arXiv subjects

Ya-Jie Wu

Publications and source records attributed to Ya-Jie Wu.

At least 19 recordsLinked to original sources

arXiv2025

Quantum spin-tensor Hall effect protected by pseudo time-reversal symmetry

The celebrated family of the Hall effect plays a fundamental role in modern physics. Starting from the anomalous Hall effect (AHE) and the quantum AHE (QAHE) with broken time-reversal symmetry (TRS) to their spinful generalizations, including spin Hall effect (SHE) and quantum SHE (QSHE) protected by TRS, they reveal rich transport and topological phenomena. However, in larger-spin $S$ ($S>1/2$) systems, besides charge current and spin current, there arise higher-rank spin-tensor currents. Recent work has uncovered an interesting spin-tensor Hall effect with spin-tensor currents in these larger-spin systems. Taking a step further, this work discovers a new class of topological states of matter dubbed \textit{quantum spin-tensor Hall} (QSTH) insulators with broken TRS, and their nontrivial topology is protected by a unique \textit{pseudo-TRS}. Most strikingly, QSTH insulators exhibit a quantized rank-2 spin-tensor Hall conductivity, whereas both charge (rank-0) and spin (rank-1) conductivities vanish. We also fully characterize their topological properties and highlight the physical interpretations via the underlying connections to QSHE. Our work enriches the family of the famous Hall effects and sheds light on the intriguing topological state of matter in larger-spin systems. It further offers new avenues toward spin-tensor-tronics and low-power atomtronics.

cond-mat.mes-hall↗

arXiv2024

Cancellation theorem breaking and resonant spin-tensor Hall conductivity in higher-rank spin-tensor Hall effects

With recent advances in simulating quantum phenomena in cold atoms, the higher-rank spin tensor Hall effect was discovered in larger spin systems with spin-tensor-momentum coupling, which is an extension of the celebrated spin Hall effects in larger spins. Previously, it has been proposed that a 2D electron gas with Rashba spin-orbit coupling can generate dissipationless transverse spin current, namely the spin Hall effect. However, later work showed that the spin current is canceled by vertex correction, which was subsequently proven by a cancellation theorem that does not depend on any assumptions related to the scattering mechanism, the strength of spin-orbit coupling, or the Fermi energy. While the recent proposal demonstrates a universal intrinsic spin-tensor Hall conductivity, it is unclear if it vanishes similarly to the spin Hall effect. In this work, we address this critical problem and show that the rank-2 spin-tensor current can be divergent by considering the contributions of both interbranch and intrabranch transitions, which resembles the quantum Hall effect in some sense. So the \textit{universal} spin-tensor Hall effect can not be observed in a system with finite size. However, we further show that there is an \textit{observable non-zero} resonance of spin-tensor Hall conductivity as the Landau levels cross under the magnetic field. Our work reveals interesting conductivity properties of larger-spin systems and will provide valuable guidance for experimental explorations of higher-rank spin-tensor Hall effects, as well as their potential device applications.

cond-mat.mes-hall↗

arXiv2023

Bogoliubov Corner Excitations in Conventional $s$-Wave Superfluids

Higher-order topological superconductors and superfluids have triggered a great deal of interest in recent years. While Majorana corner or hinge states have been studied intensively, whether superconductors and superfluids, being topological or trivial, host higher-order topological Bogoliubov excitations remains elusive. In this work, we propose that Bogoliubov corner excitations can be driven from a trivial conventional $s$-wave superfluid through mirror-symmetric local potentials. The topological Bogoliubov excited modes originate from the nontrivial Bogoliubov excitation bands. These modes are protected by mirror symmetry and robust against mirror-symmetric perturbations as long as the Bogoliubov energy gap remains open. Our work provides new insight into higher-order topological excitation states in superfluids and superconductors.

cond-mat.quant-gas↗

arXiv2022

Higher-order Topological Phases of Magnons in van der Waals Honeycomb Ferromagnets

We theoretically propose a second-order topological magnon insulator by stacking the van der Waals honeycomb ferromagnets with antiferromagnetic interlayer coupling. The system exhibits Z$_{2}$ topological phase, protected by pseudo-time-reversal symmetry (PTRS). An easy-plane anisotropy term breaks PTRS and destroys the topological phase. Nevertheless, it respects a magnetic two-fold rotational symmetry which protects a second-order topological phase with corner modes in bilayer and hinge modes along stacking direction. Moreover, an introduced staggered interlayer coupling establishes a Z$_{2}$$\times$Z topology, giving rise to gapped topological surface modes carrying non-zero Chern numbers. Consequently, chiral hinge modes propagate along the horizontal hinges in a cuboid geometry and are robust against disorders. Our work bridges the higher-order topology and magnons in van der Waals platforms, and could be used for constructing topological magnonic devices.

cond-mat.mes-hall↗

arXiv2022

Majorana corner states in an attractive quantum spin Hall insulator with opposite in-plane Zeeman energy at two sublattice sites

Higher-order topological superconductors and superfluids host lower-dimensional Majorana corner and hinge states since novel topology exhibitions on boundaries. While such topological nontrivial phases have been explored extensively, more possible schemes are necessary for engineering Majorana states. In this paper we propose Majorana corner states could be realized in a two-dimensional attractive quantum spin-Hall insulator with opposite in-plane Zeeman energy at two sublattice sites. The appropriate Zeeman field leads to the opposite Dirac mass for adjacent edges of a square sample, and naturally induce Majorana corner states. This topological phase can be characterized by Majorana edge polarizations, and it is robust against perturbations on random potentials as long as the edge gap remains open. Our work provides a new possibility to realize a second-order topological superfluid in two dimensions and engineer Majorana corner states.

cond-mat.mes-hall↗

arXiv2022

Higher-order topological corner states induced solely by onsite potentials with mirror symmetry

Higher-order topological insulators have triggered great interests because of exhibitions of non-trivial bulk topology on lower-dimensional boundaries like corners and hinges. While such interesting phases have been investigated in a plethora of systems by tuning staggered tunneling strength or manipulating existing topological phases, here we show that a higher-order topological phase can be driven solely by mirror-symmetric onsite potentials. We first introduce a simple chain model in one dimension that mimics the Su-Schrieffer-Heeger-like model. However, due to the lack of internal symmetries like chiral or particle-hole symmetry, the energies of the topological edge modes are not pinned at zero. Once the model is generalized to two dimensions, we observe the emergence of topological corner modes. These corner modes are intrinsic manifestation of non-trivial bulk band topology protected by mirror symmetry, and thus, they are robust against symmetry-preserved perturbations. Our study provides a concise proposal for realizing a class of higher-order topological insulators, which involves only tuning onsite energies. This can be easily accessible in experiments and provides a different playground for engineering topological corner modes.

cond-mat.mes-hall↗

arXiv2020

Majorana corner pairs in a two-dimensional $s$-wave cold atomic superfluid

We propose a method to prepare Majorana pairs at the corners of imprinted defects on a two-dimensional cold atom optical lattice with $s$-wave superfluid pairing. Different from previous proposals that manipulate the effective Dirac masses, our scheme relies on the sign flip of the spin-orbit coupling at the corners, which can be tuned in experiments by adjusting the angle of incident Raman lasers. The Majorana corner pairs are found to be located at the interface between two regimes with opposite spin orbit coupling strengths in an anticlockwise direction and are robust against certain symmetry-persevered perturbations. Our work provides a new way for implementing and manipulating Majorana pairs with existing cold-atom techniques.

cond-mat.quant-gas↗

arXiv2020

In-plane Zeeman field induced Majorana corner and hinge modes in an $s$-wave superconductor heterostructure

Second-order topological superconductors host Majorana corner and hingemodes in contrast to conventional edge and surface modes in two and three dimensions. However, the realization of such second-order corner modes usually demands unconventional superconducting pairing or complicated junctions or layered structures. Here we show that Majorana corner modes could be realized using a 2D quantum spin Hall insulator in proximity contact with an $s$-wave superconductor and subject to an in-plane Zeeman field. Beyond a critical value, the in-plane Zeeman field induces opposite effective Dirac masses between adjacent boundaries, leading to one Majorana mode at each corner. A similar paradigm also applies to 3D topological insulators with the emergence of Majorana hinge states. Avoiding complex superconductor pairing and material structure, our scheme provides an experimentally realistic platform for implementing Majorana corner and hinge states.

cond-mat.mes-hall↗

arXiv2020

Two-dimensional non-Hermitian topological phases induced by asymmetric hopping in a one-dimensional superlattice

Non-Hermitian systems can host topological states with novel topological invariants and bulk-edge correspondences that are distinct from conventional Hermitian systems. Here we show that two unique classes of non-Hermitian 2D topological phases, a 2$\mathbb{Z}$ non-Hermitian Chern insulator and a $\mathbb{Z}_{2}$ topological semimetal, can be realized by tuning staggered asymmetric hopping strengths in a 1D superlattice. These non-Hermitian topological phases support real edge modes due to robust $\mathcal{PT}$-symmetric-like spectra and can coexist in certain parameter regime. The proposed phases can be experimentally realized in photonic or atomic systems and may open an avenue for exploring novel classes of non-Hermitian topological phases with 1D superlattices.

cond-mat.mes-hall↗

arXiv2020

Wannier-type photonic higher-order topological corner states induced solely by gain and loss

Photonic crystals have provided a controllable platform to examine excitingly new topological states in open systems. In this work, we reveal photonic topological corner states in a photonic graphene with mirror-symmetrically patterned gain and loss. Such a nontrivial Wannier-type higher-order topological phase is achieved through solely tuning on-site gain/loss strengths, which leads to annihilation of the two valley Dirac cones at a time-reversal-symmetric point, as the gain and loss change the effective tunneling between adjacent sites. We find that the symmetry-protected photonic corner modes exhibit purely imaginary energies and the role of the Wannier center as the topological invariant is illustrated. For experimental considerations, we also examine the topological interface states near a domain wall. Our work introduces an interesting platform for non-Hermiticity-induced photonic higher-order topological insulators, which, with current experimental technologies, can be readily accessed.

cond-mat.mes-hall↗

arXiv2019

Non-Hermitian topological phase transitions for quantum spin Hall insulators

The interplay between non-Hermiticity and topology opens an exciting avenue for engineering novel topological matter with unprecedented properties. While previous studies have mainly focused on one-dimensional systems or Chern insulators, here we investigate topological phase transitions to/from quantum spin Hall (QSH) insulators driven by non-Hermiticity. We show that a trivial to QSH insulator phase transition can be induced by solely varying non-Hermitian terms, and there exists exceptional edge arcs in QSH phases. We establish two topological invariants for characterizing the non-Hermitian phase transitions: i) with time-reversal symmetry, the biorthogonal $\mathbb{Z}_2$ invariant based on non-Hermitian Wilson loops, and ii) without time-reversal symmetry, a biorthogonal spin Chern number through biorthogonal decompositions of the Bloch bundle of the occupied bands. These topological invariants can be applied to a wide class of non-Hermitian topological phases beyond Chern classes, and provides a powerful tool for exploring novel non-Hermitian topological matter and their device applications.

cond-mat.mes-hall↗

arXiv2019

Symmetry-protected localized states at defects in non-Hermitian systems

Understanding how local potentials affect system eigenmodes is crucial for experimental studies of nontrivial bulk topology. Recent studies have discovered many exotic and highly non-trivial topological states in non-Hermitian systems. As such, it would be interesting to see how non-Hermitian systems respond to local perturbations. In this work, we consider chiral and particle-hole -symmetric non-Hermitian systems on a bipartite lattice, including SSH model and photonic graphene, and find that a disordered local potential could induce bound states evolving from the bulk. When the local potential on a single site becomes infinite, which renders a lattice vacancy, chiral-symmetry-protected zero-energy mode and particle-hole symmetry-protected bound states with purely imaginary eigenvalues emerge near the vacancy. These modes are robust against any symmetry-preserved perturbations. Our work generalizes the symmetry-protected localized states to non-Hermitian systems.

cond-mat.dis-nn↗

arXiv2017

Fermi Arcs in Tilted Weyl Semimetals: Classification, Evolution and Transport Properties

The Weyl semimetal is a new quantum state of topological semimetal, of which topological surface states -- the Fermi arcs exist. In this paper, the Fermi arcs in Weyl semimetals are classified into two classes -- class-1 and class-2. Based on a tight-binding model, the evolution and transport properties of class-1/2 Fermi arcs are studied via the tilting strength of the bulk Weyl cones. The (residual) anomalous Hall conductivity of topological surface states is a physical consequence of class-1 Fermi arc and thus class-1 Fermi arc becomes a nontrivial topological property for hybrid or type-II Weyl semimetal. Therefore, this work provides an intuitive method to learn topological properties of Weyl semimetal.

cond-mat.mtrl-sci↗

arXiv2017

Phase shift formulas for baryon-baryon scattering in elongated boxes

We have established the relations between the baryon-baryon scattering phase shifts and the two-particle energy spectrum in the elongated box. We have studied the cases with both the periodic boundary condition and twisted boundary condition in the center of mass frame. The framework is also extended to the system of nonzero total momentum with periodic boundary condition in the moving frame. This will be helpful to extract the phase shifts in the continuum from lattice QCD data using asymmetric volumes.

nucl-th↗

arXiv2017

Weyl Bogoliubov excitations in Bose-Hubbard extension of Weyl semimetal

In this paper, a Bose-Hubbard extension of a Weyl semimetal is proposed that can be realized for ultracold atoms using laser assisted tunneling and Feshbach resonance technique in three dimensional optical lattices. The global phase diagram is obtained consisting of a superfluid phase and various Mott insulator phases by using Landau theory. The Bogoliubov excitation modes for the weakly interacting case have nontrivial properties (Weyl nodes, bosonic surface arc, etc.) analogs of those in Weyl semimetals of electronic systems, which are smoothly carried over to that of Bloch bands for the noninteracting case. The properties of the insulating phases for the strongly interacting case are explored by calculating both the quasiparticle and quasihole dispersion relation, which shows two quasiparticle spectra touch at Weyl nodes.

cond-mat.quant-gas↗

arXiv2016

Electronic transport of bilayer graphene with asymmetry line defects

In this paper, we study the quantum properties of a bilayer graphene with (asymmetry) line defects. The localized states are found around the line defects. Thus, the line defects on one certain layer of the bilayer graphene can lead to an electric transport channel. By adding a bias potential along the direction of the line defects, we calculate the electric conductivity of bilayer graphene with line defects using Landauer-Büttiker theory, and show that the channel affects the electric conductivity remarkably by comparing the results with those in a perfect bilayer graphene. This one-dimensional line electric channel has the potential to be applied in the nanotechnology engineering.

cond-mat.mes-hall↗

arXiv2015

Effects of Attractive correlation on Topological Flat-bands Model

In this paper, we study the effects of attractive correlation on the topological insulator ($TI$) with topological flat-bands using an extended attractive Kane-Mele-Hubbard model (KMHM). In the KMHM, we found a quantum phase transition from $TI$ to the superconductor ($SC$) state upon the increasing of the attractive Hubbard interaction $U$ at the mean field level. This type of $SC$ phase transition is different from the traditional $SC$ phase transition which develops from the gapless Fermi Liquid. Cooperon-type gapped excitations exist in the $TI$ side near this type of $SC$ phase transition.

cond-mat.str-el↗

arXiv2014

Topological Mid-gap States of px+ipy Topological Superconductor with Vortex superlattice

In this paper, the px+ipy topological superconductor with vortex superlattice is studied. We found that there exist mid-gap energy bands induced by the vortex superlattice and the mid-gap energy bands have nontrivial topological properties including the gapless edge states and non-zero winding number. An topological anisotropic tight-binding Majorana lattice model is proposed to describe the mid-gap states.

cond-mat.supr-con↗