arXiv subjects

Dong-Hui Xu

Publications and source records attributed to Dong-Hui Xu.

At least 19 recordsLinked to original sources

arXiv2026

Topological surface altermagnets in SSH-stacked magnetic layers

Surface altermagnetism opens new avenues in spintronics by unlocking altermagnetic spin-splitting at the boundaries of conventional antiferromagnets, bypassing the strict symmetry requirements of bulk altermagnets. In this work, we propose creating topological surface altermagnet by stacking magnetic layers in a Su-Schrieffer-Heeger pattern. We show that while the bulk of the system is a standard antiferromagnet with degenerate bands protected by $PT$ symmetry, breaking the local symmetry at the boundary gives rise to a topologically protected surface altermagnetic state residing within the topological gap. Furthermore, we propose that this effect can be experimentally detected by applying a perpendicular electric field. Besides, this approach can be readily generalized to surface altermagnetism of different types. Our work establishes topological boundaries as a natural platform for surface altermagnetism, offering a distinct route for realizing and manipulating topological surface altermagnets.

cond-mat.mes-hall↗

arXiv2026

The odd-parity altermagnetism induced reconstruction of the Chern-insulating phase in Haldane-Hubbard model

Odd-parity altermagnetism(ALM) extends compensated collinear magnetism beyond the even-parity spin splitting of conventional altermagnets, but its role in correlated topological phases remains largely unexplored. Using the cluster slave-spin method, we show that the odd-parity ALM appearing in the ALM Chern-insulating phase of Haldane-Hubbard model significantly reconstructs the local topology in the conventional Chern-insulating phase, while the total Chern number remains unchanged compared to the Chern-insulating phase. The Berry curvature becomes spin and valley selective; zigzag ribbons develop chiral-symmetry-breaking edge states; while armchair ribbons remain inversion symmetric. The optical response mirrors this separation between the local reconstruction and the global topology: low-energy spectra are governed by quasiparticles near the gap, whereas the low-frequency Hall conductivity stays quantized, $σ_{\rm T\uparrow}(Ω\to 0)=σ_{\rm T\downarrow}(Ω\to 0)=e^2/h$. These results establish the Haldane-Hubbard model as a minimal correlated platform for odd-parity altermagnetic topology.

cond-mat.str-el↗

arXiv2026

Spin-orbit-enabled Fermi-surface splitting in noncollinear antiferromagnetic SmBi

Spin-split electronic structures in compensated antiferromagnets are commonly sought in the nonrelativistic limit, where magnetic order lifts spin degeneracy without spin-orbit coupling (SOC). Whether SOC can instead be the indispensable symmetry-breaking ingredient remains largely unexplored. Here we combine quantum oscillations detected by ultrahigh-sensitivity ac magnetostriction, magnetic-symmetry analysis and first-principles calculations to resolve the bulk Fermi-surface evolution of SmBi across two successive antiferromagnetic (AFM) transitions. New oscillation branches emerge below TN and undergo a further reconstruction below T*, whereas isostructural SmSb shows no comparable change. For the candidate noncollinear orders of SmBi, breaking global parity-time symmetry is insufficient in the nonrelativistic limit because residual spin-space symmetries protect twofold band degeneracy; conversely, SOC alone cannot lift the degeneracy of the centrosymmetric paramagnetic (PM) phase. Only the coexistence of noncollinear order and SOC locks spin to the lattice and removes the residual protection. SmBi therefore realizes a cooperative, relativistic route to spin-split Fermi surfaces, broadening unconventional magnetism beyond systems whose splitting is already present in the nonrelativistic limit.

cond-mat.mtrl-sci↗

arXiv2026

Altermagnetism in quasicrystals

Altermagnets are a recently discovered class of magnetic materials that combine a collinear, zero-magnetization spin structure, characteristic of antiferromagnets, with spin-split electronic bands, a hallmark of ferromagnets. This unique behavior arises from the breaking of combined time-reversal and spatial symmetries (such as inversion or lattice translation), which are preserved in conventional antiferromagnets. To date, research has mainly focused on altermagnetic phases in periodic crystals, where the order is linked to rotational symmetries compatible with translational periodicity. In this Letter, we demonstrate that quasicrystals, which possess rotational symmetries incompatible with periodicity, can host exotic altermagnetic orders. Using symmetry analysis and self-consistent mean-field theory, we predict stable $g$-wave and $i$-wave altermagnetism in octagonal and dodecagonal quasicrystals, respectively. These phases are characterized by global $C_8 T$ and $C_{12} T$ symmetries and exhibit anisotropic spin-splittings in their spectral functions and spin conductance, with characteristic eight- and twelve-fold nodal structures that establish a theoretical framework for identifying these phases in future experiments. Our findings establish quasicrystals as a versatile platform for realizing unconventional altermagnetic orders beyond the constraints of periodicity.

cond-mat.mes-hall↗

arXiv2026

Hybrid-order topology in two-dimensional nonsymmorphic antiferromagnets

We theoretically demonstrate hybrid-order topology in a two-dimensional nonsymmorphic antiferromagnet. Utilizing a generic antiferromagnetic Dirac model with a symmetry-allowed, momentum-dependent spin-density-wave (SDW) mass, we show that a single bulk insulating phase exhibits distinct topological boundary manifestations governed solely by the termination geometry. For screw-compatible edges, nonsymmorphic screw symmetry protects gapless first-order edge states. In contrast, for a $45^\circ$ diamond-shaped termination, the screw symmetry is broken at the boundary, resulting in gapped edges. However, the finite geometry still preserves magnetic mirror symmetries $\mathcal{M}_x\mathcal{T}$ and $\mathcal{M}_y\mathcal{T}$, which enforce an alternating pattern of edge masses, thereby binding zero-dimensional corner states. This second-order phase is characterized by a quantized quadrupole moment, with corner states pinned to zero energy by the chiral symmetry. We further demonstrate that explicit lattice perturbations can selectively gap the first-order edge modes while robustly preserving the corner states. Our work establishes a symmetry-based route to a termination-controlled duality between first- and second-order topology in magnetic nonsymmorphic systems.

cond-mat.mes-hall↗

arXiv2026

Engineering Helical Superconductors with Multiple Majorana Kramers Pairs via Higher-Order Rashba Spin-Orbit Coupling

The momentum dependence of Rashba spin-orbit coupling (RSOC) is a key ingredient for engineering topological superconductors (TSCs), yet research has overwhelmingly focused on its linear-in-momentum form. This focus has restricted time-reversal invariant TSCs to helical $p$-wave states, which are characterized by a $\mathbb{Z}_2$ topological invariant that permits at most a single Majorana Kramers pair at a given boundary. Their existence has also been tied to the stringent criterion of an odd number of Fermi surfaces (FSs). In this work, we establish higher-order RSOC as a powerful design principle to go beyond the $\mathbb{Z}_2$ classification and the odd-FS criterion. We demonstrate that a bilayer system with a pure cubic RSOC and an intrinsic odd-parity pairing on a single FS yields a rare 2D helical $f$-wave TSC. This state is characterized by a large mirror Chern number (MCN) of ${\cal N}_{\text{M}}=3$ and hosts three Kramers pairs of Majorana edge modes. Remarkably, the interplay of linear and cubic RSOCs in this bilayer can generate a helical hybrid $p+f$-wave TSC with an even larger MCN of ${\cal N}_{\text{M}}=4$ from a normal state with two FSs, thereby circumventing the conventional odd-FS criterion. Our work establishes higher-order RSOC as a "topology multiplier" for realizing TSCs with multiple Majorana Kramers channels, fundamentally reshapes the criteria for helical TSCs, and holds immediate relevance for tunable platforms like oxide heterostructures.

cond-mat.supr-con↗

arXiv2026

Floquet second-order topological insulator in strained graphene

Graphene provides a canonical setting for Floquet band engineering, where circularly polarized light can dynamically open topological gaps at Dirac points and generate nonequilibrium Hall responses. Here we show that uniaxial strain and off-resonant circularly polarized light with tunable incidence angle enable a controllable route to Floquet higher-order topology in graphene. Using a strained honeycomb tight-binding model with Peierls coupling and a high-frequency expansion for the effective Floquet Hamiltonian, we find that strain drives the Dirac cones toward the Dirac-merging (semi-Dirac) critical regime, where the light-induced mass becomes strongly anisotropic. For oblique incidence, the projected drive is effectively elliptically polarized and, in combination with strain, stabilizes a phase with gapped edges but robust in-gap corner modes in finite geometries, realizing a Floquet second-order topological insulator. We characterize the phase diagram via the Chern number and a crystalline-symmetry-quantized polarization invariant. Finally, first-principles-informed tight-binding calculations corroborate the predicted topological evolution in strained graphene nanostructures. Our results identify driven strained graphene as a realistic and tunable platform for realizing and diagnosing Floquet higher-order topological phases.

cond-mat.mes-hall↗

arXiv2026

Chiral Superconductivity in Periodically Driven Altermagnet/Superconductor Heterostructures

The interplay between magnetism and superconductivity provides a fertile ground for engineering exotic topological phases, while dynamical control via periodic driving offers a unique avenue to access quantum states that are inaccessible in static equilibrium. Here, we propose a strategy to achieve the Floquet chiral topological superconductivity in an altermagnet-superconductor heterostructure driven by elliptically polarized light. We show that for $s$-wave pairing, the system undergoes a transition from a trivial to a chiral topological superconducting phase. More strikingly, with the introduction of mixed $s+d$-wave pairing, we find that the system can access Floquet chiral topological superconducting phases with highly tunable Chern numbers up to N=4. These exotic phases are attributed to the intertwining of altermagnetism, superconducting pairing, and the periodic driving field. Our work establishes the light-driven altermagnetic heterostructure as a versatile platform for exploring and manipulating high-Chern-number chiral topological superconductivity.

cond-mat.supr-con↗

arXiv2026

The odd-parity altermagnetism: A spin group study

Following recent intensive studies on altermagnetism(ALM) characterized by non-relativistic even-parity spin splitting, realizing unconventional odd-parity magnetism has also attracted increasing interest. Here, using symmetry arguments based on spin-group analyses, we elucidate sufficient conditions for the emergence of odd-parity spin splitting in collinear antiferromagnetic systems, which is further established as the standard odd-parity ALM. It is derived that the odd-parity ALM arises from the following criteria: (i)the breaking nonmagnetic time reversal symmetry(TRS), i.e., the breaking real-space TRS; (ii)the long-range collinear compensated magnetism; (iii)the symmetry $[C_{2}||\bar{E}]$ or $[C_{2}||M]$ connecting opposite-spin sublattices, where $C_{2}$, $\bar{E}$, and $M$ respectively represent a $180^{\circ}$ rotation around the axis perpendicular to spins, the inversion, and the mirror reflection separating opposite-spin sublattices, directly reflecting the high-order harmonic($l\ge3$) and the $p$-wave($l=1$) odd-parity ALM, respectively. Moreover, we utilize the well-known Haldane-Hubbard model to identify odd-parity spin splitting in the collinear ALM ground state, where (i)the nonmagnetic TRS is broken by opposite sublattice currents coming from the Haldane hopping; (ii)the symmetry $[C_{2}||\bar{E}]$ is ensured because the currents flowing on opposite-spin sublattices are reversed.

cond-mat.str-el↗

arXiv2026

Light-Tunable Giant Anomalous Hall Effect in the Flat-Band Magnetic Weyl Semimetal $\mathrm{AlFe_2O_4}$

Achieving a giant anomalous Hall effect (AHE) and enabling its effective tuning are fundamental goals for topological spintronics. Magnetic Weyl semimetals hosting flat bands offer a promising route to maximize the AHE. However, while theoretical models are well-established, realistic material candidates remain scarce. Since the intrinsic anomalous Hall conductivity (AHC) is topologically dictated by the momentum separation ($κ$) between Weyl nodes, actively manipulating remains a key challenge. Here, through comprehensive first-principles calculations, we establish the inverse spinel $\mathrm{AlFe_2O_4}$ as a realistic ferromagnetic half-metallic platform integrating three-dimensional flat bands and Weyl physics. Spin-orbit coupling induces a single pair of Weyl nodes, yielding a giant intrinsic AHC of $398\ \mathrm{S}\cdot\mathrm{cm}^{-1}$. By constructing a symmetry-constrained tight-binding model, we uncover a deterministic relationship between microscopic electronic couplings and the macroscopic AHE. Exploiting this via Floquet engineering with circularly polarized light, we demonstrate that the effective couplings are dynamically suppressed. This optical modulation controllably enlarges $κ$, shortens the topological Fermi arcs, and drives a dramatic, quantitative suppression of the AHC, providing a practical blueprint for ultrafast, light-controlled topological transport.

cond-mat.mtrl-sci↗

arXiv2026

Anomalous Hall Conductivity as an Effective Means of Tracking the Floquet Weyl Nodes in Quasi-One-Dimensional $β$-Bi$_4$I$_4$

While Floquet engineering offers a powerful paradigm for manipulating topological phases, particularly Floquet Weyl semimetals, establishing an experimentally feasible strategy for tracking the dynamic evolution of such states remains a significant challenge. Here, we propose that the anomalous Hall effect (AHE), as a sensitive, all-electrical probe, can be used to track Floquet Weyl nodes. Using first-principles calculations and symmetry analysis on the quasi-one-dimensional material $β$-Bi$_4$I$_4$, we demonstrate that circularly polarized light breaks time-reversal symmetry, driving the system from a trivial insulator into a Floquet Weyl semimetal phase characterized by a nonzero Berry curvature flux. Crucially, by continuously tuning the polarization phase $φ$ of the driving field, we show that the trajectory of the induced Weyl nodes is highly controllable, leading to their migration and eventual annihilation at high-symmetry points. We reveal that the anomalous Hall conductivity maps directly onto this topological evolution, serving as a definitive fingerprint for the generation and dynamics of Weyl nodes.

cond-mat.mtrl-sci↗

arXiv2026

Light-induced Odd-parity Magnetism in Conventional Collinear Antiferromagnets

Recent studies have drawn growing attention on non-relativistic odd-parity magnetism in the wake of altermagnets. Nevertheless, odd-parity spin splitting is often believed to appear in non-collinear magnetic configurations. Here, using symmetry arguments and effective model analysis, we show that Floquet engineering offers a universal strategy for achieving odd-parity magnetism in two-dimensional (2D) collinear antiferromagnets under irradiation of periodic driving light fields such as circularly polarized light, elliptically polarized light, and bicircular light. A comprehensive classification of potential candidates for collinear monolayer or bilayer antiferromagnets is established. Strikingly, the light-induced odd-parity spin splitting can be flexibly controlled by adjusting the crystalline symmetry or the polarization state of incident light, enabling the reversal or conversion of spin-splitting. By combining first-principles calculations and Floquet theorem, we present illustrative examples of 2D collinear antiferromagnetic (AFM) materials to verify the light-induced odd-parity magnetism. Our work not only offers a powerful approach for uniquely achieving odd-parity spin-splitting with high tunability, but also expands the potential of Floquet engineering in designing unconventional compensated magnetism.

cond-mat.mtrl-sci↗

arXiv2026

Tunable intersublattice exchange coupling drives magnetic evolution in Mn$_{3+x}$Ga$_{1-x}$C ($0 \le x \le 0.60$)

We investigate the magnetic and transport evolution in Mn$_{3+x}$Ga$_{1-x}$C ($0 \le x \le 0.60$), where Mn substitution at corner Ga sites induces lattice contraction and suppresses the antiferromagnetic order of Mn$_3$GaC. As $x$ increases, the magnetic ground state of the system undergoes a sequential transition from an antiferromagnetic state, via a canted ferrimagnetic state, to a robust ferrimagnetic state, accompanied by a surge in the magnetic ordering temperature. Saturation magnetic moments reaches a maximum of 3.63~$μ_{\mathrm{B}}$/f.u. at $x = 0.10$, whereas the topological Hall resistivity peaks at 1.47~$μΩ\cdot$cm for $x = 0.20$ before decreasing with further doping. First-principles calculations demonstrate a $\sim\!40^{\circ}$ canting of face-centered Mn moments at $x = 0.20$, signifying spin frustration, and an eventual antiparallel alignment of face-centered and corner-site Mn moments at higher $x$. These results reveal that intersublattice antiferromagnetic coupling governs the magnetic transformation and emergent transport phenomena, thus providing a microscopic foundation for designing high-ordering-temperature antiperovskites.

cond-mat.mtrl-sci↗

arXiv2025

Gyrotropic Magnetic Effect in Black Phosphorus Irradiated with Bicircular Light

The gyrotropic magnetic effect (GME), which emerges as the low-frequency limit of natural gyrotopy, is a fundamental property of Bloch electrons on the Fermi surface in materials lacking inversion symmetry. While Weyl semimetals were among the first systems predicted to host the GME, this effect has not yet been experimentally observed in these materials. Here, we theoretically propose a robust scheme to generate a significant GME in anisotropic nodal-line semimetals using Floquet engineering with bicircular light (BCL). We show that BCL irradiation can selectively break spatial and time-reversal symmetries, inducing a topological phase transition from a nodal-line semimetal to a Weyl semimetal with a minimal number of Weyl nodes. Crucially, the Weyl nodes with opposite chirality are separated in energy, a key requirement for a non-zero GME. Using first-principles calculations combined with Floquet theory, we identify compressed black phosphorus as an ideal material platform. The intrinsic anisotropy of black phosphorus amplifies the GME, resulting in a measurable gyrotropic current that is several orders of magnitude larger than that in previously proposed systems. Our work not only provides a concrete path toward the experimental realization of GME but also opens new avenues for exploring the interplay of light, symmetry, and topology in quantum materials.

cond-mat.mtrl-sci↗

arXiv2025

The spin Hall conductivity in the hole-doped bilayer Haldane-Hubbard model with odd-parity ALM

Spin current generated electrically is among the core phenomena of spintronics for driving high-performance spin device applications. Here, on the basis of systematic investigations for the hole doped single-layer Haldane-Hubbard(HH) model, we propose a new bilayer HH model to realize the compensated odd-parity spin splitting and the $T$-even spin Hall conductivity where the two layers are connected by the time reversal transformation. Our results show that the vanishing layer-dependent electric potential $V_{L}$ gives rise to odd-parity ALM protected by the combined symmetry $TM_{xy}$ with $T$ and $M_{xy}$ being the time reversal and mirror reflection perpendicular to $z$ axis, and the $T$-even spin Hall conductivity simultaneously. In addition, though the staggered magnetization within each layer is substantially impacted by the layer-dependent electric potential, small $V_{L}$'s only bring negligible changes to the net magnetization and the spin Hall conductivity, indicating that the alternating spin splitting in momentum space and the spin Hall conductivity are insusceptible to external elements. Most importantly, our work provides a general framework for the simultaneous realization of the compensated odd-parity spin splitting in momentum space and the spin Hall conductivity in collinear magnets, in terms of stacked multi-layer systems.

cond-mat.str-el↗

arXiv2025

Spin-Orbital Altermagnetism

Altermagnet is a newly discovered magnetic phase, characterized by non-relativistic spin-splitting that has been experimentally observed. Here, we introduce a framework dubbed {\it spin-orbital altermagnetism} to achieve spin-orbital textures in altermagnetic materials. We identify two distinct classes of spin-orbital altermagnetism: intrinsic and extrinsic. The intrinsic type emerges from symmetry-compensated magnetic orders with spontaneously broken parity-time symmetry, while the extrinsic type stems from translational-symmetry breaking between sublattices, as exemplified by the Jahn-Teller-driven structural phase transition. In addition to directly measuring the spin-orbital texture, we propose spin conductivity and spin-resolved orbital polarization as effective methods for detecting these altermagnets. Additionally, a symmetry-breaking mechanism induces weak spin magnetization, further revealing the peculiar feature of spin-orbital altermagnetism. We also utilize the staggered susceptibility to illustrate a potential realization of this phase in a two-orbital interacting system. Our work provides a new platform to explore spin-orbital locked physics, extending the materials classes that may display complex spin textures from the standard $4d-5d$ compounds to $3d$ compounds.

cond-mat.str-el↗

arXiv2025

Quantum Spin Hall Effect with Extended Topologically Protected Features in Altermangetic Multilayers

Conventional topological classification theory dictates that time-reversal symmetry confines the quantum spin Hall (QSH) effect to a $\mathbb{Z}_2$ classification, permitting only a single pair of gapless helical edge states. Here, we utilize the recently discovered altermagnetism to circumvent this fundamental constraint. We demonstrate the realization of a unique QSH phase possessing multiple pairs of gapless helical edge states in altermagnetic multilayers. This exotic QSH phase, characterized by a mirror-spin Chern number, emerges from the interplay of spin-orbit coupling and $d$-wave altermagnetic ordering. Moreover, using first-principles calculations, we identify altermagnetic Fe$_2$Se$_2$O multilayers as promising material candidates, in which the number of gapless helical edge states scales linearly with the number of layers, leading to a correspondingly large, exactly quantized, and experimentally accessible spin-Hall conductance. Our findings unveil a new mechanism for stabilizing multiple pairs of gapless helical edge states, significantly expanding the scope of QSH effects, and provide a blueprint for utilizing altermagnetism to engineer desired topological phases.

cond-mat.mes-hall↗

arXiv2025

Floquet control of topological phases and Hall effects in Z2 nodal line semimetals

Dynamic control of topological properties in materials is central to modern condensed matter physics, and Floquet engineering, utilizing periodic light fields, provides a promising avenue. Here, we use Floquet theory to theoretically study the topological response of a Z2 nodal line semimetal (NLSM) when driven by circularly polarized light (CPL). We demonstrate that the direction of CPL irradiation critically dictates the resulting topological phase transitions. Specifically, when light is incident perpendicular to the nodal line plane, increasing the light amplitude induces two successive topological phase transitions: first, from the Z2 NLSM to a vortex NLSM, a rare and intriguing topological state; and second, a transition from the vortex NLSM to a semimetal with a pair of Weyl points (WPs). In stark contrast, irradiation along other directions directly transforms the Z2 nodal line into a pair of WPs. We further investigate the transport properties of the Floquet Z2 NLSM, focusing on the anomalous and planar Hall effects. The anomalous Hall effect exhibits a direction-dependent amplitude variation, deviating from conventional two-band NLSM behavior. Importantly, we reveal a significant and tunable planar Hall effect, a phenomenon largely unexplored in Floquet topological materials, which is highly sensitive to both light amplitude and direction. Our findings not only present a novel route to realize the vortex NLSM, but also establish an efficient way to control Hall transport phenomena in Z2 NLSMs.

cond-mat.str-el↗