arXiv subjects

Quansheng Wu

Publications and source records attributed to Quansheng Wu.

At least 19 recordsLinked to original sources

arXiv2026

Gauge-covariant magnetic Bloch sums for general multiorbital Hofstadter models

We formulate a unified treatment of the Hofstadter problem for general two-dimensional multiorbital Peierls tight-binding Hamiltonians using a gauge-covariant magnetic Bloch-sum basis. The construction retains the full Bravais geometry, arbitrary intracell orbital positions, and the original hopping table, so lattice geometry, orbital embedding, hopping range, and orbital content can all be handled within the same framework. At rational flux $Φ/Φ_0=p/q$, commuting magnetic translations reduce the Peierls Hamiltonian to minimal $qN_{\rm orb}\times qN_{\rm orb}$ blocks. Their dimension depends only on the flux through the primitive cell, even when the fractional orbital coordinates are irrational. Electromagnetic gauge transformations act by unitary conjugation within the construction and do not alter the required magnetic supercell. We derive an explicit sparse matrix in an oblique Landau gauge and establish the associated band counting, spectral redundancy, Chern-number formulation, magnetic spatial constraints, and flux periodicity. Numerical examples include elementary lattices, topological and flat-band models, and a spinful 22-band Wannier Hamiltonian of monolayer $\mathrm{MoS}_2$, demonstrating a direct interface with first-principles electronic-structure calculations. As a complementary representation, we also derive exact generalized Harper equations from the same hopping data and relate them to the finite magnetic-Bloch blocks.

cond-mat.mes-hall↗

arXiv2026

A Catalogue of Topological Moiré Bands in Twisted Semiconductors

Twisted two-dimensional semiconductors provide a route to flat and topological moiré minibands, but systematic principles for organizing their material dependence have remained unclear. Here, we establish a high-throughput framework that integrates structural relaxation, first-principles electronic structure calculations, and moiré band topology. We apply this framework to 43 experimentally realized monolayers and 91 symmetry-inequivalent bilayer prototypes, yielding over 1,000 angle-resolved moiré electronic band structures. This database reveals that the low-energy moiré electronic structure is organized primarily by the valley character of the parent band edge together with stacking symmetry. In $Γ$-valley systems, the miniband width usually follows a nearly quadratic twist-angle scaling, consistent with a folding-dominated kinetic-energy scale. In $K$-valley systems, stacking-controlled interlayer hybridization governs whether parent Berry curvature is redistributed into isolated valley Chern minibands. By contrast, $M$-valley systems form a more material-specific class associated with anisotropic and symmetry-constrained band folding. The same valley-and-stacking hierarchy rationalizes the emergence or suppression of $\mathbb{Z}_2$ minibands, and surface termination in Janus bilayers provides a microscopic knob for changing the relevant valley character. These results establish a materials-level organizing principle for designing flat and topological moiré bands in twisted semiconductors.

cond-mat.mtrl-sci↗

arXiv2026

Relative hybridization textures as local coordinates for band geometry and topology

Global diagnostics such as Berry curvature and quantum metrics characterize the geometry and topology of an occupied Bloch subspace, leaving the microscopic sectors that carry this structure implicit. We introduce the relative hybridization coordinate $Z$ as a projector-level diagnostic connecting these global quantities to local degrees of freedom. As the Grassmann graph coordinate relative to a chosen sector, $Z$ reconstructs the local projector and retains the phase and matrix orientation absent from ordinary weight or fat-band descriptions. On valid chart patches, its momentum-space texture encodes Berry curvature, quantum metric, Berry phases, and Wilson loops, while chart obstructions appear as rank-drop defects whose balanced-chart winding of $\det Z$ gives the first Chern number. In the QWZ model this defect inventory reproduces the Chern phase diagram. In the lattice BHZ model, matrix $Z$ diagnoses the orbital $E|H$ partition as a robust matched chart for the QSH geometry, while the spin partition remains essential to the block and $\mathbb Z_2$ interpretation and shows rank deficiency as a matched chart in the spin-conserving limit. The relative hybridization coordinate thus provides a sector-resolved framework for relating band geometry and topology to microscopic structure.

cond-mat.mes-hall↗

arXiv2026

Entropy-Driven Structural Phase Transition in Nb$_3$Cl$_8$ via Density Functional Theory and an Effective Model

As a prototypical flat-band cluster Mott insulator on an effective triangular lattice, Nb$_3$Cl$_8$ is a potential candidate for hosting a quantum spin liquid (QSL) state. Nevertheless, a first-order structural phase transition around 90K transforms the high-temperature paramagnetic $α$ phase into the low-temperature nonmagnetic $β$ phase, suppressing the candidate QSL regime of the $α$ phase. To clarify the microscopic origin of this transition, we combine first-principles calculations with an extended Hubbard model to construct a unified free-energy framework. This framework reveals that the transition is jointly driven by phonon and spin entropy: the $α$ phase is stabilized by softer phonons and larger paramagnetic spin entropy, whereas the $β$ phase is favored by interlayer dimerization, which hardens the phonons and quenches the spin entropy through singlet formation. Furthermore, by evaluating the pressure-dependent generalized enthalpy, we provide a thermodynamic explanation for the suppression of the transition under c-axis uniaxial pressure, where stabilizing the $α$ phase may allow the candidate QSL regime of the $α$ phase to be explored at low temperatures.

cond-mat.mtrl-sci↗

arXiv2026

A Geometric Design Principle for $\mathbb{Z}_2$ Topological Phases in Twisted Triangular-Lattice Bilayers

Twisted van der Waals bilayers provide a versatile platform for moiré electronic states, yet a transferable symmetry-based principle for time-reversal-invariant $\mathbb{Z}_2$ moiré bands has remained largely missing. Here we show that triangular-lattice bilayers with symmetry-related stacking minima provide a geometric route to an emergent honeycomb moiré lattice. Band-edge states derived from the untwisted $Γ$ valley are trapped by the reconstructed stacking landscape, forming A/B moiré orbitals whose inter-domain coupling generates Dirac crossings. Spin--orbit coupling opens a topological gap, yielding an effective Kane--Mele description and a quantum spin Hall phase characterized by a nontrivial $\mathbb{Z}_2$ invariant. First-principles calculations for Janus BiTeBr confirm the robustness of this phase over a broad twist-angle range and demonstrate an electric-field-driven topological transition. Representative triangular-lattice bilayers further establish this symmetry-based design principle as a broadly applicable route to tunable moiré quantum spin Hall materials.

cond-mat.mtrl-sci↗

arXiv2026

Coexistence of topologically nontrivial and trivial insulating states in topological Anderson Chern insulator

The interplay between disorder and topology has become a central theme in condensed matter physics. Disorder can not only destroy topological phases but also induce them, as exemplified by the topological Anderson insulator (TAI). Here we show that, in close analogy, disorder can drive the clean-limit, time-reversal-broken(T-broken) quantum spin Hall state of ferromagnetic(FM) monolayer MnBi4Te7 into a quantum anomalous Hall phase, which was called topological Anderson Chern insulator (TACI). Using density functional theory (DFT) and nonequilibrium Green's func tion (NEGF) calculations in the presence of disorder, we identify disorder induced phases-including T-broken TAI, TACI, Normal insulator, etc., then construct a comprehensive phase diagram. To discriminate multiple phases in the strong disorder regime, we further use the density of states computed within the self-consistent Born approximation (SCBA), which in particular distinguishes gapped and ungapped topological phases. We find that the two effective band inversions of Hamiltonian are suppressed at distinct critical disorder strengths; the survival of a single inversion over a finite disorder window stabilizes the TACI. Remarkably, at strong disorder, we further propose a zero Hall plateau insulating state characterized by an insulating bulk and edge channels subject to diffusive scattering that can coexist with the TACI. This behavior is distinct from a conventional band-gap Chern insulator and provides a clear experimental signature.

cond-mat.dis-nn↗

arXiv2026

Percolation from Quantum Metric in Flat-Band Delocalization

The quantum metric is a fundamental ingredient of band quantum geometry and has recently at tracted intense interest, with most of its transport signatures appearing in the intrinsic second order nonlinear conductivity. In the clean limit, previous works argued that linear response conductivity is insensitive to the quantum metric, while the Berry curvature yields an intrinsic anomalous Hall con tribution. Here we combine analytic derivations with new numerics to show that disorder modifies the linear response conductivity dominated by geometric conductivity which is determined by the real space quantum metric. Focusing on a two dimensional multi-flatband stub-pyrochlore lattice, we identify a critical delocalized regime sandwiched between flat band localization and Anderson localization, characterized by finite geometric conductivity. Upon including spin orbit coupling, this regime evolves into a diffusive metallic phase, constituting a two dimensional inverse Anderson transition. Moreover, exploiting the connection between the real space quantum metric marker and the Wannier function spread, we construct a bond-percolation model on a square lattice. The resulting percolation region quantitatively coincides the critical delocalized regime, the exponent of which supports a classical percolation universality class. These findings suggest that flat band de localization can be understood as a classical percolation of quantum metric puddles. This advances our understanding of quantum geometric contributions to transport and establishes linear response measurements as a new avenue for accessing the quantum metric.

cond-mat.dis-nn↗

arXiv2026

Disentangling Anomalous Hall Effect Mechanisms and Extra Symmetry Protection in Altermagnetic Systems

We investigate the evolution of Anomalous Hall Conductivity (AHC) in a coplanar and collinear antiferromagnetic system with varying spin canting angles. A tight-binding model based on three t2g-orbitals in a body-centered tetragonal lattice is constructed, where the inclusion of third-nearest neighbor hopping is demonstrated to be essential for capturing the characteristic energy band splitting of altermagnetic materials. By employing a symmetry analysis based on spin space groups and treating spin-orbit coupling (SOC) as a perturbation, we theoretically distinguish and numerically verify two origins of the transverse transport: the conventional anomalous Hall effect (AHE) induced by net magnetization and the Crystal Hall Effect (CHE) arising from specific crystal symmetries. Our results show that the conductivity components driven by these two mechanisms follow distinct trigonometric dependencies on the canting angle. Crucially, we identify a hidden C110 rotational symmetry that has been previously overlooked in static magnetic group analyses. By expanding the AHC in terms of spin orientation vectors, we demonstrate that this symmetry acts as a bridge connecting distinct magnetic configurations with different canting angles, thereby strictly protecting the equivalence of orthogonal conductivity components in the collinear system.

cond-mat.mtrl-sci↗

arXiv2026

Symmetry-Indicated Time-Reversal-Doubled Axion Insulators

The axion insulator exhibits a topological magnetoelectric effect characterized by an axion angle $θ=π$, while the time-reversal-doubled axion insulator (T-DAXI) can be viewed as two copies of an axion insulator related by time-reversal symmetry. In this work, we show that a topological crystalline insulator with nonsymmorphic glide or screw symmetry hosts the T-DAXI phase. The spin-resolved topology of the T-DAXI phase is guaranteed by the nonsymmorphic symmetry invariant $δ_g=1$ or $δ_s=1$ in certain spin directions. In this phase, the partial axion angles are quantized to $π$, and the gapped surfaces realize half-quantized quantum spin Hall states. By applying an external magnetic field along the $z$ direction, electrons with opposite spins accumulate on opposite $(001)$ surfaces, producing a topological spin polarization in real space. When the magnetic field is time-periodic, this leads to an alternating spin current detectable in experiment. Using $\mathrm{\textit{ab initio}}$ calculations, we demonstrate that mixed bismuth monohalides Bi4Br3I and Bi4BrI3 realize the nonsymmorphic T-DAXI with $δ_g=δ_s=1$. Our findings not only reveal the symmetry-enforced T-DAXIs in nonsymmorphic topological crystalline insulators, but also introduce the spin magnetoelectric effect as a novel topological spin response.

cond-mat.mtrl-sci↗

arXiv2026

Majorana Zero Modes and Topological Nature in Bi2Ta3S6-family Superconductors

In this work, we report that Bi2Ta3S6-family superconductors exhibit nontrivial band topology. They possess a natural quantum-well structure consisting of alternating stacks of TaS2 and honeycomb Bi layers, which contribute superconducting and topological properties, respectively. Symmetry-based indicators $(\mathbb{Z}_4;\mathbb{Z}_{2}\mathbb{Z}_{2}\mathbb{Z}_{2})=(2;000)$ reveal that the topological nature arises entirely from the Bi layers, which belong to a quantum spin Hall phase characterized by a $p_x-p_y$ model on a honeycomb lattice. The topological zigzag (ZZ) and armchair (AC) edge states are obtained. Using VASP2KP, the in-plane $g$ factors of these topological edge states are computed from the ab initio calculations: $g_{x/y}^{\mathrm{ZZ}}=2.07/1.60$ and $g_{x/y}^{\mathrm{AC}}=0.50/0.06$. The strong anisotropy of the edge-state $g$ factors allows us to explore Majorana zero modes in the Bi monolayer on a superconductor, which can be obtained by exfoliation or molecular beam epitaxy. The relaxed structures of the Bi2Ta3Se6, Bi2Nb3S6 and Bi2Nb3Se6 are obtained. Their superconducting transition temperature $T_c$ are estimated based on the electron-phonon coupling and the McMillan formula. Furthermore, using the experimental superconducting gap $Δ$ and the computed $g$ factors, we obtain the phase diagram, which shows that the in-plane field $B_y>2.62\mathrm{ T}$ can generate corner Majorana zero modes in the Bi monolayer of the superconductor Bi2Ta3S6. A similar paradigm also applies to the Bi2Ta3S6 bulk with the emergence of Majorana hinge states. These natural quantum-well superconductors therefore offer ideal platforms for exploring topological superconductivity and Majorana zero modes.

cond-mat.supr-con↗

arXiv2025

Hidden Moiré Topology of Low-Symmetry Weyl Surfaces

Topological materials are defined by the correspondence between bulk topology and boundary states, yet this correspondence becomes enigmatic on low-symmetry surfaces where bulk and surface periodicities are inherently mismatched. Here we reveal a hidden moiré topology emerging on the (103) surface of the Weyl semimetal NdAlSi. Angle-resolved photoemission spectroscopy uncovers closed Fermi-arc loops and momentum-space moiré modulations, phenomena unanticipated in conventional topological theory. We show that these emerge from incomplete bulk projection and multi-cell interference governed by a least-common-multiple framework. Least-common-multiple guided DFT and Green's-function calculations quantitatively reproduce the observed spectra, establishing the universality of this commensuration rule. These findings transform a long-standing paradox of bulk-boundary correspondence into a new paradigm of momentum-space moiré reconstruction, bridging crystalline and quasicrystalline topologies and opening routes to flat-band engineering on complex surfaces.

cond-mat.mtrl-sci↗

arXiv2025

Quantum fluctuations associated with first-order magnetic transition in a frustrated kagome lattice antiferromagnet

Intense quantum fluctuations arising from geometrical frustrations in kagome-lattice magnets provide a feasible approach to exotic quantum states. Here, we document an unexpected isosymmetric first-order magnetic transition in the recently synthesized frustrated kagome-lattice antiferromagnet Nd3ScBi5, which is characterized by significant latent heat and a pronounced magnetocaloric effect, as well as discontinuous Raman shifts and negligible hysteresis. Employing the magnetocaloric effect as a detection method, in conjunction with systematical field-dependent physical properties, we uncover a distinctive 1/2 magnetization plateau phase with significant quantum fluctuations. Our study unveils Nd3ScBi5 as a prototypical model with an emerging phase of enhanced quantum fluctuations triggered by first-order magnetic transitions.

cond-mat.str-el↗

arXiv2025

Quasi-linear magnetoresistance and paramagnetic singularity in Hypervalent Bismuthide

Materials featuring hypervalent bismuth motifs have generated immense interest due to their extraordinary electronic structure and exotic quantum transport. In this study, we synthesized high-quality single crystals of La3ScBi5 characterized by one-dimensional hypervalent bismuth chains and performed a systematic investigation of the magnetoresistive behavior and quantum oscillations. The metallic La3ScBi5 exhibits a low-temperature plateau of electrical resistivity and quasi-linear positive magnetoresistance, with anisotropic magnetoresistive behaviors suggesting the presence of anisotropic Fermi surfaces. This distinctive transport phenomenon is perfectly elucidated by first-principles calculations utilizing the semiclassical Boltzmann transport theory. Furthermore, the nonlinear Hall resistivity pointed towards a multiband electronic structure, characterized by the coexistence of electron and hole carriers, which is further supported by our first-principles calculations. Angle-dependent de Haas-van Alphen oscillations are crucial for further elucidating its Fermiology and topological characteristics. Intriguingly, magnetization measurements unveiled a notable paramagnetic singularity at low fields, which might suggest the nontrivial nature of the surface states. Our findings underscore the interplay between transport phenomena and the unique electronic structure of hypervalent bismuthide La3ScBi5, opening avenues for exploring novel electronic applications.

cond-mat.mtrl-sci↗

arXiv2025

Stability Frontiers and Mixed-dimensional physics in the Kagome Intermetallics Ln3ScBi5 (Ln = La-Nd, Sm)

Low-dimensional physics provides profound insights into strongly correlated interactions, leading to enhanced quantum effects and the emergence of exotic quantum states. The Ln3ScBi5 family stands out as a chemically versatile kagome platform with mixed low-dimensional structural framework and tunable physical properties. Our research initiates with a comprehensive evaluation of the currently known Ln3ScBi5 (Ln = La-Nd, Sm) materials, providing a robust methodology for assessing their stability frontiers within this system. Focusing on Pr3ScBi5, we investigate the influence of the zigzag chains of quasi-one-dimensional (Q1D) motifs and the distorted kagome layers of quasi-two-dimensional (Q2D) networks in the mixed-dimensional structure on the intricate magnetic ground states and unique spin fluctuations. Our study reveals that the noncollinear antiferromagnetic (AFM) moments of Pr3+ ions are confined within the Q2D kagome planes, displaying minimal in-plane anisotropy. In contrast, a strong AFM coupling is observed within the Q1D zigzag chains, significantly constraining spin motion. Notably, the magnetic frustration is partially the consequence of coupling to conduction electrons via the Ruderman-Kittel-Kasuya Yosida (RKKY) interaction, highlighting a promising framework for future investigations into mixed-dimensional frustration in Ln3ScBi5 systems.

cond-mat.str-el↗

arXiv2025

Magnetization plateau and anisotropic magnetoresistance in the frustrated Kondo-lattice compound Ce3ScBi5

Kondo metals with geometric frustration offer fertile ground for exploring exotic states of matter with a field-induced fractional magnetization platform and nonsaturating magnetoresistance. Herein, a Ce3ScBi5 single crystal with anti-Hf5Sn3Cu hexagonal structure was successfully synthesized via the bismuth self-flux method, leading to the formation of cerium cations arranged in a frustrated structure within a distorted kagome lattice. Magnetic measurements exhibit two distinct antiferromagnetic transitions at 4.1 and 5.9 K. Specifically, the occurrence of multiple metamagnetic transitions between magnetization plateaus is evidenced upon applying magnetic fields perpendicular to the c axis. Transport measurements highlight remarkable Kondo-lattice characteristics and anisotropic magnetoresistance in Ce3ScBi5. The anomalous Hall contributions are observed at low temperatures under critical fields, suggesting Fermi surface reconstruction in a subset of the metamagnetic transitions. We have constructed a temperature-field phase diagram to provide comprehensive information on the complex magnetic structures arising from competitive interactions. Our work establishes Ce3ScBi5 and related materials as a unique platform for exploring low-dimensional quantum fluctuations in bulk crystals, and analyzes the critical role of geometric frustration in Kondo and Ruderman-Kittel-Kasuya-Yosida physical frameworks.

cond-mat.str-el↗

arXiv2025

MaterialsGalaxy: A Platform Fusing Experimental and Theoretical Data in Condensed Matter Physics

Modern materials science generates vast and diverse datasets from both experiments and computations, yet these multi-source, heterogeneous data often remain disconnected in isolated "silos". Here, we introduce MaterialsGalaxy, a comprehensive platform that deeply fuses experimental and theoretical data in condensed matter physics. Its core innovation is a structure similarity-driven data fusion mechanism that quantitatively links cross-modal records - spanning diffraction, crystal growth, computations, and literature - based on their underlying atomic structures. The platform integrates artificial intelligence (AI) tools, including large language models (LLMs) for knowledge extraction, generative models for crystal structure prediction, and machine learning property predictors, to enhance data interpretation and accelerate materials discovery. We demonstrate that MaterialsGalaxy effectively integrates these disparate data sources, uncovering hidden correlations and guiding the design of novel materials. By bridging the long-standing gap between experiment and theory, MaterialsGalaxy provides a new paradigm for data-driven materials research and accelerates the discovery of advanced materials.

cond-mat.mtrl-sci↗

arXiv2025

Chern-Selective multi-valley Flat Bands in Twisted Mono-Bilayer and Mono-Trilayer MoTe$_2$

The interplay between moiré flat bands originating from different valleys can give rise to a variety of exotic quantum phases. In this work, we investigate the electronic properties of twisted mono-bilayer (A-AB) and mono-trilayer (A-ABA) MoTe$_2$ using first-principles calculations and continuum models. Unlike previous studies on twisted bilayer systems, in which low-energy flat bands originate solely from the $K/K'$ valleys, in A-AB and A-ABA twisted MoTe$_2$ (\tmt) the moiré bands at low energies arise from both the $Γ$ and $K/K'$ valleys, with spin Chern numbers $C_s=0$ (for $Γ$) and $C_{\uparrow/\downarrow}=\pm1$ (for $K/K'$), respectively. We show that the multi-valley moiré flat bands are governed by interlayer-hybridization effects, and that different stacking configurations and thicknesses tune the relative energy alignment between the $Γ$ and $K$ valley moiré flat bands. By constructing valley-resolved continuum models and performing Wannierization for the low-energy moiré bands, we further uncover that the Berry curvature and quantum metric distributions can be effectively tuned by the layer number and stacking configuration. Unlike other moiré systems, where only one kind of valley influenced the low energy physics, the simultaneous appearance of two distinct types of valleys, with different symmetries, establish A-AB and A-ABA \tmt\ as ideal platforms for studying layer-controlled multi-valley physics.

cond-mat.mtrl-sci↗

arXiv2025

General First-Principles Approach to Crystals in Finite Magnetic Fields

We introduce a general first-principles methodology for computing electronic structure in a finite uniform magnetic field which allows for an arbitrary rational magnetic flux and nonlocal pseudopotentials, at a comparable time complexity of conventional plane-wave pseudopotential approaches in zero-field conditions. The versatility of this method is demonstrated through comprehensive applications to both molecular and crystalline systems, including calculations of magnetizabilities, magnetically induced currents, and magnetic energy bands. Furthermore, we provide rigorous proofs of two properties for crystals in uniform magnetic fields: the "strong translational symmetry" and "magnetic bands shift" phenomena.

cond-mat.mtrl-sci↗