as supported by the level-spacing statistics and inverse participation ratio. Our findings open an avenue for exploring average symmetry protected higher-order topological phases in amorphous systems without crystalline counterparts.


Flat bands and magnetism in $\mathrm{\mathbf{Fe_4 Ge Te_2}}$ and $\mathrm{\mathbf{Fe_5GeTe_2}}$ due to bipartite crystal lattices. (arXiv:2306.15996v3 [cond-mat.mtrl-sci] UPDATED)
Fuyi Wang, Haijun Zhang

$\mathrm{Fe_{n=4,5}GeTe_2}$ exhibits quasi-two-dimensional properties as a promising candidate for a near-room-temperature ferromagnet, which has attracted great interest. In this work, we notice that the crystal lattice of $\mathrm{Fe_{n=4,5}GeTe_2}$ can be approximately regarded as being stacked by three bipartite crystal lattices. By combining the model Hamiltonians of bipartite crystal lattices and first-principles calculations, we investigate the electronic structure and the magnetism of $\mathrm{Fe_{n=4,5}GeTe_2}$. We conclude that flat bands near the Fermi level originate from the bipartite crystal lattices and that these flat bands are expected to lead to the itinerant ferromagnetism in $\mathrm{Fe_{n=4,5}GeTe_2}$. Interestingly, we also find that the magnetic moment of the Fe5 atom in $\mathrm{Fe_5 Ge Te_2}$ is distinct from the other Fe atoms and is sensitive to the Coulomb interaction $U$ and external pressure. These findings may be helpful to understand the exotic magnetic behavior of $\mathrm{Fe_{n=4,5} Ge Te_2}$.


Scaling of entanglement entropy at quantum critical points in random spin chains. (arXiv:2307.00062v2 [cond-mat.dis-nn] UPDATED)
Prashant Kumar, R. N. Bhatt

We study the scaling properties of the entanglement entropy (EE) near quantum critical points in interacting random antiferromagnetic (AF) spin chains. Using density-matrix renormalization group, we compute the half-chain EE near the topological phase transition between Haldane and Random Singlet phases in a disordered spin-1 chain. It is found to diverge logarithmically in system size with an effective central charge $c_{\rm eff} = 1.17(4)$ at the quantum critical point (QCP). Moreover, a scaling analysis of EE yields the correlation length exponent $\nu=2.28(5)$. Our unbiased calculation establishes that the QCP is in the universality class of the infinite-randomness fixed point predicted by previous studies based on strong disorder renormalization group technique. However, in the disordered spin-1/2 Majumdar-Ghosh chain, where a valence bond solid phase is unstable to disorder, the crossover length exponent obtained from a scaling analysis of EE disagrees with the expectation based on Imry-Ma argument. We provide a possible explanation.


Bilayer Kagome Borophene with Multiple van Hove Singularities. (arXiv:2307.07137v2 [cond-mat.mtrl-sci] UPDATED)
Qian Gao, Qimin Yan, Zhenpeng Hu, Lan Chen

The appearance of van Hove singularities near the Fermi level leads to prominent phenomena, including superconductivity, charge density wave, and ferromagnetism. Here a bilayer Kagome lattice with multiple van Hove singularities is designed and a novel borophene with such lattice (BK-borophene) is proposed by the first-principles calculations. BK-borophene, which is formed via three-center two-electron (3c-2e) sigma-type bonds, is predicted to be energetically, dynamically, thermodynamically, and mechanically stable. The electronic structure hosts both conventional and high-order van Hove singularities in one band. The conventional van Hove singularity resulting from the horse saddle is 0.065 eV lower than the Fermi level, while the high-order one resulting from the monkey saddle is 0.385 eV below the Fermi level. Both the singularities lead to the divergence of electronic density of states. Besides, the high-order singularity is just intersected to a Dirac-like cone, where the Fermi velocity can reach 1340000 m/s. The interaction between the two Kagome lattices is critical for the appearance of high-order van Hove singularities. The novel bilayer Kagome borophene with rich and intriguing electronic structure offers an unprecedented platform for studying correlation phenomena in quantum material systems and beyond.


Chiral topological whispering gallery modes formed by gyromagnetic photonic crystals. (arXiv:2307.12495v2 [physics.optics] UPDATED)
Yongqi Chen, Nan Gao, Guodong Zhu, Yurui Fang

We explore a hexagonal cavity that supports chiral topological whispering gallery (CTWG) modes, formed by a gyromagnetic photonic crystal. This mode is a special type of topologically protected optical mode that can propagate in photonic crystals with chiral direction. Finite element method simulations show that discrete edge states exist in the topological band gap due to the coupling of chiral edge states and WG modes. Since the cavity only supports edge state modes with group velocity in only one direction, it can purely generate traveling modes and be immune to interference modes. In addition, we introduced defects and disorder to test the robustness of the cavity, demonstrating that the CTWG modes can be effectively maintained under all types of perturbations. Our topological cavity platform offers useful prototype of robust topological photonic devices. The existence of this mode can have important implications for the design and application of optical devices.


Unconventional optical response in monolayer graphene upon dominant intraband scattering. (arXiv:2307.15945v3 [cond-mat.mes-hall] UPDATED)
Palash Saha, Bala Murali Krishna Mariserla

Scattering dynamics influence the graphenes transport properties and inhibits the charge carrier deterministic behaviour. The intra or inter-band scattering mechanisms are vital for graphenes optical conductivity response under specific considerations of doping. Here, we investigated the influence of scattering systematically on optical conductivity using a semi-classical multiband Boltzmann equation with inclusion of both electron-electron $\&$ electron-phonon collisions. We found unconventional characteristics of linear optical response with a significant deviation from the universal conductivity $\frac{e$^2$}{2$\hbar$}$ in doped monolayer graphene. This is explained through phenomenological relaxation rates under low doping regime with dominant intraband scattering. Such novel optical responses are vanished at high temperatures or overdoping conditions due to strong Drude behaviour. With the aid of approximations around Dirac points we have developed analytical formalism for many body interactions and is in good agreement with the Kubo approaches.


Probing the fractional quantum Hall phases in valley-layer locked bilayer MoS$_{2}$. (arXiv:2308.02821v2 [cond-mat.mes-hall] UPDATED)
Siwen Zhao, Jinqiang Huang, Valentin Crépel, Xingguang Wu, Tongyao Zhang, Hanwen Wang, Xiangyan Han, Zhengyu Li, Chuanying Xi, Senyang Pan, Zhaosheng Wang, Kenji Watanabe, Takashi Taniguchi, Benjamin Sacépé, Jing Zhang, Ning Wang, Jianming Lu, Nicolas Regnault, Zheng Vitto Han

Semiconducting transition-metal dichalcogenides (TMDs) exhibit high mobility, strong spin-orbit coupling, and large effective masses, which simultaneously leads to a rich wealth of Landau quantizations and inherently strong electronic interactions. However, in spite of their extensively explored Landau levels (LL) structure, probing electron correlations in the fractionally filled LL regime has not been possible due to the difficulty of reaching the quantum limit. Here, we report evidence for fractional quantum Hall (FQH) states at filling fractions 4/5 and 2/5 in the lowest LL of bilayer MoS$_{2}$, manifested in fractionally quantized transverse conductance plateaus accompanied by longitudinal resistance minima. We further show that the observed FQH states sensitively depend on the dielectric and gate screening of the Coulomb interactions. Our findings establish a new FQH experimental platform which are a scarce resource: an intrinsic semiconducting high mobility electron gas, whose electronic interactions in the FQH regime are in principle tunable by Coulomb-screening engineering, and as such, could be the missing link between atomically thin graphene and semiconducting quantum wells.


Non-Abelian Fibonacci quantum Hall states in 4-layer rhombohedral stacked graphene. (arXiv:2308.09702v2 [cond-mat.mes-hall] UPDATED)
Abigail Timmel, Xiao-Gang Wen

It is known that $n$-degenerate Landau levels with the same spin-valley quantum number can be realized by $n$-layer graphene with rhombohedral stacking under magnetic field $B$. We find that the wave functions of degenerate Landau levels are concentrated at the surface layers of the multi-layer graphene if the dimensionless ratio $\eta = \gamma_1/(v_F\sqrt{2e\hbar B/c}) \approx 9/\sqrt{B[\text{Tesla}]} \gg 1$, where $\gamma_1$ is the interlayer hopping energy and $v_F$ the Fermi velocity of single-layer graphene. This allows us to suggest that: 1) filling fraction $\nu=\frac12$ (or $\nu_n = 5\frac12$) non-Abelian state with Ising anyon can be realized in three-layer graphene for magnetic field $ B \in [ 2 , 9] $ Tesla; 2) filling fraction $\nu=\frac23$ (or $\nu_n = 7\frac13$) non-Abelian state with Fibonacci anyon can be realized in four-layer graphene for magnetic field $ B \in [ 5 , 9] $ Tesla. Here, $\nu$ is the total filling fraction in the degenerate Landau levels, and $\nu_n$ is the filling fraction measured from charge neutrality point which determines the measured Hall conductance. We have assumed the following conditions to obtain the above results: the exchange effect of Coulomb interaction polarizes the $SU(4)$ spin-valley quantum number in the degenerate Landau levels and effective dielectric constant $\epsilon \gtrsim 10$ to reduce the Coulomb interaction. The high density of states of multi-layer graphene helps to reduce the Coulomb interaction via screening.


Vortex structure and spectrum of atomic Fermi superfluid in a spherical bubble trap. (arXiv:2308.10065v2 [cond-mat.quant-gas] UPDATED)
Yan He, Chih-Chun Chien

The structures of multiply quantized vortices (MQVs) of an equal-population atomic Fermi superfluid in a rotating spherical bubble trap approximated as a thin shell are analyzed by solving the Bogoliubov-de Gennes (BdG) equation throughout the BCS-Bose Einstein condensation (BEC) crossover. Consistent with the Poincare-Hopf theorem, a pair of vortices emerge at the poles of the rotation axis in the presence of azimuthal symmetry, and the compact geometry provides confinement for the MQVs. While the single-vorticity vortex structure is similar to that in a planar geometry, higher-vorticity vortices exhibit interesting phenomena at the vortex center, such as a density peak due to accumulation of a normal Fermi gas and reversed circulation of current due to in-gap states carrying angular momentum, in the BCS regime but not the BEC regime because of the subtle relations between the order parameter and density. The energy spectrum shows the number of the in-gap state branches corresponds to the vorticity of a vortex, and an explanation based on a topological correspondence is provided.


Direct measurement of photoinduced transient conducting state in multilayer 2H-MoTe2. (arXiv:2308.16840v2 [cond-mat.mes-hall] UPDATED)
XinYu Zhou, H Wang, Q M Liu, S J Zhang, S X Xu, Q Wu, R S Li, L Yue, T C Hu, J Y Yuan, S S Han, T Dong, D Wu, N L Wang

Ultrafast light-matter interaction has emerged as a powerful tool to control and probe the macroscopic properties of functional materials, especially two-dimensional transition metal dichalcogenides which can form different structural phases with distinct physical properties. However, it is often difficult to accurately determine the transient optical constants. In this work, we developed a near-infrared pump - terahertz to midinfrared (12-22 THz) probe system in transmission geometry to measure the transient optical conductivity in 2H-MoTe2 layered material. By performing separate measurements on bulk and thin-film samples, we are able to overcome issues related to nonuniform substrate thickness and penetration depth mismatch and to extract the transient optical constants reliably. Our results show that photoexcitation at 690 nm induces a transient insulator-metal transition, while photoexcitation at 2 um has a much smaller effect due to the photon energy being smaller than the band gap of the material. Combining this with a single-color pump-probe measurement, we show that the transient response evolves towards 1T' phase at higher flunece. Our work provides a comprehensive understanding of the photoinduced phase transition in the 2H-MoTe2 system.


Fractional quantum Hall states with variational Projected Entangled-Pair States: a study of the bosonic Harper-Hofstadter model. (arXiv:2309.12811v2 [cond-mat.str-el] UPDATED)
Erik Lennart Weerda, Matteo Rizzi

An important class of model Hamiltonians for investigation of topological phases of matter consists of mobile, interacting particles on a lattice subject to a semi-classical gauge field, as exemplified by the bosonic Harper-Hofstadter model. A unique method for investigations of two-dimensional quantum systems are the infinite projected-entangled pair states (iPEPS), as they avoid spurious finite size effects that can alter the phase structure. However, due to no-go theorems in related cases this was often conjectured to be impossible in the past. In this letter, we show that upon variational optimization the infinite projected-entangled pair states can be used to this end, by identifying fractional Hall states in the bosonic Harper-Hofstadter model. The obtained states are characterized by showing exponential decay of bulk correlations, as dictated by a bulk gap, as well as chiral edge modes via the entanglement spectrum.


Found 8 papers in prb
Date of feed: Tue, 10 Oct 2023 03:17:01 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)

Deformation response of highly stretchable and ductile graphene kirigami under uniaxial and biaxial tension
Pan Shi, Yao Chen, Ye Wei, Jian Feng, Tong Guo, Yongming Tu, and Pooya Sareh
Author(s): Pan Shi, Yao Chen, Ye Wei, Jian Feng, Tong Guo, Yongming Tu, and Pooya Sareh

Kirigami, the ancient technique of paper cutting, has been successfully applied to enhance the stretchability and ductility of nanoscale graphene. However, existing experimentally realized graphene kirigami (GK) are created by introducing parallel cuts, exhibiting exceptional mechanical properties i…


[Phys. Rev. B 108, 134105] Published Mon Oct 09, 2023

High-temperature vacancy-induced magnetism in nanostructured materials
D. H. Mosca, J. Varalda, and C. A. Dartora
Author(s): D. H. Mosca, J. Varalda, and C. A. Dartora

Recently, vacancy-induced ferromagnetism in nanostructured materials, that in the pristine state are diamagnetic, aroused great interest among researchers due to their strong potential for the development of new technologies. In particular, vacancy-induced ferromagnetism is persistent at high temper…


[Phys. Rev. B 108, 134410] Published Mon Oct 09, 2023

Schwinger boson study of the ${J}_{1}\text{−}{J}_{2}\text{−}{J}_{3}$ kagome Heisenberg antiferromagnet with Dzyaloshinskii-Moriya interactions
Dario Rossi, Johannes Motruk, Louk Rademaker, and Dmitry A. Abanin
Author(s): Dario Rossi, Johannes Motruk, Louk Rademaker, and Dmitry A. Abanin

Schwinger boson mean-field theory is a powerful approach to study frustrated magnetic systems, which allows to distinguish long-range magnetic orders from quantum spin liquid phases, where quantum fluctuations remain strong up to zero temperature. In this paper, we use this framework to study the He…


[Phys. Rev. B 108, 144406] Published Mon Oct 09, 2023

Interaction-induced Liouvillian skin effect in a fermionic chain with a two-body loss
Shu Hamanaka, Kazuki Yamamoto, and Tsuneya Yoshida
Author(s): Shu Hamanaka, Kazuki Yamamoto, and Tsuneya Yoshida

Despite recent intensive research on topological aspects of open quantum systems, effects of strong interactions have not been sufficiently explored. In this paper, we demonstrate that complex-valued interactions induce the Liouvillian skin effect by analyzing a one-dimensional correlated model with…


[Phys. Rev. B 108, 155114] Published Mon Oct 09, 2023

Persistent current-carrying state of charge quasiparticles in an $np$ ribbon featuring a single Dirac cone
Anatoly M. Kadigrobov and Ilya M. Eremin
Author(s): Anatoly M. Kadigrobov and Ilya M. Eremin

The formation of persistent charge currents in mesoscopic systems remains an interesting and actual topic of condensed matter research. Here, we analyze the formation of spontaneous arising persistent currents of charged fermions in two-dimensional electron-hole ribbons on the top and bottom of a th…


[Phys. Rev. B 108, 155407] Published Mon Oct 09, 2023

Opacity of graphene independent of light frequency and polarization due to the topological charge of the Dirac points
Matheus S. M. de Sousa and Wei Chen
Author(s): Matheus S. M. de Sousa and Wei Chen

The opacity of graphene is known to be approximately given by the fine-structure constant $α$ times $π$. We point out the fact that the opacity is roughly independent of the frequency and polarization of the light can be attributed to the topological charge of the Dirac points. As a result, one can …


[Phys. Rev. B 108, 165201] Published Mon Oct 09, 2023

Symmetry breaking induced insulating electronic state in ${\mathrm{Pb}}_{9}\mathrm{Cu}{({\mathrm{PO}}_{4})}_{6}\mathrm{O}$
Jiaxi Liu, Tianye Yu, Jiangxu Li, Jiantao Wang, Junwen Lai, Yan Sun, Xing-Qiu Chen, and Peitao Liu
Author(s): Jiaxi Liu, Tianye Yu, Jiangxu Li, Jiantao Wang, Junwen Lai, Yan Sun, Xing-Qiu Chen, and Peitao Liu

The recent experimental claim of room-temperature ambient-pressure superconductivity in a Cu-doped lead- apatite (LK-99) has ignited substantial research interest in both experimental and theoretical domains. Previous density functional theory (DFT) calculations with the inclusion of an on-site Hubb…


[Phys. Rev. B 108, L161101] Published Mon Oct 09, 2023

Long-range, short-wavelength, and ultrafast heat conduction driven by three plasmon modes supported by graphene
Jose Ordonez-Miranda, Yuriy A. Kosevich, Masahiro Nomura, and Sebastian Volz
Author(s): Jose Ordonez-Miranda, Yuriy A. Kosevich, Masahiro Nomura, and Sebastian Volz

We demonstrate the existence and propagation of three hybrid modes of surface plasmon polaritons supported by two graphene monolayers coating a solid film. These modes propagate long distances with short wavelengths, which are suitable features to enhance the heat conduction along the film interface…


[Phys. Rev. B 108, L161404] Published Mon Oct 09, 2023

Found 1 papers in prl
Date of feed: Tue, 10 Oct 2023 03:16:59 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)

Mechanistic Insights into Water Autoionization through Metadynamics Simulation Enhanced by Machine Learning
Ling Liu, Yingqi Tian, Xuanye Yang, and Chungen Liu
Author(s): Ling Liu, Yingqi Tian, Xuanye Yang, and Chungen Liu

Machine learning-assisted metadynamics is used to study water autoionization, one of the most important properties of water for all biological and chemical process including electrolysis (related to batteries).


[Phys. Rev. Lett. 131, 158001] Published Mon Oct 09, 2023

Found 2 papers in pr_res
Date of feed: Tue, 10 Oct 2023 03:17:01 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)

Spectroscopic evidence for engineered hadronic bound state formation in repulsive fermionic $\text{SU}(N)$ Hubbard systems
Miklós Antal Werner, Cătălin Paşcu Moca, Márton Kormos, Örs Legeza, Balázs Dóra, and Gergely Zaránd
Author(s): Miklós Antal Werner, Cătălin Paşcu Moca, Márton Kormos, Örs Legeza, Balázs Dóra, and Gergely Zaránd

Particle formation represents a central theme in various branches of physics, often associated to confinement. Here we show that dynamical hadron formation can be spectroscopically detected in an ultracold atomic setting within the most paradigmatic and simplest model of condensed matter physics, th…


[Phys. Rev. Research 5, 043020] Published Mon Oct 09, 2023

Supercurrent interference in HgTe-wire Josephson junctions
Wolfgang Himmler, Ralf Fischer, Michael Barth, Jacob Fuchs, Dmitriy A. Kozlov, Nikolay N. Mikhailov, Sergey A. Dvoretsky, Christoph Strunk, Cosimo Gorini, Klaus Richter, and Dieter Weiss
Author(s): Wolfgang Himmler, Ralf Fischer, Michael Barth, Jacob Fuchs, Dmitriy A. Kozlov, Nikolay N. Mikhailov, Sergey A. Dvoretsky, Christoph Strunk, Cosimo Gorini, Klaus Richter, and Dieter Weiss

Wires made of topological insulators (TI) are a promising platform for searching for Majorana bound states. These states can be probed by analyzing the fractional ac Josephson effect in Josephson junctions with the TI wire as a weak link. An axial magnetic field can be used to tune the system from t…


[Phys. Rev. Research 5, 043021] Published Mon Oct 09, 2023

Found 2 papers in nano-lett
Date of feed: Mon, 09 Oct 2023 13:11:50 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)

[ASAP] Symmetry Engineering in Twisted Bilayer WTe2
Yijin Zhang, Keisuke Kamiya, Takato Yamamoto, Masato Sakano, Xiaohan Yang, Satoru Masubuchi, Shota Okazaki, Keisuke Shinokita, Tongmin Chen, Kohei Aso, Yukiko Yamada-Takamura, Yoshifumi Oshima, Kenji Watanabe, Takashi Taniguchi, Kazunari Matsuda, Takao Sasagawa, Kyoko Ishizaka, and Tomoki Machida

TOC Graphic

Nano Letters
DOI: 10.1021/acs.nanolett.3c02327

[ASAP] Submillimeter-Long WS2 Nanotubes: The Pathway to Inorganic Buckypaper
Vojtěch Kundrát, Rita Rosentsveig, Kristýna Bukvišová, Daniel Citterberg, Miroslav Kolíbal, Shachar Keren, Iddo Pinkas, Omer Yaffe, Alla Zak, and Reshef Tenne

TOC Graphic

Nano Letters
DOI: 10.1021/acs.nanolett.3c02783

Found 3 papers in nat-comm


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)

Porphene and porphite as porphyrin analogs of graphene and graphite
< author missing >

Electronic Janus lattice and kagome-like bands in coloring-triangular MoTe2 monolayers
< author missing >

Electrostatic force promoted intermolecular stacking of polymer donors toward 19.4% efficiency binary organic solar cells
< author missing >