arXiv subjects

Xiang-Long Yu

Publications and source records attributed to Xiang-Long Yu.

17 recordsLinked to original sources

arXiv2026

Three-Band Anderson Lattice Model Reveals Co-Evolution of Topological and Magnetic Phases Driven by Electron Correlation

Understanding the interplay of band topology, strong electron correlation, and magnetic order is the fundamental core bottleneck for realizing robust high-temperature quantum anomalous Hall effect (QAHE). Conventional two-band Anderson models are limited to paramagnetic Kondo topological insulators, failing to capture coupled topological-magnetic phase evolution relevant to the QAHE benchmark MnBi2Te4 family. We develop a minimal three-band Anderson lattice model incorporating Hubbard interaction, s-d exchange coupling, and a BHZ-like topological mechanism. Using the Kotliar-Ruckenstein slave-boson approach, we map correlation-driven phase transitions at filling v=2: increasing U drives a trivial-to-Kondo topological insulator transition, then activates the third band to mediate a paramagnetic topological insulator-to-ferromagnetic metal transition. The accompanying band reconstruction--fully spin-polarized d-orbitals sinking below the Fermi level, leaving itinerant p-orbitals to dominate low-energy physics--qualitatively matches published first-principles results for MnBi2Te4. In the strong-correlation regime, exchange coupling J stabilizes a Chern-Kondo insulator (C=1) and Weyl nodal-line semimetal. Critically, we reveal full d-orbital spin polarization renders the topological gap immune to correlation-induced narrowing, resolving the long-standing strong correlation-large gap incompatibility. Our results show excellent qualitative alignment with recent state-of-the-art QAHE experiments, providing a unified framework for correlated magnetic topological materials and new pathways to high-temperature QAHE.

cond-mat.str-el↗

arXiv2026

Intrinsic Spin Filter Effect in a $d$-wave altermagnet KV$_2$Se$_2$O with Open Fermi Surface

Altermagnets offer a unique pathway to functional spintronics by combining vanishing magnetization with large spin splitting. Here, we demonstrate that the canonical d-wave altermagnet KV2Se2O can deliver giant tunneling magnetoresistance through orientation-dependent spin filtering. By analyzing the crystallographic spin segregation, we show that transport along specific crystallographic axes is nearly fully spin-polarized within the symmetry-protected ballistic channels. We implement this mechanism in a lattice-matched KV2Se2O/Bi2O2Se/KV2Se2O magnetic tunnel junction, which achieves a robust half-metallic transport regime. The symmetry-protected spectral gap in the parallel/anti-parallel configuration ensures a high tunneling magnetoresistance ratio, resulting in substantial tunneling magnetoresistance, robust thermally driven spin filtering, and spin Seebeck effect at room temperature. These findings provide a path of altermagnetic heterostructures as a high-performance platform for scalable, field-free, and thermally stable spin logic.

cond-mat.mtrl-sci↗

arXiv2025

Unveiling the Phase Diagram and Nonlinear Optical Responses of a Twisted Kitaev Chain

Detecting Kitaev interactions in real materials remains challenge, as conventional experimental techniques often have difficulty distinguishing fractionalized excitations from other normal contributions. Terahertz two-dimensional coherent spectroscopy (2DCS) offers a novel approach for probing many-body phenomena, such as exotic excitations in quantum magnets. Motivated by recent experiments on CoNb$_2$O$_6$ and the development of the terahertz spectroscopy in Kitaev quantum spin liquid, we proposed a twisted Kitaev model for CoNb$_2$O$_6$ and determined the precise twist angle according to experimental specific-heat phase diagram. With this calibrated model, we found that non-rephasing diagonal and rephasing anti-diagonal signals appear in the 2DCS nonlinear response. The $x$ and $y$ components of the spin superexchange interactions split the rephasing signals into a grid of discrete peaks. We further demonstrate that the diagonal and the discrete rephasing signals primarily originate from two-spinon and four-spinon excitation processes based on numerical projection method. These findings indicate that even weak Kitaev interactions in quantum materials can be effectively detected via two-dimensional coherent spectroscopy .

cond-mat.str-el↗

arXiv2025

All-electrically controlled spintronics in altermagnetic heterostructures

The recent discovery of altermagnets, which exhibit spin splitting without net magnetization, opens new directions for spintronics beyond the limits of ferromagnets, antiferromagnets, and spin orbit coupled systems. We investigate spin selective quantum transport in heterostructures composed of a normal metal and a two dimensional d-wave altermagnet, and identify a universal mechanism for achieving perfect spin polarization. The mechanism is dictated by Fermi surface geometry: closed Fermi surfaces in weak altermagnets yield partial and oscillatory spin filtering, whereas open Fermi surfaces in strong altermagnets intrinsically enforce fully spin polarized conductance. Exploiting these distinct transport regimes, we propose all electrical spin filter and spin valve architectures, where resonant tunneling produces highly spin polarized conductance tunable by gate voltage and interface transparency. Altermagnets with open Fermi surfaces further support gate reversible perfect spin polarization that remains robust against interface scattering, disorder, and temperature. We also demonstrate an electrically controlled spin valve that reproduces the functionality of magnetic tunnel junctions without magnetic fields or relativistic mechanisms. d-wave altermagnets with open Fermi surfaces thus provide a promising platform for low dissipation, scalable, and magnetic field free spintronic devices with potential for integration into next generation quantum and CMOS compatible technologies.

cond-mat.mes-hall↗

arXiv2024

Floquet engineering of topological phase transitions in quantum spin Hall $\alpha$-$T_{3}$ system

Floquet engineering of topological phase transitions driven by a high-frequency time-periodic field is a promising approach to realizing new topological phases of matter distinct from static states. Here, we theoretically investigate Floquet engineering topological phase transitions in the quantum spin Hall $\alpha$-$T_{3}$ system driven by an off-resonant circularly polarized light. In addition to the quantum spin (anomalous) Hall insulator phase with multiple helical (chiral) edge states, spin-polarized topological metallic phases are observed, where the bulk topological band gap of one spin sub-band overlaps with the other gapless spin sub-band. Moreover, with a staggered potential, the topological invariants of the system depend on whether the middle band is occupied because of the breaking of symmetry with respect to the center of energy-momentum plane. Our work highlights the significance of Floquet engineering in realizing new topological phases in $\alpha$-$T_{3}$ lattices.

cond-mat.mes-hall↗

arXiv2024

Interlayer ferroelectric polarization modulated anomalous Hall effects in four-layer MnBi2Te4 antiferromagnets

Van der Waals (vdW) assembly could efficiently modulate the symmetry of two-dimensional (2D) materials that ultimately governs their physical properties. Of particular interest is the ferroelectric polarization being introduced by proper vdW assembly that enables the realization of novel electronic, magnetic and transport properties of 2D materials. Four-layer antiferromagnetic MnBi2Te4 (F-MBT) offers an excellent platform to explore ferroelectric polarization effects on magnetic order and topological transport properties of nanomaterials. Here, by applying symmetry analyses and density-functional-theory calculations, the ferroelectric interface effects on magnetic order, anomalous Hall effect (AHE) or even quantum AHE (QAHE) on the F-MBT are analyzed. Interlayer ferroelectric polarization in F-MBT efficiently violates the PT symmetry (the combination symmetry of central inversion (P) and time reverse (T) of the F-MBT by conferring magnetoelectric couplings, and stabilizes a specific antiferromagnetic order encompassing a ferromagnetic interface in the F-MBT. We predict that engineering an interlayer polarization in the top or bottom interface of F-MBT allows converting F-MBT from a trivial insulator to a Chern insulator. The switching of ferroelectric polarization at the middle interfaces results in a direction reversal of the quantum anomalous Hall current. Additionally, the interlayer polarization of the top and bottom interfaces can be aligned in the same direction, and the switching of polarization direction also reverses the direction of anomalous Hall currents. Overall, our work highlights the occurrence of quantum-transport phenomena in 2D vdW four-layer antiferromagnets through vdW assembly. These phenomena are absent in the bulk or thin-film in bulk-like stacking forms of MnBi2Te4.

cond-mat.mtrl-sci↗

arXiv2023

Midgap states induced by Zeeman field and $p$ wave superconductor pairing

The one-dimensional Su-Schrieffer-Heeger (SSH) model is central to band topology in condensed matter physics, which allows us to understand and design distinct topological states. In this work, we find another mechanism to analogize the SSH model in a spinful system, realizing an obstructed atomic insulator by introducing intrinsic spin-orbit coupling and in-plane Zeeman field. In our model, the midgap states originate from a quantized hidden polarization with invariant index $\mathbb{Z}_2$ (0; 01) due to the local inversion symmetry breaking. When the global inversion symmetry is broken, a charge pumping is designed by tuning the polarization. Moreover, by introducing the $p+ip$ superconductor pairing potential, a new topological phase dubbed obstructed superconductor (OSC) is identified. This new state is characterized by invariant index $\mathbb{Z}_2$ (0; 01) and nonchiral midgap states. More interestingly, these nonchiral edge states result in a chiral-like nonlocal conductance, which is different from the traditional chiral topological superconductor. Our findings not only find another strategy to achieve a spinful SSH model but also predict the existence of OSC, providing a promising avenue for further exploration of its transport properties.

cond-mat.mes-hall↗

arXiv2023

Three consecutive quantum anomalous Hall gaps in a metal-organic network

In the quantum anomalous Hall (QAH) effect, chiral edge states are present in the absence of magnetic fields due to the intrinsic band topology. In this work, we predict that a synthesized two-dimensional metal-organic material, a Fe(biphenolate)$_3$ network, can be a unique QAH insulator, in which there are three consecutive nontrivial bandgaps. Based on first-principles calculations with effective model analysis, we reveal such nontrivial topology is from the $3$d$_{xz}$ and $3$d$_{yz}$ orbitals of Fe atoms. Moreover, we further study the effect of substrates, and the results shows that the metallic substrates used in the experiments (Ag and Cu) are unfavorable for observing the QAH effect whereas a hexagonal boron nitride substrate with a large bandgap may be a good candidate, where the three consecutive QAH gaps appear inside the substrate gap. The presence of three consecutive bandgaps near the Fermi level will significantly facilitate observations of the QAH effect in experiments.

cond-mat.str-el↗

arXiv2023

Possible high-temperature magnetically topological material Mn$_{3}$Bi$_{2}$Te$_{6}$

The Mn-Bi-Te family displaying magnetism and non-trivial topological properties has received extensive attention. Here, we predict that the antiferromagnetic structure of Mn$_{3}$Bi$_{2}$Te$_{6}$ with three MnTe layers is energetically stable and the magnetic coupling strength of Mn-Mn is enhanced four times compared with that in the single MnTe layer of MnBi$_{2}$Te$_{4}$. The predicted N\'eel transition point is higher than 77 K, the liquid-nitrogen temperature. The topological properties show that with the variation of the MnTe layer from a single layer to three layers, the system transforms from a nontrivial topological phase to a trivial topological phase. Interestingly, the ferromagnetic state of Mn$_{3}$Bi$_{2}$Te$_{6}$ is a topological semimetal and it exhibits a topological transition from trivial to nontrivial induced by the magnetic transition. Our results enrich the Mn-Bi-Te family system, offer a new platform for studying topological phase transitions, and pave a new way to improve the working temperature of magnetically topological devices.

cond-mat.str-el↗

arXiv2022

Direct Measurement of Topological Number by Quench Dynamics

The measurement of topological number is crucial in the research of topological systems. Recently, the relations between the topological number and the dynamics are built. But a direct method to read out the topological number via the dynamics is still lacking. In this work, we propose a new dynamical protocol to directly measure the topological number of an unknown system. Different from common quench operations, we change the Hamiltonian of the unknown system to another one with known topological properties. After the quench, different initial states result in different particle number distributions on the post-quench final Bloch bands. Such distributions depend on the wavefunction overlap between the initial Bloch state and the final Bloch state, which is a complex number depending on the momentum. We prove a theorem that when the momentum varies by $2\pi$, the phase of the wavefunction overlap change by $\Delta n\pi$ where $\Delta n$ is the topological number difference between the initial Bloch band and the final Bloch band. Based on this and the known topological number of the final Bloch band, we can directly deduce the topological number of the initial state from the particle number distribution and need not track the evolution of the system nor measure the spin texture. Two experimental schemes are also proposed as well. These schemes provide a convenient and robust measurement method and also deepens the understanding of the relation between topology and dynamics.

quant-ph↗

arXiv2020

Quantum dynamical characterization and simulation of topological phases with high-order band inversion surfaces

How to characterize topological quantum phases is a fundamental issue in the broad field of topological matter. From a dimension reduction approach, we propose the concept of high-order band inversion surfaces (BISs) which enable the optimal schemes to characterize equilibrium topological phases by far-from-equilibrium quantum dynamics, and further report the experimental simulation. We show that characterization of a d-dimensional (dD) topological phase can be reduced to lower-dimensional topological invariants in the high-order BISs, of which the nth-order BIS is a (d-n)D interface in momentum space. In quenching the system from trivial phase to topological regime, we unveil a high-order dynamical bulk-surface correspondence that the quantum dynamics exhibits nontrivial topological pattern in arbitrary nth-order BISs, which universally corresponds to and so characterizes the equilibrium topological phase of the post-quench Hamiltonian. This high-order dynamical bulk-surface correspondence provides new and optimal dynamical schemes with fundamental advantages to simulate and detect topological states, in which through the highest-order BISs that are of zero dimension, the detection of topological phase relies on only minimal measurements. We experimentally build up a quantum simulator with spin qubits to investigate a 3D chiral topological insulator through emulating each momentum one by one and measure the high-order dynamical bulk-surface correspondence, with the advantages of topological characterization via highest-order BISs being demonstrated.

cond-mat.mes-hall↗

arXiv2017

From a normal insulator to a topological insulator in plumbene

Plumbene, similar to silicene, has a buckled honeycomb structure with a large band gap ($\sim 400$ meV). All previous studies have shown that it is a normal insulator. Here, we perform first-principles calculations and employ a sixteen-band tight-binding model with nearest-neighbor and next-nearest-neighbor hopping terms to investigate electronic structures and topological properties of the plumbene monolayer. We find that it can become a topological insulator with a large bulk gap ($\sim 200$ meV) through electron doping, and the nontrivial state is very robust with respect to external strain. Plumbene can be an ideal candidate for realizing the quantum spin Hall effect at room temperature. By investigating effects of external electric and magnetic fields on electronic structures and transport properties of plumbene, we present two rich phase diagrams with and without electron doping, and propose a theoretical design for a four-state spin-valley filter.

cond-mat.mtrl-sci↗

arXiv2014

Orbital density wave order and electronic correlation driven insulating 1T-TaS2 monolayer

We present the orbital resolved electronic properties of structurally distorted 1T-TaS2 monolayers. After optimizing the crystal structures, we obtain the lattice parameters and atomic positions in the star-of-David structure, and show the low-temperature band structures of distorted bulk are consistent with recent angle resolved photoemission spectroscopy (ARPES) data. We further clearly demonstrate that $5d$ electrons of Ta form ordered orbital-density-wave (ODW) state with dominant $5d_{3{z}^2-{r}^2}$ character in central Ta, driving the one-dimensional metallic state in paramagnetic bulk and half-filled insulator in monolayer. Meanwhile, the star-of-David distortion in monolayers favors charge density wave and the flat band stabilizes ferromagnetic density wave of Ta spins with the same wavevector of ODW 4/13 b_1+1/13 b2. We propose that $1$T-TaS$_{2}$ monolayer may pave a new way to study the exciton physics, exciton-polaron coupling, and potential applications for its exciton luminescence.

cond-mat.str-el↗

arXiv2014

Coexistence of localized and itinerant magnetism in newly discovered iron-selenide superconductor LiFeO2Fe2Se2

The electronic structure and magnetism of LiFeO$_{2}$Fe$_{2}$Se$_{2}$ are investigated using the first-principle calculations. The ground state is N$\acute{e}$el antiferromagnetic (AFM) Mott insulating state for Fe1 with localized magnetism in LiFeO$_{2}$ layer and striped AFM metallic state for Fe2 with itinerant magnetism in Fe$_{2}$Se$_{2}$ layer, accompanied with a weak interlayer AFM coupling between Fe1 and Fe2 ions, resulting in a coexistence of localized and itinerant magnetism. Moreover, the layered LiFeO$_{2}$ is found to be more than an insulating block layer but responsible for enhanced AFM correlation in Fe$_{2}$Se$_{2}$ layer through the interlayer magnetic coupling. The interplay between the magnetisms of Fe1 and Fe2 introduces a control mechanism for spin fluctuations associated with superconductivity in iron-based superconductors.

cond-mat.supr-con↗

arXiv2014

A site-selective antiferromagnetic ground state in layered pnictide-oxide BaTi2As2O

The electronic and magnetic properties of BaTi$_{2}$As$_{2}$O have been investigated using both the first-principles and analytical methods. The full-potential linearized augmented plane-wave calculations show that the most stable state is a site-selective antiferromagnetic (AFM) metal with a $\text{2}\times \text{1}\times \text{1}$ magnetic unit cell containing two nonmagnetic Ti atoms and two other Ti atoms with antiparallel moments. Further analysis to Fermi surface and spin susceptibility shows that the site-selective AFM ground state is driven by the Fermi surface nesting and the Coulomb correlation. Meanwhile, the charge density distribution remains uniform, suggesting that the phase transition at $200$ K in experiment is a spin-density-wave (SDW) transition.

cond-mat.supr-con↗

arXiv2013

Ground-state and finite-temperature properties of spin liquid phase in the J1-J2 honeycomb model

In this paper we analyze the groundstate and finite-temperature properties of a frustrated Heisenberg $J_1-J_2$ model on a honeycomb lattice by employing the Schwinger boson technique. The phase diagram and spin gap as functions of ${J}_{2}/{J}_{1}$ are presented, showing that the exotic spin liquid phase lies in $0.21<{J}_{2}/{J}_{1} <0.43$. The temperature and magnetic-field dependences of specific heat, magnetic susceptibility and Knight shift are also presented. We find the spin liquid state is robust with respect to external magnetic field. These results provide clear information characterizing unusual properties of the exotic spin liquid phase for further experiments.

cond-mat.str-el↗

arXiv2012

Band-filling and correlation controlling electronic properties and magnetism in K$_{x}$Fe$_{2-y}$Se$_{2}$: A slave boson study

In this paper we investigate the electronic and magnetic properties of K$_{x}$Fe$_{2-y}$Se$_{2}$ materials at different band fillings utilizing the multi-orbital Kotliar-Ruckenstein's slave-boson mean field approach. We find that at three-quarter filling, corresponding to KFe$_{2}$Se$_{2}$, the ground state is a paramagnetic bad metal. Through band renormalization analysis and comparison with the angle-resolved photoemission spectra data, we identify that KFe$_{2}$Se$_{2}$ is also an intermediate correlated system, similar to iron-pnictide systems. At two-third filling, corresponding to the Fe$^{2+}$-based systems, the ground state is a striped antiferromagnetic (SAFM) metal with spin density wave gap partially opened near the Fermi level. In comparison, at half filling case, corresponding to the Fe$^{3+}$-based compounds, besides SAFM, a $N\acute{e}el$ antiferromagnetic metallic ground state without orbital ordering is observed in the intermediate correlation range, and an orbital selective Mott phase (OSMP) accompanied with an intermediate-spin to high-spin transition is also found. These results demonstrate that the band filling and correlation control the electronic state, Fermi surface topology and magnetism in K$_{x}$Fe$_{2-y}$Se$_{2}$.

cond-mat.supr-con↗