arXiv subjects

Xiao-Jiao Wang

Publications and source records attributed to Xiao-Jiao Wang.

7 recordsLinked to original sources

arXiv2026

Light-Induced Even-Wave Spin Splittings in Nonmagnetic Centrosymmetric Systems with Spin-Orbit Coupling

Spin splitting underpins a vast range of spin-dependent phenomena. Traditionally, two primary mechanisms generate such splitting: relativistic spin-orbit coupling (SOC) and nonrelativistic magnetic exchange coupling (MEC). Governed by distinct symmetry constraints, they produce splittings of opposite parity -- odd for SOC and even for MEC -- a dichotomy that underpins the distinct spin physics of nonmagnetic and magnetic systems. In this work, we break this dichotomy by demonstrating the dynamic generation of even-parity spin splitting in centrosymmetric, nonmagnetic systems driven by circularly polarized light. We show that the symmetry of the induced splitting is controlled by the angular character of the underlying orbitals, enabling the realization of s-wave, d-wave, and g-wave spin-split band structures identical to those of ferromagnets and altermagnets. Furthermore, we find that these spin-split bands can naturally host a Chern insulator phase. We also discuss the associated spin and orbital magnetization. Our results establish a direct and previously unrecognized conceptual link between the two fundamental mechanisms of spin splitting.

cond-mat.mtrl-sci↗

arXiv2025

Intrinsic Second-Order Topological Superconductors with Tunable Majorana Zero Modes

Dirac semimetals, with their protected Dirac points, present an ideal platform for realizing intrinsic topological superconductivity. In this work, we investigate superconductivity in a two-dimensional, square-lattice nonsymmorphic Dirac semimetal. In the normal state near half-filling, the Fermi surface consists of two distinct pockets, each enclosing a Dirac point at a time-reversal invariant momentum ($\textbf{X}=(π,0)$ and $\textbf{Y}=(0,π)$). Considering an on-site repulsive and nearest-neighbor attractive interaction, we use self-consistent mean-field theory to determine the ground-state pairing symmetry. We find that an even-parity, spin-singlet $d_{x^{2}-y^{2}}$-wave pairing is favored as it gives rise to a fully gapped superconducting state. Since the pairing amplitude has opposite signs on the two Dirac Fermi pockets, the superconducting state is identified as a second-order topological superconductor. The hallmark of this topological phase is the emergence of Majorana zero modes at the system's boundaries. Notably, the positions of these Majorana modes are highly controllable and can be manipulated simply by tailoring the boundary sublattice terminations. Our results highlight the promise of nonsymmorphic Dirac semimetals for realizing and manipulating Majorana modes.

cond-mat.supr-con↗

arXiv2025

Coexistence of Chiral Majorana Edge States and Bogoliubov Fermi Surfaces in Two-Dimensional Nonsymmorphic Dirac Semimetal/Superconductor Heterostructures

Dirac semimetals are renowned for the host of singular symmetry-protected band degeneracies which can give rise to other exotic phases. In this work, we consider a two-dimensional Dirac semimetal stabilized by PT symmetry and nonsymmorphic symmetries. We find that an out-of-plane Zeeman field can lift the Dirac points and transform the system into a Chern insulator with chiral edge states. By placing the nonsymmorphic Dirac semimetal in proximity to an s-wave superconductor, we uncover that chiral topological superconductors with large Chern numbers can be achieved. In addition, we find that topologically-protected Bogoliubov Fermi surface can also emerge in this system, due to the coexistence of inversion symmetry and particle-hole symmetry. Notably, we find that the chiral Majorana edge state persists even when the Chern number becomes ill-defined due to the appearance of Bogoliubov Fermi surfaces. The impact of these Bogoliubov Fermi surfaces on the thermal Hall effects is also investigated. Our study not only identifies a class of materials capable of realizing topological Bogoliubov Fermi surfaces through conventional s-wave superconductivity, but also uncovers an exotic phase where chiral Majorana edge states and Bogoliubov Fermi surfaces coexist.

cond-mat.mes-hall↗

arXiv2025

Topological superconductivity in two-dimensional $π$-junction Dirac semimetals

Odd-parity pairings offer a natural pathway for realizing topological superconductivity. When two identical even-parity superconductors form a $π$-junction, the metallic material sandwiched between them experiences an effective odd-parity pairing, facilitating the emergence of topological superconductivity in the intermediate region. In this work, we consider the intermediate material to be a two-dimensional spin-orbit-coupled Dirac semimetal. When the two superconductors are conventional s-wave superconductors, we find that a helical topological superconductor can be realized. This phase is characterized by the presence of a pair of helical Majorana edge states. Interestingly, when the superconductors are $s_{\pm}$-wave superconductors, we observe not only the helical topological superconductor but also an unconventional topological superconductor. The latter is distinguished by the existence of two pairs of helical Majorana edge states, despite the fact that the global topological invariants for this system take on trivial values. By further applying an in-plane magnetic field, we demonstrate that second-order topological superconducting phases can be achieved. These phases host isolated Majorana corner modes as well as twofold Majorana corner modes. Our findings reveal that two-dimensional $π$-junction Dirac semimetals can support a rich variety of topological superconducting phases, offering a versatile platform for exploring exotic topological phenomena.

cond-mat.supr-con↗

arXiv2024

Boundary Flat Bands with Topological Spin Textures Protected by Sub-chiral Symmetry

Chiral symmetry plays an indispensable role in topological classifications as well as in the understanding of the origin of bulk or boundary flat bands. The conventional definition of chiral symmetry refers to the existence of a constant unitary matrix anticommuting with the Hamiltonian. As a constant unitary matrix has constant eigenvectors, boundary flat bands enforced by chiral symmetry, which share the same eigenvectors with the chiral symmetry operator, are dictated to carry fixed (pseudo)spin polarizations and be featureless in quantum geometry. In this work, we generalize the chiral symmetry and introduce a concept termed sub-chiral symmetry. Unlike the conventional chiral symmetry operator defined as constant matrix, the sub-chiral symmetry operator depends on partial components of the momentum vector, so as its eigenvectors. We show that topological gapped or gapless systems without chiral symmetry but with sub-chiral symmetry can support boundary flat bands, which exhibit topological spin textures and quantized Berry phases. We expect that such intriguing boundary flat bands could give rise to a variety of exotic physics in the presence of interactions or disorders.

cond-mat.mtrl-sci↗

arXiv2024

Berry-dipole Semimetals

We introduce ''Berry-dipole semimetals'', whose band degeneracies are characterized by quantized Berry dipoles. Through a two-band model constructed by Hopf map, we reveal that the Berry-dipole semimetals display a multitude of salient properties distinct from other topological semimetals. On the boundary, we find that the first-order Berry-dipole semimetal harbors anomalous paired Fermi arcs with the same spin polarization, even though the layer Chern number is zero, and the second-order Berry-dipole semimetal hosts dispersionless hinge arcs. In the bulk, we find that the low-energy Berry-dipole Hamiltonian near the band node has a quadratic energy dispersion and peculiar Berry curvature, which give rise to rather unique characteristics in the intrinsic anomalous Hall effect, orbital magnetization and Landau levels. Our study shows that Berry-dipole semimetals are a class of topological gapless phases supporting rich intriguing physics.

cond-mat.mes-hall↗

arXiv2024

Anomalous Linear and Quadratic Nodeless Surface Dirac Cones in Three-Dimensional Dirac Semimetals

Surface Dirac cones in three-dimensional topological insulators have generated tremendous and enduring interest for almost two decades owing to hosting a multitude of exotic properties. In this work, we unveil the existence of two types of anomalous surface Dirac cones in three-dimensional Dirac semimetals. These surface Dirac cones are located at the surfaces perpendicular to the rotation symmetry axis, and are found to display a number of features remarkably different from that in topological insulators. The most prominent one is the absence of singular Dirac node. In addition, the spin textures of these nodeless surface Dirac cones are found to exhibit a unique two-phase-angle dependence, leading to the presence of two different winding numbers in the orbital-resolved spin textures, which is rather different from the well-known spin-momentum locking in topological insulators. Despite the absence of Dirac node, we find that the two types of surface Dirac cones are also characterized by quantized $π$ Berry phases, even though one of them takes a quadratic dispersion. In the presence of time-reversal-symmetry-breaking fields, we find that the responses of the surface and bulk Dirac cones display an interesting bulk-surface correspondence. The uncovering of these nodeless surface Dirac cones broadens our understanding of the topological surface states and bulk-boundary correspondence in Dirac semimetals, and also lays down the basis for studying unconventional Dirac physics.

cond-mat.mtrl-sci↗