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Introduction

quantum transport and topological states in condensed materials

**Skills and Expertise**

## Publications

Publications (186)

The static topological fractional charge (TFC) in condensed matter systems is related to the band topology and thus has potential applications in topological quantum computation. However, the experimental measurement of these TFCs in electronic systems is quite challenging. We propose an electronic transport measurement scheme in which both the cha...

We study the characterization of the non-Hermitian skin effect (NHSE) in non-Hermitian systems with on-site disorders. We extend the applications of generalized Brillouin zone (GBZ) theory to these systems. By proposing a modified GBZ theory, we give a faithful description of the NHSE. For applications, we obtain a unified β for system with long-ra...

The nontrivial band topology can influence the Hofstadter spectrum. We investigate the Hofstadter spectrum for various models of Chern insulators under a rational flux $\frac{\phi_{0}}{q}$, here $\phi_{0}=\frac{h}{e}$ and $q$ being an integer. We find two major features. First, the number of splitting subbands is $|q-C|$ with Chern number $C$. Seco...

Energy dissipation is of fundamental interest and crucial importance in quantum systems. However, whether energy dissipation can emerge inside topological systems remains a question, especially when charge transport is topologically protected and quantized. As a hallmark, we propose a microscopic picture that illustrates energy dissipation in the q...

Fractional quantization can emerge in non-correlated systems due to the parity anomaly, while its condensed matter realization is a challenging problem. We propose that in axion insulators (AIs), parity anomaly manifests a unique fractional boundary excitation: the half-quantized helical hinge currents. These helical hinge currents microscopically...

The bulk-boundary correspondence (BBC) refers to the consistency between eigenvalues calculated under open and periodic boundary conditions. This consistency can be destroyed in systems with non-Hermitian skin effect (NHSE). In spite of the great success of the generalized Brillouin zone (GBZ) theory in clean non-Hermitian systems, the applicabilit...

We propose that the topological Anderson insulator (TAI) can be realized by introducing special disorder into a graphene with a modified Kane-Mele model. The disorder recovers symmetry under statistical averaging, which turns a trivial insulator into a topologically nontrivial insulator. When graphene is subjected to nonmagnetic adatoms in one subl...

The second harmonic generation (SHG) effect is a powerful tool for characterizing the magnetic structures of materials. Bridging the connection between the SHG effect and the symmetries of magnetic materials has been at the frontier of fundamental research in condensed matter physics. The construction of a complete and exclusive classification of S...

We study the quantized charge pumping of higher-order topological insulators (HOTIs) with edge-corner correspondences based on the combination of the rotation of in-plane magnetic field and the quantum spin Hall effect. The picture of a specific charge pumping process is uncovered with the help of the nonequilibrium Green's function method. Signifi...

The static topological fractional charge (TFC) in condensed matter systems is related to the band topology and thus has potential applications in topological quantum computation. However, the experimental measurement of these TFCs in electronic systems is quite challenging. We propose an electronic transport measurement scheme that both the charge...

We study the characterization of the non-Hermitian skin effect (NHSE) in non-Hermitian systems with on-site disorder. We extend the application of generalized-Brillouin-zone (GBZ) theory to these systems. By proposing a modified GBZ theory, we give a faithfully description of the NHSE. For applications, we obtain a unified $\beta$ for system with l...

Surface electrons in axion insulators are endowed with a topological layer degree of freedom followed by exotic transport phenomena, e.g., the layer Hall effect [Gao et al., Nature 595, 521 (2021)]. Here, we propose that such a layer degree of freedom can be manipulated in a dissipationless way based on the antiferromagnetic $\rm{MnBi_2Te_4}$ with...

We study the quantized charge pumping of higher-order topological insulators (HOTIs) with edge-corner correspondences based on the combination of the rotation of in-plane magnetic field and the quantum spin Hall effect. A picture of a specific charge pumping process is uncovered with the help of the non-equilibrium Green's function method. Signific...

Spontaneous polarization and bulk photovoltaic effect (BPVE) are two concomitant physical properties in ferroelectric materials. The flipping of ferroelectric order usually accompanies the switching of BPVE in all directions because both of them are reversed under the inversion symmetry. In this study, we report the non-synchronous BPVE in two-dime...

By incorporating the orbital magnetic moment, we investigate the magneto-optical transport of Weyl semimetals within a semiclassical approximation. In the linear or nonlinear response regime, an analytic expression for the magnetoconductivity is obtained, where a new term due to the orbital magnetic moment is added, and leads to a partial cancellat...

We propose that half-quantized helical hinge currents manifest as the fingerprint of the axion in-sulator (AI). These helical hinge currents microscopically originate from the lateral Goos-Hänchen (GH) shift of massless side-surface Dirac electrons that are totally reflected from the hinges. Meanwhile , due to the presence of the massive top and bo...

Spin superconductor (SSC) is an exciton condensate state where the spin-triplet exciton superfluidity is charge neutral while spin 2(ℏ/2). In analogy to the Majorana zero mode (MZM) in topological superconductors, the interplay between SSC and band topology will also give rise to a specific kind of topological bound state obeying non-Abelian braidi...

Motivated by the recent experiments that reported the discovery of vortex Majorana bound states (vMBSs) in iron-based superconductors, we establish a portable scheme to unveil the non-Abelian statistics of vMBSs using normal fermionic modes. The non-Abelian statistics of vMBSs are characterized by the charge flip signal of the fermions that can be...

Spontaneous polarization and bulk photovoltaic effect (BPVE) are two concomitant physical properties in ferroelectric materials. The flipping of ferroelectric order usually accompanies with the switching of BPVE as both of them are reversed under the inversion symmetry. In this study, we report the distinctive BPVE characters in two-dimensional (2D...

The consistency between eigenvalues calculated under open and periodic boundary conditions, named as {\it bulk-bulk correspondence} ($\mathcal{BBC}$), can be destroyed in systems with non-Hermitian skin effect (NHSE). In spite of the great success of the generalized Brillouin zone (GBZ) theory in clean non-Hermitian systems, the applicability of GB...

In most cases, to observe quantized Hall plateaus, an external magnetic field is applied in intrinsic magnetic topological insulators MnBi2Te4. Nevertheless, whether the nonzero Chern number (C≠0) phase is a quantum anomalous Hall (QAH) state, or a quantum Hall (QH) state, or a mixing state of both is still a puzzle, especially for the recently obs...

Recent discovered two-dimensional (2D) antiferromagnetic (AFM) van der Waals quantum materials have attracted increasing interest due to the emergent exotic physical phenomena. The spintronic properties utilizing the intrinsic AFM state in 2D antiferromagnets, however, have been rarely found. Here we show that the spin photogalvanic effect (SPGE),...

We study the construction of programable integrated circuits with the help of disordered Chern insulators. Specifically, the schemes for low dissipation logic devices and connecting wires are proposed. We use the external-gate-induced step voltage to construct spatially adjustable channels, where these channels take the place of the conventional wi...

Recently, a new class of second-order topological insulators (SOTIs) characterized by an electronic dipole has been theoretically introduced and proposed to host topological corner states. As a novel topological state, it has been attracting great interest and experimentally realized in artificial systems of various fields of physics based on multi...

We propose a general and tunable platform to realize high-density arrays of quantum spin-valley Hall kink (QSVHK) states with spin-valley-momentum locking based on a two-dimensional hexagonal topological insulator. Through the analysis of Berry curvature and topological charge, the QSVHK states are found to be topologically protected by the valley-...

Recently, a new class of second-order topological insulators (SOTIs) characterized by an electronic dipole has been theoretically introduced and proposed to host topological corner states. As a novel topological state, it has been attracting great interest and experimentally realized in artificial systems of various fields of physics based on multi...

Spin superconductor (SSC) is an exciton condensate state where the spin-triplet exciton superfluidity is charge neutral while spin $2(\hbar/2)$. In analogy to the Majorana zero mode (MZM) in topological superconductors, the interplay between SSC and band topology will also give rise to a specific kind of topological boundary state obeying non-Abeli...

We study the construction of programable integrated circuits with the help of disordered Chern insulators (CIs) in this letter. Specifically, the schemes for low dissipation logic devices and connecting wires are proposed. We use the external-gate-induced step voltage to construct spatially adjustable channels, where these channels take the place o...

In most cases, to observe quantized Hall plateaux, an external magnetic field is applied in intrinsic magnetic topological insulators $\mathrm{MnBi_2Te_4}$. Nevertheless, whether the nonzero Chern number ($C\neq 0$) phase is a quantum anomalous Hall (QAH) state, or a quantum Hall (QH) state, or a mixing state of both is still a puzzle, especially f...

We study the disorder-induced phase transition of higher-order Weyl semimetals (HOWSMs) and the fate of the topological features of disordered HOWSMs. We obtain a global phase diagram of HOWSMs utilizing the scaling theory of Anderson localization. Specifically, a phase transition from the Weyl semimetal (WSM) to the HOWSM is obtained, distinguishi...

Due to the unique band structure, graphene exhibits a number of exotic electronic properties that have not been observed in other materials. Among them, it has been demonstrated that there exist the one-dimensional valley-polarized topological kink states localized in the vicinity of the domain wall of graphene systems, where a bulk energy gap open...

We study the characterization and realization of higher-order topological Anderson insulator (HOTAI) in non-Hermitian systems, where the non-Hermitian mechanism ensures extra symmetries as well as gain and loss disorder. We illuminate that the quadrupole moment Qxy can be used as the real space topological invariant of non-Hermitian higher-order to...

The Magnus Hall effect (MHE) is a new type of linear-response Hall effect, recently proposed to appear in two-dimensional (2D) nonmagnetic systems at zero magnetic field in the ballistic limit. The MHE arises from a self-rotating Bloch electron moving under a gradient-electrostatic potential, analogous to the Magnus effect in the macrocosm. Unfortu...

Motivated by the recent experiments that reported the discovery of vortex Majorana bound states (vMBSs) in iron-based superconductors, we establish a portable scheme to unveil the non-Abelian statistics of vMBSs using normal fermionic modes. The unique non-Abelian statistics of vMBSs is characterized by the charge flip signal of the fermions that c...

Recently, the search for an axion insulator state in the ferromagnetic-3D topological insulator (TI) heterostructure and MnBi2Te4 has attracted intense interest. However, its detection remains difficult in experiments. We systematically investigate the disorder-induced phase transition of the axion insulator state in a 3D TI with antiparallel magne...

We study the characterization and realization of higher-order topological Anderson insulator (HOTAI) in non-Hermitian systems, where the non-Hermitian mechanism ensures extra symmetries as well as gain and loss disorder.We illuminate that the quadrupole moment $Q_{xy}$ can be used as the real space topological invariant of non-Hermitian higher-orde...

In this paper, we study an Anderson-localization-induced quantized transport in disordered Chern insulators (CIs). By investigating the disordered CIs with a step potential, we find that the chiral interface states emerge along the interfaces of the step potential, and the energy range for such quantized transport can be manipulated through the pot...

We propose a general and tunable platform to realize high-density arrays of quantum spin-valley Hall kink (QSVHK) states with spin-valley-momentum locking based on a two-dimensional hexagonal topological insulator. Through the analysis of Berry curvature and topological charge, the QSVHK states are found to be topologically protected by the valley-...

In analogy to real magnetic field, the pseudo-magnetic field (PMF) induced by inhomogeneous strain can also form the Landau levels and edge states. In this paper, the transport properties of graphene under inhomogeneous strain are studied. We find that the Landau levels have non-zero group velocity, and construct one-dimensional conducting channels...

We study the disorder-induced phase transition of higher-order Weyl semimetals (HOWSMs) and the fate of the topological features of disordered HOWSMs. We obtain a global phase diagram of HOWSMs according to the scaling theory of Anderson localization. Specifically, a phase transition from the Weyl semimetal (WSM) to the HOWSM is uncovered, distingu...

Though several theoretical models have been proposed to design electronic flat-bands, the definite experimental realization in two-dimensional atomic crystal is still lacking. Here we propose a novel and realistic flat-band model based on threefold degenerate p-orbitals in two-dimensional ionic materials. Our theoretical analysis and first-principl...

Disorder effects inevitably exist in realistic samples, manifesting in various physical properties. In this paper, we review the recent progress in understanding the disorder effects on quantum transport and quantum phase transition properties in low-dimensional superconducting and topological systems. As a consequence of the pronounced quantum flu...

The quantum anomalous Hall effect (QAHE), carrying dissipationless chiral edge states, occurs without any magnetic field. Two main strategies were proposed to host QAHE: the magnetic topological insulator thin films and graphene systems. Only the former one was realized in experiment at low temperature. In this paper, by dealing with the two-dimens...

Recently, the search for an axion insulator state in 3D magnetic topological insulators (TIs) has attracted intensive interest due to its unqiue electromagnetic response. However, the detection of the axion insulator state remains difficult in experiments. We systematically investigate the disorder-induced phase transition of the axion insulator st...

Inside a three-dimensional strong topological insulator, a tube with h/2e magnetic flux carries a pair of protected one-dimensional linear fermionic modes. This phenomenon is known as the “wormhole effect.” In this work, we find that the wormhole effect, as a unique degree of freedom, introduces exotic transport phenomena and thus manipulates the t...

In this work, we study the effects of disorder on topological metals that support a pair of helical edge modes deeply embedded inside the gapless bulk states. Strikingly, we predict that a quantum spin Hall (QSH) phase can be obtained from such topological metals without opening a global band gap. To be specific, disorder can lead to a pair of robu...

Spin photogalvanic effect (SPGE) is an efficient method to generate a spin current by photoexcitation in a contactless and ultra-fast way. In two-dimensional (2D) collinear antiferromagnetic (AFM) materials that preserve the combined time-reversal (T) and inversion (I) symmetry (i.e., TI symmetry), we find that the photogalvanic currents in two mag...

The quantum Hall effect (QHE) is broadly studied in the films of semiconductors, conductors, topological insulators, and topological semimetals. Wedge-shaped samples, guaranteeing the uniform properties of materials, bring obscure characteristics connected to the sample geometry. Here we study the QHE in wedge-shaped samples by using a simple elect...

Coupled quantum dots (QDs), usually referred to as artificial molecules, are important not only in exploring fundamental physics of coupled quantum objects, but also in realizing advanced QD devices. However, previous studies have been limited to artificial molecules with nonrelativistic fermions. Here, we show that relativistic artificial molecule...

Ferroelectriclike metals are a relatively rare class of materials that have ferroelectriclike distortion and metallic conductivity. LiOsO3 is the first demonstrated and the most investigated ferroelectriclike metal. The presence of free carriers makes them difficult to be studied by traditional ferroelectric techniques. In this paper, using symmetr...

We investigate the 3D quantum Hall effect in Weyl semimetals and elucidate a global picture of the edge states. The edge states hosting 3D quantum Hall effect are combinations of Fermi arcs and chiral Landau bands dispersing along the magnetic field direction. The Hall conductance, σxzH [see Fig. 4], shows quantized plateaus with the variance of th...

In this Letter, we study an Anderson-localization-induced quantized transport in disordered Chern insulators (CIs). By investigating the disordered CIs with a step potential, we find that the chiral interface states emerge along the interfaces of the step potential, and the energy range for such quantized transport can be manipulated through the po...

We numerically demonstrate that the topological corner states residing in the corners of higher-order topological insulator possess non-Abelian braiding properties. Such topological corner states are Dirac fermionic modes other than Majorana zero modes. We claim that Dirac fermionic modes protected by nontrivial topology also support non-Abelian br...

Inside a three-dimensional strong topological insulator, a tube with $h/2e$ magnetic flux carries a pair of protected one-dimensional linear fermionic modes. This phenomenon is known as the "wormhole effect". In this work, we find that the "wormhole effect", as a unique degree of freedom, introduces exotic transport phenomena and thus manipulates t...

Majorana zero modes (MZMs)—bearing potential applications for topological quantum computing—are verified in quasi-one-dimensional (1D) fermion systems, including semiconductor nanowires, magnetic atomic chains, and planar Josephson junctions. However, the existence of multibands in these systems makes the MZMs fragile to the influence of disorder....

Ferroelectric-like metals are a relatively rare class of materials that have ferroelectric-like distortion and metallic conductivity. LiOsO$_3$ is the first demonstrated and the most investigated ferroelectric-like metal. The presence of free carriers makes them difficult to be studied by traditional ferroelectric techniques. In this paper, using t...

Piezotronics is an emerging field, which exploits strain to control the transport properties in condensed matters. At present, piezotronics research majorly focuses on insulators with tunable electric dipole by strain. Metals are excluded in this type of application due to the absence of the electric dipole. The recently discovered Berry-curvature...

We study the disorder-induced phase transition in two-dimensional non-Hermitian systems. First, the applicability of the noncommutative geometric method (NGM) in non-Hermitian systems is examined. By calculating the Chern number of two different systems (a square sample and a cylindrical one), the numerical results calculated by NGM are compared wi...

We propose a flat band model based on degenerate $p$ orbitals at the centers of octahedrons which are closely-packed in a two-demensional structure. Our theoretical analysis and first-principles calculations show that the proposed flat band can be realized in 1T layered materials of alkali-metal chalogenides and metal-carbon group compounds. Some o...

Ever since its first proposal in 1976, Jackiw-Rebbi zero-mode has been drawing extensive attention for its charming properties including charge fractionalization, topologically protected zero-energy and possible non-Abelian statistics. We investigate these properties through the Jackiw-Rebbi zero-modes in quantum spin Hall insulators. Though charge...

We investigate the 3D quantum Hall effect in Weyl semimetals and elucidate a global picture of the edge states. The edge states hosting 3D quantum Hall effect are combinations of Fermi arcs and chiral bulk Landau levels parallel to the magnetic field. The Hall conductance, $\sigma_{xz}^H$, shows quantized plateaus at Weyl nodes while tuning the mag...

Scaling theory predicts complete localization in d = 2 in quantum systems belonging to the orthogonal class (i.e., with time-reversal symmetry and spin-rotation symmetry). The conductance g behaves as g ∼ exp(—L/l) with system size L and localization length l in the strong disorder limit. However, classical systems can always have metallic states i...

Based on the tight-binding calculations on honeycomb lattice and photonic experimental visualization on artificial graphene (AG), we report the domain-wall-induced gapped topological kink states and topological corner states. In honeycomb lattice, domain walls (DWs) with gapless topological kink states could be induced either by sublattice symmetry...

We numerically demonstrate that the topological corner states residing in the corners of higher-order topological insulator possess non-Abelian braiding properties. Such topological corner states are Dirac fermionic modes other than Majorana zero-modes. We claim that Dirac fermionic modes protected by nontrivial topology also support non-Abelian br...

In this paper, we investigate the realization of topological Anderson insulators in electric circuits. A disordered Haldane model is constructed through electric circuit networks composed of capacitors and inductors, where the disorder is introduced through the random induction of the grounding inductors. Based on the noncommutative geometry method...

Piezotronics is an emerging field, which exploits strain to control the transport properties in condensed matters. At present, piezotronics research majorly focuses on insulators with tunable electric dipole by strain. Metals are excluded in this type of applications due to the absence of electric dipole. The recently discovered Berry curvature dip...

In addition to the giant peak of the nonlocal resistance RNL, an anomalous negative value of RNL has been observed in graphene systems, although its formation mechanism is not quite understood yet. In this work, utilizing the nonequilibrium Green's function method, we calculate the local-current flow in an H-shaped noninteracting graphene system lo...

Previous studies presented the phase diagram induced by the disorder existing separately either in the higher-order topological states or in the topological trivial states, respectively. However, the influence of disorder on the system with the coexistence of the higher-order topological states and other traditional topological states has not been...

Majorana zero modes (MZMs)--bearing potential applications for topological quantum computing--are verified in quasi-one-dimensional (1D) Fermion systems, including semiconductor nanowires, magnetic atomic chains, planar Josephson junctions. However, the existence of multi-bands in these systems makes the MZMs fragile to the influence of disorder. M...

Using low-temperature high-magnetic-field scanning tunneling microscopy and spectroscopy (STM/STS), we systematically study a graphene quantum dot (GQD) defined by a circular graphene p-p junction. Inside the GQD, we observe a series of quasi-bound states arising from whispering-gallery-mode (WGM) confinement of the circular junction and directly v...

Coupled quantum dots (QDs), usually referred to as artificial molecules, are important not only in exploring fundamental physics of coupled quantum objects, but also in realizing advanced QD devices. However, previous studies have been limited to artificial molecules with nonrelativistic fermions. Here, we show that relativistic artificial molecule...