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Gang Su

Publications and source records attributed to Gang Su.

At least 19 recordsLinked to original sources

Anomalous Thomson Effect

We formulate an effect called the anomalous Thomson effect (ATE), which constitutes the Thom?son counterpart to the anomalous Hall effect and anomalous Nernst effect (ANE). The anomalous Thomson coefficient (ATC) is determined by the anomalous Nernst coefficient (ANC) together with the temperature dependence of both the ANC and the longitudinal electrical conductivity; This relation is model independent within local linear response and holds for the total anomalous Nernst coefficient, irrespective of whether its microscopic origin is intrinsic or extrinsic. Specifically, we study a massive Dirac model for Fe3Sn2 to capture intrinsic Berry-curvature-driven transport, where the Berry curvature near the gapped Dirac cones enhances the ANC-related contributions to the ATC, and we also deduce the ATC from measured experimental data reported for CoS2,Co3Sn2S2, and CeCrGe3. In the low-temperature limit, the ratio ATC/ANC approaches three, and we find that the ATC for CeCrGe3 can be as large as ten times the ANC in the liquid-nitrogen temperature regime, making this effect highly attractive for solid-state thermoelectric refrigeration in this temperature range. It is important to emphasize that the formulated ATE can be directly verified using existing ANE and longitudinal conductivity data, without the need for additional equipment or measurements.

cond-mat.mes-hall

A Hamiltonian-Inspired Local-Operator Ansatz for Slimming Large Language Models

Dense linear maps carry much of the parameter and computational burden of modern neural networks, yet their dense form leaves the organization of learned couplings implicit. Quantum many-body physics organizes exponentially large operators by writing a global Hamiltonian as a sum of local terms, \(\hat H=\sum_k\hat h_k\). Whether the same structural principle can carry learned neural maps is unknown. We introduce Tensor Mixture (MixT), which represents a dense map as a natively executable sum of overlapping local tensor operators without imposing an explicit matrix-rank constraint. The local-term count \(N_T\) sets the effective nonlocality and operator complexity, while the number of replaced Transformer blocks \(N_B\) extends this structural coordinate across network depth. Tests on Qwen3-8B and LLaMA2-7B reveal a broad recoverable regime followed by an abrupt, model-specific boundary that is remarkably stable against changes in \(N_T\). Accuracy and output-distribution statistics reorganize together across the boundary; in LLaMA2-7B, the same depth separates two scaling regimes of inter-layer geometry drift. The directly executed structure also reduces parameters, arithmetic, storage, and memory. These results establish the local-sum structure as a viable organizing principle for learned linear maps at billion-parameter scale and expose a sharp boundary in their tolerance to structural simplification.

cs.CL

Anomalous Hall and Nernst effects driven by static and fluctuating spin chiralities on Kagome lattice

We theoretically investigate the anomalous Hall and Nernst effects (AHE and ANE) in a two dimensional Kagome lattice to uncover the distinct roles of static and fluctuating scalar spin chi ralities. Employing Monte Carlo simulations incorporating with a tight binding Hamiltonian via the s-d exchange interaction, we explicitly evaluate the anomalous transport coefficients. A key finding is the systematic disentanglement of the macroscopic responses into an intrinsic contribu tion, governed by momentum space Berry curvature induced by static chirality, and an extrinsic skew scattering contribution driven by real space dynamical spin fluctuations. We demonstrate a pronounced mechanistic crossover: deep in magnetically ordered phases like the skyrmion crystal, the intrinsic Berry curvature dictates the transport behavior. However, approaching the magnetic order-disorder critical regime, strong thermal fluctuations disrupt static noncoplanar spin configu rations, drastically suppressing intrinsic responses. Here, dynamical chiral fluctuations emerge as the dominant driving force. By delineating the phase regimes governed by static versus fluctuating chiralities, this work elucidates the distinct microscopic mechanisms dictating anomalous transport in frustrated magnetic systems.

cond-mat.str-el

Fundamental Relations as the Leading Order in Nonlinear Thermoelectric Responses with Time-Reversal Symmetry

In recent years, nonlinear transport phenomena have garnered significant interest in both theoretical explorations and experiments. In this work, we utilize the semi-classical wave packet theory to calculate disorder-induced second-order transport coefficients: second-order electrical ($σ$), thermoelectric ($α$), and thermal ($κ$) coefficients, capturing the interplay between side-jump and skew-scattering contributions in systems with time-reversal symmetry. Using a topological insulator model, we quantitatively characterize the Fermi-level dependence of these second-order transport coefficients by explicitly including Coulomb impurity potentials. Furthermore, we elucidate the relationships between these coefficients, establishing the second-order Mott relation and the Wiedemann-Franz law induced by disorder. This study develops a comprehensive theoretical framework elucidating the nonlinear thermoelectric transport mechanisms in quantum material systems.

cond-mat.mes-hall

Spontaneous emergence of altermagnetism in the single-orbital extended Hubbard model

Altermagnetism (AM), the recently discovered third class of collinear magnetic order, is characterized by non-relativistic momentum-dependent spin-split electronic structure with compensated zero net magnetization. It can arise from the conventional antiferromagnetism by introducing local anisotropy on the two opposite-spin sublattices, either through structural changes in local crystallographic symmetry or spontaneous emergence of local staggered orbital order from electron correlations in multi-orbital systems. Here, we demonstrate on the two-dimensional square lattice that a $d$-wave AM can emerge spontaneously in the single-orbital extended Hubbard model, without invoking crystallographic anisotropy and multi-orbital physics. We carry out mean-field studies on the concrete single-orbital $t$-$U$-$V$ model with $U$ and $V$ the onsite and nearest-neighbor Coulomb interactions, obtaining the mean-field ground states, analyzing their properties, and determining the phase diagram in the $U$-$V$ plane. The $d$-wave AM with novel spin-transport behavior is found to be stabilized in a wide region of the phase diagram when the system is doped away from half-filling, actualized by the coexistence of onsite antiferromagnetic order and complex $d$-wave nearest-neighbor spin bond orders. Our findings provide an alternative route to achieve AM and substantially expand the range of candidate AM materials.

cond-mat.str-el

Ising Supercriticality and Universal Magnetocalorics in Spiral Antiferromagnet Nd$_3$BWO$_9$

The celebrated analogy between the pressure-temperature phase diagram of a liquid-gas system and the field-temperature phase diagram of a ferromagnet has long been a cornerstone for understanding universality of phase transitions and critical phenomena. Here we extend this analogy to a highly frustrated antiferromagnet, the spiral Ising compound Nd$_3$BWO$_9$ with kagome layers. In its phase diagram, we identify a metamagnetic transition line with a critical endpoint (CEP) located at $μ_0H_{\mathrm{c}} \simeq 1.04$ T and $T_{\mathrm{c}} \simeq 0.3$ K. Above the CEP, an Ising supercritical regime emerges with crossover lines that follow a universal scaling law, as evidenced by the specific heat, magnetic susceptibility, and magnetocaloric measurements. Remarkably, we observe highly sensitive magnetic cooling near the emergent CEP, characterized by a divergent magnetic Grüneisen ratio $Γ_H \propto 1/t^{β+γ-1}$, with $β+ γ\simeq 1.563$ the sum of critical exponents of the 3D Ising universality class and $t \equiv (T-T_{\rm c})/T_{\rm c}$ the reduced temperature. Adiabatic demagnetization from 2 K and 4 T reaches a minimum temperature of 195 mK, via a self-cascading process that combines supercritical and topological cooling. Our findings open a new avenue for studying supercritical phenomena and magnetic refrigeration with the frustrated rare-earth compounds RE$_3$BWO$_9$ and, more broadly, in Ising-anisotropic antiferromagnets such as spin ices.

cond-mat.str-el

Correlated $\mathcal{PT}$-Symmetric Antiferromagnetic Topological Insulators with Giant Nonlinear Anomalous Thermoelectrics

Topological states in antiferromagnets (AFMs) offer a promising platform for exploring novel physical phenomena and advancing the applications of AFM spintronics. The AFM topological insulator (TI) state stands out as one of the most representative and prominent cases. Unlike the previously proposed AFM-TI states in noninteracting systems, here we employ an extended Kane-Mele-Hubbard model to demonstrate that electron correlations can give rise to a $\mathcal{PT}$-symmetric AFM-TI state. This state breaks both spatial inversion symmetry $\mathcal{P}$ and time-reversal symmetry $\mathcal{T}$, and enables intrinsic topological nonlinear responses to dominate the leading-order dynamics of the system. The competition between electron correlations and spin-orbit coupling drives the system across a topological phase transition, where the closure of the bulk band gap induces singular behaviors in higher-order quantum geometric tensors. Such microscopic singular characteristics manifest macroscopically as pronounced enhancements in thermoelectric performance, charge conductivity, and thermal conductivity. These giant tunable transport signatures, which can be effectively modulated by mechanical strain and electrostatic gating, provide a feasible experimental route to probe and understand correlated topological materials.

cond-mat.mes-hall

Bilateral hydrogenation induced high-Chern-number quantum anomalous Hall state in monolayer Cr$_2$Ge$_2$Te$_6$

The pursuit of high-temperature quantum anomalous Hall (QAH) insulators faces fundamental challenges, including narrow topological gaps and low Curie temperatures ($T_C$) in existing materials. Here, we propose a strategy using bilateral hydrogenation to engineer a robust QAH state in the topologically trivial ferromagnetic semiconductor Cr$_2$Ge$_2$Te$_6$ via covalent orbital reconstruction. First-principles calculations reveal that by rewiring the orbital hybridization network, hydrogenation alters orbital occupations to shift preexisting Dirac points, originally embedded in the conduction bands, to the vicinity of the Fermi level in Cr$_2$Ge$_2$Te$_6$H$_6$. This electronic restructuring, coupled with spin-orbit coupling, opens a global topological gap of 118.1 meV, establishing a robust QAH state with Chern number $C=3$. Concurrently, this orbital reconstruction tunes the energy difference between the ligand $p$ and transition metal $d$ orbitals. This shift enhances ferromagnetic superexchange via the $d{z^2}-p_z-d_{xz}$ channel, strengthening the nearest-neighbor coupling $J_1$ by 3.06 times and switching $J_2$ from antiferromagnetic to ferromagnetic. Monte Carlo simulations based on extracted exchange parameters indicate a pronounced enhancement of ferromagnetic stability compared with pristine Cr$_2$Ge$_2$Te$_6$. While absolute Curie temperatures depend on the mapping to an effective spin model and represent relative trends, the enhanced stability after hydrogenation is a salient effect. This work establishes targeted orbital reconstruction driven by surface hydrogenation as a powerful route to simultaneously control topology and magnetism in 2D materials, providing a general route to engineer QAH phases with large gaps and high Chern numbers in van der Waals ferromagnetic semiconductors.

cond-mat.mes-hall

Structural Alter-Phononics: Sublattice-Momentum Locking in Spinless Lattice Dynamics

The discovery of altermagnetism has shown that crystal symmetry can generate momentum-dependent internal polarization without net magnetization. Whether an analogous form of symmetry-organized momentum-space order can exist for spinless lattice vibrations remains unresolved. Here we identify a structural mechanism for $alter$-$phononics$, in which phonon eigenmodes formed from structurally equivalent sublattices acquire momentum-dependent sublattice polarization and frequency splitting in nonmagnetic crystals. The central quantity is the sublattice-resolved dynamical asymmetry $Δ(\mathbf q)=D_{AA}(\mathbf q)-D_{BB}(\mathbf q)$, which controls the associated eigenvector polarization. We show that this effect requires an alter-generator that maps equivalent sublattices onto one another while rotating the wave vector, together with the absence of inversion exchange and little-group sublattice-exchange constraints that would otherwise enforce sublattice equipartition. These symmetry rules generate nematic $d$-wave, tetragonal $d/g$-wave, and tripartite six-lobe phonon textures. First-principles calculations demonstrate the mechanism in representative nonmagnetic crystals and show how a symmetry-preserving structural distortion can unlock a hidden $d_{x^2-y^2}$-type texture by removing glide-induced equipartition traps while retaining the screw-axis alter-generator. We further show that the eigenvector texture is inherited by sublattice-projected electron-phonon coupling and anharmonic response functions. Our results establish structural alter-phononics as a spinless counterpart to altermagnetic momentum-space order and provide experimentally testable signatures in finite-$\mathbf q$ phonon spectra and displacement patterns.

cond-mat.mtrl-sci

$5/9-$Magnetization Plateau and Spin Supersolidity in YCu$_3$(OD)$_{7-x}$Br$_{2+x}$ under Magnetic Fields up to 120~T

We performed high-precision magnetization measurements up to 120~T on three compositions of the newly discovered kagome antiferromagnet YCu$_3$(OD)$_{7-x}$Br$_{2+x}$ (YCOB), revealing a previously unobserved 5/9 fractional magnetization plateau. All YCOB samples with different Br$^-$ concentrations exhibit nearly identical magnetization curves below 60~T, whereas the 5/9 plateau appears at markedly different fields in the ultrahigh-field regime. By modeling the experimental data using tensor-network calculations, we derive the effective spin Hamiltonians for the YCOB family with three spatially anisotropic Heisenberg couplings (the 3$J$-type model), which quantitatively reproduces the measured magnetization processes and captures the composition-dependent evolution of the 5/9 plateau. Furthermore, our theoretical analysis suggests the emergence of a spin supersolid phase in the field window between the 1/3 and 5/9 plateaus, which is sensitive to spin exchange parameters and accounts for the significant variation in the critical fields of the 5/9 plateau observed among different YCOB compositions.

cond-mat.str-el

RKKY-dipolar Interactions and 3D Spin Supersolid on Stacked Triangular Lattice

Inspired by the recent discovery of metallic spin supersolidity and its giant magnetocaloric effect in the rare-earth alloy EuCo$_2$Al$_9$ [Nature 651, 61 (2026)], we perform a combined study through electronic structure analysis, effective spin model, and Monte Carlo simulations on a stacked triangular lattice, and reveal a novel mechanism for the emergence of 3D spin supersolid in a metallic antiferromagnet. From first-principles inputs, we derive a minimal spin model on a stacked triangular lattice (STL), which arises from the interplay between Ruderman-Kittel-Kasuya-Yosida (RKKY) and dipolar interactions and accurately reproduces the experimental thermodynamics. Based on the STL model, we identify a ground state that simultaneously breaks discrete lattice translational symmetry and continuous spin-rotational symmetry -- the hallmark of a spin supersolid. Furthermore, we present the field-temperature phase diagram of the 3D STL model and discuss the various magnetic phases and associated phase transitions. Under zero field, the spin supersolid Y order establishes in two steps: an upper transition at $T_{N1}$, where an emergent U(1) symmetry appears and the system enters a fluctuating collinear regime, followed by a lower transition at $T_{N2}$ into the spin supersolid Y phase. In contrast, the supersolid V phase undergoes a single phase transition at $T_N^V$. Our results not only provide a comprehensive theoretical understanding of the metallic spin supersolid reported for EuCo$_2$Al$_9$ but also pave the way for further experimental investigations into its supersolid transitions and universality class.

cond-mat.str-el

$\mathrm{Cs_3V_9Te_{13}}$: A New Vanadium-Based Material with a Reuleaux-Triangle-Like Lattice and a Possible Phase Transition near 48 K

Exploring and synthesizing materials with new crystal structures provides an important route to discovering exotic quantum phenomena. However, materials with unconventional lattice geometries remain largely unexplored. Here, we report the discovery of a new vanadium-based material, $\mathrm{Cs_3V_9Te_{13}}$, featuring a Reuleaux-triangle-like lattice. Electrical transport and magnetic measurements consistently reveal an anomaly near 48 K, and this feature shows little sensitivity to the applied magnetic field. A corresponding anomaly is also observed in the Hall coefficient near 48 K, indicating a marked change in the carrier response. In addition, temperature-dependent x-ray diffraction results indicate no obvious structural change across 48 K. Taken together, these results suggest that the anomaly is not induced by the structural transition, but associated to a possible electronic and/or magnetic phase transition. High-pressure transport measurements and first-principles calculations further reveal a highly tunable electronic state in $\mathrm{Cs_3V_9Te_{13}}$, with the kagome-like electronic feature and pressure-suppressed antiferromagnetism. These results demonstrate this material, with its structurally novel Reuleaux-triangle-like lattice, as a new platform for exploring the interplay between nontrivial lattice geometry and emergent physical phenomena.

cond-mat.mtrl-sci

Matrix-product entanglement characterizing the optimality of state-preparation quantum circuits

Multipartite entanglement offers a powerful framework for understanding the complex collective phenomena in quantum many-body systems that are often beyond the description of conventional bipartite entanglement measures. Here, we propose a class of multipartite entanglement measures that incorporate the matrix product state (MPS) representation, enabling the characterization of the optimality of quantum circuits for state preparation. These measures are defined as the minimal distances from a target state to the manifolds of MPSs with specified virtual bond dimensions $χ$, and thus are dubbed as $χ$-specified matrix product entanglement ($χ$-MPE). We demonstrate superlinear, linear, and sublinear scaling behaviors of $χ$-MPE with respect to the negative logarithmic fidelity $F$ in state preparation, which correspond to excessive, optimal, and insufficient circuit depth $D$ for preparing $χ$-virtual-dimensional MPSs, respectively. Specifically, a linearly-growing $χ$-MPE with $F$ suggests $\mathcal{H}_χ \simeq \mathcal{H}_{D}$, where $\mathcal{H}_χ$ denotes the manifold of the $χ$-virtual-dimensional MPSs and $\mathcal{H}_{D}$ denotes that of the states accessible by the $D$-layer circuits. We provide an exact proof that $\mathcal{H}_{χ=2} \equiv \mathcal{H}_{D=1}$. Our results establish tensor networks as a powerful and general tool for developing parametrized measures of multipartite entanglement. The matrix product form adopted in $χ$-MPE can be readily extended to other tensor network ansätze, whose scaling behaviors are expected to assess the optimality of quantum circuit in preparing the corresponding tensor network states.

quant-ph

Odd-even parity dependent transport in an annular Kitaev chain

We investigate the impact of magnetic flux and the odd-even parity of lattice points $N$ on electron transport in an annular Kitaev chain, with an explanation provided from the energy band perspective. Three transport mechanisms including direct transmission (DT), local Andreev reflection (LAR) and crossed Andreev reflection (CAR) are considered. In particular, the connection configuration of electrodes to different lattice sites is studied, where the case that the two electrodes connected to the sites are aligned along a diameter is called as symmetric connection and otherwise as asymmetric connections. For even $N$ and asymmetric connection, the vanished LAR and CAR in symmetric connection will emerge as peaks. A more prominent observation is that the symmetry of the two resonant peaks due to DT processes located at $Φ= Nπ/3$ and $Φ= 2Nπ/3$ for symmetric connection will be broken, and the peak at $Φ= Nπ/3$ will be largely reduced, where $Φ$ is the magnetic flux. Moreover, the peaks around $Φ= Nπ/3$ due to LAR and CAR processes grows drastically even larger than that from DT. For LAR and CAR processes, there is no peak around $Φ= 2Nπ/3$ and transmission due to these two processes are completely suppressed for $Φ>Nπ/2$. Moreover, it is found that the energy bands vary with $Φ$ in a period of $Nπ$ and $2Nπ$ for even or odd $N$. We finally systematically analyze the influence of weak disorder on transport and demonstrate that these parity-dependent effects are robust in the presence of disorder. These behaviors reflect a complicated competition from DT, LAR and CAR processes and the parity of the lattice number in the Kitaev ring, which will be interested for the quantum device based on Kitaev chain.

cond-mat.supr-con

$d$-wave FFLO state and charge-2e supersolidity in the $t$-$t'$-$J$ model under Zeeman fields

Unconventional superconductivity under strong Zeeman fields--particularly beyond the Pauli paramagnetic limit--remains a central challenge in condensed matter physics. The exotic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, in particular, remains in need of definitive study within fundamental electronic models. Here we employ state-of-the-art finite-temperature and ground-state tensor network approaches to systematically explore the superconducting (SC) phase diagram of the $t$-$t'$-$J$ model subjected to Zeeman fields. We find that zero-momentum $d$-wave superconductivity persists until the spin gap closes, coexisting with charge density waves. A novel $d$-wave FFLO phase emerges under a higher Zeeman field even above the Pauli limit, concomitant with a field-enhanced spin density waves. We identify these phases, characterized by the simultaneous presence of pairing condensate and density wave orders, as charge-2e supersolids. Analysis of Matsubara Green's function reveals that the FFLO pairing momentum is locked to the underlying Fermi surface. Our results provide microscopic insights into field-induced unconventional pairing mechanisms and reveal the long-sought FFLO state in a fundamental correlated electron model, offering a promising route for its realization in ultracold atom optical lattice.

cond-mat.str-el

Dominant Kitaev Interaction and Field-induced Quantum Disordered Phase in the Cobaltate Na$_2$Co$_2$TeO$_6$

The identification of quantum spin liquid phases in Kitaev candidate materials remains a major experimental challenge. Since most Kitaev candidates develop antiferromagnetic (AFM) order at low temperatures, currently there are great interest on the field-induced magnetic disordered phase in these compounds, that are distinct from (partially) polarized states. Recently, a cobaltate Na$_2$Co$_2$TeO$_6$ has emerged as a promising Kitaev candidate with high-spin $t^{5}_{2g}e^2_g$ configuration and spin-orbit entangled $J_{\rm eff} = 1/2$ honeycomb lattice system. There are intensive studies on field-induced magnetic states and phase transitions under in-plane magnetic fields. In this study, we propose an intermediate disordered phase induced by an out-of-plane field along the $c$-axis, through high-field magnetization and magnetocaloric effect measurements. To explain the high-field behavior of Na$_2$Co$_2$TeO$_6$, we develop an effective $K$-$J$-$Γ$-$Γ^{\prime}$ spin model featuring a dominant AFM Kitaev interaction. This framework uncovers an intermediate quantum spin liquid phase, establishing the material as a unique platform for exploring Kitaev physics and field-induced quantum-disordered states.

cond-mat.str-el

Spin PN Junctions: Giant Magnetoresistance, Tunable Circular Polarization, and Spin Zener Filter

We demonstrate that spin PN junctions-magnetic semiconductor homojunctions with spin splitting-induced band offsets-fundamentally redefine carrier transport via spin-dependent recom bination probabilities. By integrating this mechanism into the Shockley model, we predict a near 100 enhancement in magnetoresistance sensitivity under small forward bias, where exponen tial modulation of recombination lifetimes by magnetic fields amplifies resistance changes. Angular momentum conservation enables magnetically tunable circularly polarized luminescence: exclusive conduction-band or valence-band splitting in both neutral regions achieves near-half po larization, while global splitting degrades emission coherence. Furthermore, we propose a "spin Zener filter" exploiting 1eV valence band splitting in (Ga, Mn)As, where spin-dependent barrier heights generate near 100% spin-polarized tunneling currents within a voltage-selective win dow. These results establish spin PN junctions as a universal design paradigm for magnetically amplified electronics, polarization-programmable optoelectronics, and voltage-gated spin injection without ferromagnetic contacts.

cond-mat.mtrl-sci

Diameter-Controlled High-Order Vortex States and Magnon Hybridization in VSe2 Nanotubes

Curved magnets offer a rich phase diagram and hold great promise for next-generation spintronic technologies. This study establishes the paramount significance of high-order vortex states (e.g., 3$φ$ with winding number $n$ > 1) in VSe2 nanotubes, which uniquely enable magnonic functionalities fundamentally inaccessible to conventional magnetic systems. These states arise from diameter-dependent competition between the nearest-neighbor ferromagnetic ($J_1$) and longer-range antiferromagnetic ($J_2$/$J_3$) couplings, as rigorously validated through density-functional theory calculations and Heisenberg modeling of phase diagrams. Critically, by the Landau-Lifshitz-Gilbert equation, we find that high-order vortex configurations unlock an intrinsic hybridization mechanism governed by strict orbital angular momentum (OAM) selection rules ($Δl = \pm 2(n-1)$) -- a process strictly forbidden in fundamental vortices ($n$ = 1) -- generating complex high-OAM magnons with measurable topological charge. This is vividly demonstrated in the 3$φ$ state, where hybridization between $l$ = -4, 0 and 4 modes produces eight-petal magnon density patterns. Such states provide an essential platform-free solution for generating high-OAM magnons, wchich is crucial for spin-wave-based information transport. These findings establish a predictive theoretical framework for controlling high-order vortex states in curved magnets and highlight VSe2 nanotubes as a promising platform for exploring complex magnetism and developing future magnonic and spintronic devices.

cond-mat.mtrl-sci