arXiv subjects

Qizhong Zhu

Publications and source records attributed to Qizhong Zhu.

At least 19 recordsLinked to original sources

arXiv2026

Interaction-induced moiré lattices: from mosaic mobility edges to many-body localization

We study localization driven solely by interparticle interactions in moiré lattice systems without intrinsic disorder or externally imposed quasiperiodic potentials. We consider a one-dimensional bilayer with incommensurate lattice constants, described by a spin-dependent Fermi-Hubbard-type model with short-range interlayer interactions, where quasiperiodicity emerges only through interactions. Exact diagonalization shows that quenching hopping in one layer generates an interaction-induced mosaic potential with multiple mobility edges. When both layers are dynamical, increasing interlayer interactions drives transitions among ergodic, critical, and many-body localized regimes, with energy-dependent coexistence in certain parameter ranges. An exact mapping to a noninteracting single-particle model on a higher-dimensional structured graph provides a unified interpretation of these results and suggests an experimentally accessible route to interaction-induced moiré physics and localization.

cond-mat.dis-nn↗

arXiv2025

Interaction-induced reentrance of Bose glass and quench dynamics of Bose gases in twisted bilayer and quasicrystal optical lattices

We investigate the ground-state and dynamical properties of ultracold Bose gases in optical lattices with a quasicrystal structure, inspired by recent experiments on twisted bilayer and quasicrystalline optical lattices. The interplay between on-site repulsive interactions and the quasiperiodic potential leads to rich physics. At low filling factors, increasing the interaction strength induces a delocalization effect that transforms a Bose-glass (BG) phase-characterized by disconnected superfluid (SF) regions-into a robust SF phase with a percolated network of SF clusters. This transition is quantitatively identified via the percolation probability. At higher filling factors, we uncover a reentrant behavior: with increasing interaction, the system first changes from BG to SF, but further strengthening reverses the trend, restoring the BG phase. This reentrance originates from an interaction-driven rearrangement of particles, where a percolated SF network fragments into isolated SF islands as repulsion dominates. The quench dynamics show distinct transient features: intraphase quenches cause minor variations in the percolation probability and the inverse participation ratio (IPR), while interphase quenches produce strong responses. In particular, an SF-to-BG quench exhibits an abrupt loss of global SF connectivity, whereas a BG-to-SF quench shows oscillatory percolation and a gradual IPR decrease, stabilizing the SF phase. These results elucidate the competition between quasiperiodicity and interactions in ultracold Bose gases and offer insights relevant to current experiments with twisted bilayer and quasicrystal optical lattices.

cond-mat.quant-gas↗

arXiv2025

Phonon-scattering-induced quantum linear magnetoresistance up to room temperature

The realization of quantum transport effects at elevated temperatures has long intrigued researchers due to the implications for unveiling novel physics and developing quantum devices. In this work, we report remarkable quantum linear magnetoresistance (LMR) in the Weyl semiconductor tellurium at high temperatures of 40-300 K under strong magnetic fields up to 60 T. At high fields, the Weyl band features a large energy gap between the lowest and first Landau levels, which suppresses thermal excitation and preserves Landau quantization at high temperatures. The LMR is observed as long as majority carriers remain in the lowest Landau level without requiring monochromaticity, allowing it to persist up to room temperature. The inverse relationship between the LMR slope and temperature provides clear evidence that quantum LMR originates from high-temperature phonon scattering in the quantum limit, firstly demonstrating a theoretical prediction made nearly fifty years ago. This study highlights the key role of electron-phonon interaction and reveals an innovative quantum mechanism for achieving high-temperature LMR, fundamentally distinct from previous findings. Our results bridge a gap in the understanding of phonon-mediated quantum-limit physics and establish strong magnetic fields at high temperatures as a promising platform for exploring novel quantum phenomena.

cond-mat.mes-hall↗

arXiv2025

$\mathbb{Z}_2$ topological trion insulator

Trions, charged quasiparticles formed by binding an exciton to an excess charge carrier, dominate the optical response of doped transition metal dichalcogenides (TMDs), and the study of the transport properties of trions in TMDs may have application in developing high-speed excitonic and optoelectronic devices. However, an important building block for low-dissipation optoelectronic devices that provides dissipationless transport channels for trions has remained elusive. Here, we propose the concept of a $\mathbb{Z}_2$ topological trion insulator that features helical dissipationless edge states for trions. This is realized for intralayer trions, which inherit the valley-orbit coupling of intralayer excitons in TMDs subject to a moiré periodic potential. We find that under certain circumstances, the moiré trion band becomes topological, characterized by the $\mathbb{Z}_2$ topological number. We further provide two specific material realizations of this $\mathbb{Z}_2$ topological insulator: a doped monolayer TMD placed on top of a twisted hBN substrate, and a generic twisted TMD heterobilayer. We also examine the effect of charge screening and find that the $\mathbb{Z}_2$ topological trion insulator remains robust. Our work paves the way toward realizing dissipationless excitonic devices.

cond-mat.mes-hall↗

arXiv2025

Interaction induced moiré systems in twisted bilayer optical lattices

Moiré related physics in twisted bilayer two-dimensional (2D) materials has attracted widespread interest in condensed matter physics. Simulation of moiré related physics in cold atom platform is expected to outperform the 2D materials thanks to its advantage of higher tunablility. Here, we demonstrate that, the cold atom platform enables a new mechanism of moiré lattice formation, induced by interlayer interaction with intrinsic "dynamical" character, in contrast to conventional moiré lattice induced by "static" ways such as single-particle interlayer tunneling. Specifically, we consider a twisted bilayer Bose-Hubbard model with vanishing interlayer tunneling, and the bilayer is solely coupled through interlayer interaction that originates from contact interaction of atoms. We find that this system hosts a plethora of novel phases unique to this dynamical lattice, including a variety of Mott insulator (MI) and superfluid (SF) phases either preserving or breaking moiré lattice symmetry, phases with one layer in SF and the other in MI, "interlocked" MI, and self-localized phases at commensurate twist angles, which exhibits the characteristics of Bose glass and quasi-many-body localization in the absence of (quasi)disorder or quasicrystalline lattices. Our prediction can be readily observed in current experimental setup of twisted bilayer optical lattices, opening up new avenues for exploring the rich physics of interaction induced moiré systems in cold atoms.

cond-mat.quant-gas↗

arXiv2025

Topological exciton bands and many-body exciton phases in transition metal dichalcogenide trilayer heterostructures

Twisted multilayer transition metal dichalcogenides (TMDs) are a promising platform for realizing topological exciton phases. Here we propose that twisted TMD heterotrilayers WX$_2$/MX$_2$/WX$_2$ with layer symmetry represents a realistic system for realizing topological exciton bands and interesting many-body excitonic phases, simply by tuning the twist angle. These symmetric heterotrilayers form a type-II band alignment, where the electrons are confined in the middle layer and holes are distributed among the outer two layers, for the lowest energy excitons. The outer two layers are then rotated at different centers by opposite angles, forming a helical structure. Interlayer excitons with opposite dipoles are hybridized by the coupling between outer two layers, resulting in topological moiré exciton bands. Furthermore, by constructing a three-orbital tight-binding model, we map the many-body phase diagram of interacting dipolar and quadrupolar excitons at different twist angles and exciton densities and reveal the existence of sublattice-dependent staggered superfluid and Mott insulator phases. The recent experimental observation of quadrupolar excitons in symmetric heterotrilayers brings the intriguing phases predicted in this study within immediate experimental reach.

cond-mat.mes-hall↗

arXiv2025

Induced Interactions and Bipolarons in Spin-Orbit Coupled Bose-Einstein Condensates

Impurities immersed in a Bose-Einstein condensate (BEC) can interact indirectly through the exchange of Bogoliubov excitations. These impurities, which form dressed quasiparticles known as Bose polarons due to their interaction with the BEC, can pair up to form a bound state called bipolarons, via an induced interaction. Previous studies on induced interactions have primarily focused on cases with an isotropic excitation spectrum. In this work, we investigate the properties of induced interactions and bipolarons mediated by anisotropic Bogoliubov excitations using field theory. Taking a BEC with spin-orbit coupling as an example, we show that the induced interaction becomes anisotropic. Notably, a double-minima feature appears in the induced interaction in momentum space due to the exchange of roton excitations. Additionally, we calculate the binding energy and wave functions of these bipolarons induced by anisotropic interactions. Unlike previously studied bipolarons formed through the exchange of isotropic phonon excitations, we identify a new type of bipolarons whose wave functions feature a double-peak structure under strong impurity-boson interactions. Our work extends the theory of induced interactions from isotropic to anisotropic systems, and reveals the novel features in both the induced interactions and bipolarons arising from BEC with an unconventional excitation spectrum.

cond-mat.quant-gas↗

arXiv2024

Ground State Phases and Topological Excitations of Spin-1 Bose-Einstein Condensate in Twisted Optical Lattices

Recently, the simulation of moiré physics using cold atom platforms has gained significant attention. These platforms provide an opportunity to explore novel aspects of moiré physics that go beyond the limits of traditional condensed matter systems. Building on recent experimental advancements in creating twisted bilayer spin-dependent optical lattices for pseudospin-1/2 Bose gases, we extend this concept to a trilayer optical lattice for spin-1 Bose gases. Unlike conventional moiré patterns, which are typically induced by interlayer tunneling or interspin coupling, the moiré pattern in this trilayer system arises from inter-species atomic interactions. We investigate the ground state of Bose-Einstein condensates loaded in this spin-1 twisted optical lattice under both ferromagnetic and antiferromagnetic interactions. We find that the ground state forms a periodic pattern of distinct phases in the homogeneous case, including ferromagnetic, antiferromagnetic, polar, and broken axial symmetry phases. Additionally, by quenching the optical lattice potential strength, we examine the quench dynamics of the system above the ground state and observe the emergence of topological excitations such as vortex pairs. This study provides a pathway for exploring the rich physics of spin-1 twisted optical lattices and expands our understanding of moiré systems in synthetic quantum platforms.

cond-mat.quant-gas↗

arXiv2024

Supercurrent-carrying supersolid in spin-orbit-coupled Bose-Einstein condensates

One of brilliant achievements in spin-orbit-coupled Bose-Einstein condensates is the discovery and observation of the supersolid stripe states. So far, all studied supersolid stripe states do not carry supercurrent. In this work, we reveal the existence of supercurrent-carrying supersolids in spin-orbit-coupled Bose-Einstein condensates. The supersolid family has a parabolic-like dispersion relation and carries supercurrent which is proportional to the quasimomentum. Energetic and dynamical instabilities can break supercurrent-carrying ability of this supersolid family. An insightful interpretation of the dynamical instability of supercurrent-carrying supersolids from the pure plane-wave phase is provided.

cond-mat.quant-gas↗

arXiv2023

Searching for Unconventional Superfluid in Excitons of Monolayer Semiconductors

It is well known that two-dimensional (2D) bosons in homogeneous space cannot undergo real Bose-Einstein condensation, and the superfluid to normal phase transition is Berezinskii-Kosterlitz-Thouless (BKT) type, associated with vortex-antivortex pair unbinding. Here we point out a 2D bosonic system whose low energy physics goes beyond conventional paradigm of 2D {\it homogeneous} bosons, i.e., intralayer excitons in monolayer transition metal dichalcogenides. With intrinsic valley-orbit coupling and valley Zeeman energy, exciton dispersion becomes linear at small momentum, giving rise to a series of novel features. The critical temperature of Bose-Einstein condensation of these excitons is nonzero, suggesting true long-range order in 2D homogeneous system. The dispersion of Goldstone mode at long wavelength has the form $\varepsilon(\boldsymbol{q})\sim\sqrt{q}$, in contrast to conventional linear phonon spectrum. The vortex energy deviates from the usual logarithmic form with respect to system size, but instead has an additional linear term. Superfluid to normal phase transition is no longer BKT type for system size beyond a characteristic scale, without discontinuous jump in superfluid density. With the recent experimental progress on exciton fluid at thermal equilibrium in monolayer semiconductors, our work points out an experimentally accessible system to search for unconventional 2D superfluids beyond BKT paradigm.

cond-mat.quant-gas↗

arXiv2023

$\mathbb{Z}_n$ symmetry broken supersolid in spin-orbit-coupled Bose-Einstein condensates

Supersolid is an exotic state of matter characterized by both superfluid properties and periodic particle density modulation, due to spontaneous breaking of U(1) gauge symmetry and spatial translation symmetry, respectively. For conventional supersolids,continuous translation symmetry breaking is accompanied by one gapless Goldstone mode in the excitation spectra. An interesting question naturally arises: what is the consequence of breaking discrete translation symmetry for supersolids? In this work, we propose the concept of $\mathbb{Z}_n$ supersolid resulting from spontaneous breaking of a discrete $\mathbb{Z}_n$ symmetry, or equivalently, a discrete translation symmetry. This $\mathbb{Z}_n$ supersolid is realized in the stripe phase of spin-orbit-coupled Bose-Einstein condensate under an external periodic potential with period $1/n$ of intrinsic stripe period. For $n\geq2$, there are $n$ degenerate ground states with spontaneously broken lattice translation symmetry. The low-energy excitations of $\mathbb{Z}_n$ supersolid include a pseudo-Goldstone mode, whose excitation gap at long wavelength limit is found to decrease fast with $n$. We further numerically show that, when confined in a harmonic trap, a spin-dependent perturbation can result in the transition between degenerate ground states of $\mathbb{Z}_n$ supersolid. With the integer $n$ tunable using the experimental technique of generating subwavelength optical lattice, the $\mathbb{Z}_n$ supersolid proposed here offers a cold atom platform to simulate physics related with generic $\mathbb{Z}_n$ symmetry breaking, which is interesting not only in the field of cold atoms, but also in particle physics and cosmology.

cond-mat.quant-gas↗

arXiv2023

Dynamical properties of quasiparticles in a tunable Kekulé graphene superlattice

We investigate the dynamical properties of quasiparticles in graphene superlattices with three typical Kekulé distortions (i.e., Kekulé-O, Kekulé-Y and Kekulé-M). On the one hand, we numerically show the visualized evolution process of Kekulé quasiparticles; while on the other hand, we analytically obtain the centroid trajectory of the quasiparticles, and both of them agree well with each other. The results reveal that the relativistic Zitterbewegung (ZB) phenomenon occurs in the Kekulé systems. Furthermore, through analyzing the frequency of ZB, we unveil the one-to-one relationship between ZB and Kekulé textures, i.e., the ZB frequenies of Kekulé-O, Kekulé-Y and Kekulé-M quasiparticles feature single, double and six frequencies, respectively. Finally, we propose a scheme to distinguish among different Kekulé textures from the dynamical perspective. The predictions in this paper are expected to be experimentally verified in the near future, so as to facilitate further research of Kekulé structures in solid materials or artificial systems.

cond-mat.mes-hall↗

arXiv2023

Single photon emitters with polarization and orbital angular momentum locking in monolayer semiconductors

Excitons in monolayer transition metal dichalcogenide are endowed with intrinsic valley-orbit coupling between their center-of-mass motion and valley pseudospin. When trapped in a confinement potential, e.g., generated by strain field, we find that intralayer excitons are valley and orbital angular momentum (OAM) entangled. By tuning trap profile and external magnetic field, one can engineer the exciton states at ground state, and realize a series of valley-OAM entangled states. We further show that the OAM of excitons can be transferred to emitted photons, and these novel exciton states can naturally serve as polarization-OAM locked single photon emitters, which under certain circumstance become polarization-OAM entangled, highly tunable by strain trap and magnetic field. Our proposal demonstrates a novel scheme to generate polarization-OAM locked/entangled photons at nanoscale with high degree of integrability and tunability, pointing to exciting opportunities for quantum information applications.

cond-mat.mes-hall↗

arXiv2023

Metastable supersolid in spin-orbit coupled Bose-Einstein condensates

Supersolid is a special state of matter with both superfluid properties and spontaneous modulation of particle density. In this paper, we focus on the supersolid stripe phase realized in a spin-orbit coupled Bose-Einstein condensate and explore the properties of a class of metastable supersolids. In particular, we study a one-dimensional supersolid whose characteristic wave number $k$ (magnitude of wave vector) deviates from $k_{m}$, i.e., the one at ground state. In other words, the period of density modulation is shorter or longer than the one at ground state. We find that this class of supersolids can still be stable if their wave numbers fall in the range $k_{c1}<k<k_{c2}$, with two thresholds $k_{c1}$ and $k_{c2}$. Stripes with $k$ outside this range suffer from dynamical instability with complex Bogoliubov excitation spectrum at long wavelength. Experimentally, these stripes with $k$ away from $k_m$ are accessible by exciting the longitudinal spin dipole mode, resulting in temporal oscillation of stripe period as well as $k$. Within the mean-field Gross-Pitaevskii theory, we numerically confirm that for a large enough amplitude of spin dipole oscillation, the stripe states become unstable through breaking periodicity, in qualitative agreement with the existence of thresholds of $k$ for stable stripes. Our work extends the concept of supersolid and uncovers a new class of metastable supersolids to explore.

cond-mat.quant-gas↗

arXiv2022

Moiré exciton condensate: nonlinear Dirac point, broken-symmetry Bloch waves and unusual optical selection rules

Moiré exciton features tunable Dirac dispersion and spatially dependent optical selection rules. With the long lifetime due to its interlayer nature, it is promising to realize a Bose-Einstein condensation of moiré excitons. Here we study the properties of moiré exciton condensate within the mean-field theory, with special focus on exciton-exciton interaction effect on the nonlinear Bloch band and Bloch waves of exciton condensate in moiré potential. We find the nonlinear dispersion of the moiré exciton condensate exhibits complex loop structure induced by exciton-exciton interaction. A nonlinear Dirac cone emerges at $\boldsymbolΓ$ point of the Bloch band, with a three-fold degenerate nonlinear Dirac point. Each degenerate Bloch wave at nonlinear Dirac point spontaneously breaks $C3$ rotational symmetry of the moiré potential, and themselves differ by $C3$ rotations. Since they reside in the light cone, these nontrivial Bloch band structure and broken-symmetry Bloch waves can be experimentally detected by examining light emission from those states. Symmetry breaking of Bloch states implies unusual optical selection rules compared with single exciton case: moiré exciton condensate at $\boldsymbolΓ$ point emits light with all three components of polarization instead of only left or right circular polarization. We further propose that, by applying in-plane electric field on one layer to drive an initially optically dark exciton condensate towards light cone, the light polarization of final states as well as their dependence on field direction serves as the smoking gun for experimental observation.

cond-mat.mes-hall↗

arXiv2022

Electron-Electron Interaction and Weak Antilocalization Effect in a Transition Metal Dichalcogenide Superconductor

In disordered transition-metal dichalcogenide (TMD) superconductor, both the strong spin-orbit coupling (SOC) and disorder show remarkable effects on superconductivity. However, the features of SOC and disorder were rarely detected directly. Here we report the quantum transport behaviors arising from the interplay of SOC and disorder in the TMD superconductor 1T-NbSeTe. Before entering the superconducting state, the single crystal at low temperature shows a resistivity upturn, which is T1/2 dependent and insensitive to the applied magnetic fields. The magnetoresistance (MR) at low temperatures shows a H1/2 dependence at high magnetic fields. The characteristics are in good agreement with the electron-electron interaction (EEI) in a disordered conductor. In addition, the upturn changes and MR at low magnetic fields suggest the contribution of weak antilocalization (WAL) effect arising from the strong SOC in the material. Moreover, the quantitative analyses of the transport features in different samples imply anomalous disorder-enhanced superconductivity that needs to be further understood. The results reveal the disorder enhanced EEI and the strong SOC induced WAL effect in 1T-NbSeTe, which illustrate the resistivity minimum in the widely studied doped superconductors. The work also provides insights into the disorder effect on the superconductivity.

cond-mat.supr-con↗

arXiv2021

Chaotic dynamics of Bose-Einstein condensate in a density-dependent gauge field

In this work we study the effect of density-dependent gauge field on the collective dynamics of a harmonically trapped Bose-Einstein condensate, beyond the linear response regime. The densitydependent gauge field, as a backaction of the condensate, can in turn affect the condensate dynamics, resulting in highly nonlinear equations of motion. We find that the dipole and breathing oscillations of the condensate along the direction of gauge field are coupled by this field. For a quasi-onedimensional condensate, this coupling makes the collective motion quasiperiodic. While for a quasitwo-dimensional condensate, the gauge field can also induce a Hall effect, manifested as an additional coupling between dipole and breathing oscillations in perpendicular direction. When the densitydependent gauge field is strong, the interplay between these oscillations can cause the collective dynamics of the condensate to become chaotic. Our findings reveal an important effect of dynamical gauge field on the nonlinear dynamics of a Bose-Einstein condensate.

cond-mat.quant-gas↗

arXiv2019

Coulomb effects on topological band inversion in the moiré of WSe$_2$/BAs heterobilayer

Quantum spin Hall (QSH) insulator with large gap is highly desirable for potential spintronics application. Here we realize electrically tunable QSH insulator with large gap in van der Waals heterobilayer of monolayer transition metal dichalcogenide (TMD) and hexagonal BAs. When the type II band alignment gets inverted in an electric field, the hybridization by interlayer hopping between the spin-valley locked valence band edges in TMD and the BAs conduction band edges leads to a stacking-configuration dependent topological band inversion. In the non-interacting limit, the double spin degeneracy of BAs leaves an un-hybridized conduction band inside the gap, so the heterobilayer is a spin-valley locked metal instead of a QSH insulator. With the Coulomb interaction accounted in the double-layer geometry, the interaction with the hybridization induced electric dipole shifts this un-hybridized conduction band upwards in energy, giving rise to a sizable global QSH gap. Consequently, this heterobilayer provides a platform for engineering electrically tunable QSH insulator with sizable band gap. In the long period moiré pattern with the spatial variation of local stacking-configurations, the competition between Coulomb interaction and interlayer hopping leads to superstructures of QSH insulators and excitonic insulators.

cond-mat.mes-hall↗