arXiv subjects

Yi-Xiang Wang

Publications and source records attributed to Yi-Xiang Wang.

At least 19 recordsLinked to original sources

arXiv2026

Two-dimensional bound excitons in real space and Landau quantization space: A comparative study

The Landau quantization space is based on the respective motion of the electron and hole in a magnetic field and can provide a new route to understand the bound exciton behaviors observed in the experiments. In this paper, we study the two-dimensional exciton properties of monolayer WSe$_2$ in both real space and Landau quantization space. Focusing on the excitons of zero center-of-mass momentum, we calculate its energy spectrum in both spaces, with the results agreeing well with each other. We then obtain the diamagnetic coefficients and root-mean-square radius, which are consistent with the available $s$ state data in the experiment. More importantly, in the exciton state $nl$, we find that the dominant electron-hole pair component may shift with the magnetic field and the Coulomb interactions, and reveal that the magnetic field will drive the dominant component to be the free electron-hole pair $\{n_e=n+l-1,n_h=n-1\}$, whereas the Coulomb interactions drives it to be the pair of the lower index.

cond-mat.mes-hall↗

arXiv2026

Quantum oscillations and nonsaturating magnetoresistivity in nodal-line semimetals

Understanding the magnetotransport behaviors in topological systems remains alluring, as a lot of intrinsic information could be extracted, e.g., the band structures, Berry phase, Fermi surface, carrier density, and so on. Motivated by the recent magnetotransport developments in nodal-line semimetal, EuGa4, in this paper, we will study the magnetotransport properties of the system, focusing on the quantum oscillations and nonsaturating magnetoresistivity (MR). Firstly, we analyze the chemical potential and magnetoconductivity oscillations with the magnetic field and reveal that there exist two distinct oscillation frequencies, which are caused by the characteristic torus Fermi surface and can be regarded as an important experimental signature of nodal-line semimetals. Then we calculate the MR and find that although the MR is nonsaturating with the magnetic field in the low-energy region, the MR ratio is much smaller than that reported in the experiment.

cond-mat.mes-hall↗

arXiv2025

Magnetotransport and activation energy of the surface states in Cd3As2 thin films

Recent experiments performed the magnetotransport measurements in (001)-oriented Cd$_3$As$_2$ thin films and attributed the magnetotransport properties to the surface states. In this paper, by using an effective model to describe the surface states, we analyze the Landau bands and then calculate the magnetoconductivities and magnetoresistivities. From these results, the features of two-dimensional quantum Hall effect of the surface states can be captured. More importantly, we reveal that the activation energy is determined by the Hall plateau width, which can explain the experimental observations that the activation energies at odd plateaus are larger than those at even plateaus. We also analyze the roles played by the structural inversion symmetry breaking and impurity scatterings in the magnetotransport, and suggest that their combined effects would lead to the absence of some Hall plateaus.

cond-mat.mes-hall↗

arXiv2025

Electron-transverse acoustic phonon couplings in three-dimensional pentatellurides

Transverse acoustic (TA) phonon waves are analogous to electromagnetic waves and can carry a certain angular momentum. In this paper, we study the electron-TA phonon couplings in three-dimensional pentatellurides and explore the conditions under which the TA phonon condensation is stable. We analyze the Lindhard response function, phonon softening, mean-field parameters, and renormalized dispersions, on the basis of which the phase diagrams of the electron-phonon couplings in ZrTe$_5$ and HfTe$_5$ are calculated. The phase diagrams show that, if the chemical potential lies near the Weyl nodes, the TA phonon condensation will dominate and lead to the shear strain wave phase. We further reveal that when the wave vector of the particular phonon mode is smaller, the critical coupling strength will be weaker for the phonon condensation, which thus favors the condensation phase.

cond-mat.mes-hall↗

arXiv2024

Quantum theory of the magnetochiral anisotropy coefficient in ZrTe$_5$

Recent experiments performed the nonreciprocal magneotransport in ZrTe$_5$ and obtained a giant magnetochiral anisotropy (MCA) coefficient $γ'$. The existing theoretical analysis was based on the semiclassical Boltzmann equation. In this paper, we develop a full quantum theory to calculate $γ'$ and further explore the underlying physics. We reveal that the $xz$-mirror symmetry breaking term also breaks the parity symmetry of the system and leads to mixed selection rules and nonvanishing second-order conductivity $σ_{xxx}$. The calculations show that $γ'$ decreases with the magnetic field, survives only to weak impurity scatterings, and exhibits a nonmonotonous dependence on the strength of the $xz$-mirror symmetry breaking. Our paper can provide a deeper insight into the intrinsic nonreciprocal magnetotransport phenomena in the topological semimetal material.

cond-mat.mes-hall↗

arXiv2023

Magnetic field driven Lifshitz transition and one-dimensional Weyl nodes in three-dimensional pentatellurides

Recent experiments reported that the magnetic field can drive the Lifshitz transition and one-dimensional (1D) Weyl nodes in the quantum limit of three-dimensional pentatellurides, as they own low carrier densities and can achieve the extreme quantum limit at a low magnetic field. In this paper, we will investigate the conditions for the existence of the 1D Weyl nodes and their dc transport properties. We find that in the strong topological insulator (TI) phase of ZrTe5, the formation of the Weyl nodes depends heavily on the carrier density; while in the weak TI phase of HfTe5, the Weyl nodes are more likely to appear. These behaviors are attributed to the fact that in the strong and weak TI phases, the zeroth Landau levels exhibit opposite evolutions with the magnetic field. Moreover, the signatures of the critical fields that characterize the distinct behaviors of the system can be directly captured in the conductivities.

cond-mat.mes-hall↗

arXiv2023

Quantum oscillations and three-dimensional quantum Hall effect in ZrTe$_5$

Recent experiments have reported a lot of spectacular transport properties in topological materials, such as quantum oscillations and three-dimensional (3D) quantum Hall effect (QHE) in ZrTe$_5$. In this paper, by using a strong topological insulator model to describe ZrTe$_5$, we study the magnetotransport property of the 3D system. With fixed carrier density, we find that there exists a deferring effect in the chemical potential, which favors distinguishing the saddle points of the inverted LLs. On the other hand, with fixed chemical potential, the features of 3D QHE are demonstrated and we attribute the underlying mechanisms to the interplay between Dirac fermions, magnetic field and impurity scatterings.

cond-mat.mes-hall↗

arXiv2023

Full investigation of nonadiabatic dynamical characterization in arbitrary quenching process

Recently, dynamical characterization of bulk topology has been experimentally realized under nonadiabatic sudden quench dynamics. However, it has been shown that only the topology of final phase can be characterized when the system is quenched from initial topologically trivial phase. In this paper, taking the two-dimensional Chern insulator as an example, we make a thorough investigation of different types of quenching processes under nonadiabatic slow quench dynamics, and study not only the processes between nontrivial phase and trivial phase, but also between the phases with different topological invariants. We find that, under slow quench dynamics, both the initial and final topological phase can be characterized and the topological invariant can be captured by time-averaged spin polarization. Moreover, different types of processes can be distinguished from the special regions where the time-averaged spin polarization vanishes. All the dynamical characterization schemes are entirely based on the experimentally measurable quantity time-averaged spin polarization, and thus one can expect our findings may provide reference for future experiments.

quant-ph↗

arXiv2022

Unconventional optical selection rules in ZrTe5 under an in-plane magnetic field

The optical selection rules of an electron system under a magnetic field play key roles in determining its optical properties, from which the band structures and underlying symmetries can be derived. In this Letter, based on a three-dimensional strong topological insulator model describing ZrTe5,we study the Landau levels (LLs) and magneto-optical conductivity under an in-plane magnetic field. We reveal that in the transverse conductivity Re(σ_{zz}), the unconventional optical selection rules n\righatarrow n\pm 2 dominate, with n being the LL index. We attribute the unconventional selection rules to the peculiar distribution of parity carried by the LLs, resulting from the chiral symmetry of the sub-Hamiltonians. Moreover, we predict that, if the strong anisotropic system is tuned to be nearly isotropic, the LLs would redistribute and the conventional selection rules n\rightarrow n\pm 1 can be recovered.

cond-mat.mes-hall↗

arXiv2022

High Chern number phase in topological insulator multilayer structures: a Dirac cone model study

We use the Dirac cone model to explore the high Chern number (C) phases that are realized in the magnetic-doped topological insulator (TI) multilayer structures by Zhao et al. [Nature 588, 419 (2020)]. The Chern number is calculated by capturing the evolution of the phase boundaries with the parameters and then the Chern number phase diagrams of the TI multilayer structures are obtained. The high-C behavior is attributed to the band inversion of the renormalized Dirac cones, along with which the spin polarization at the Γpoint will get increased. Moreover, another two TI multilayer structures as well as the TI superlattice structures are also studied.

cond-mat.mes-hall↗

arXiv2022

Generic theory of characterizing topological phases under quantum slow dynamics

Dynamical characterization of equilibrium topological phases has attracted considerable attention in recent years. In this paper, we make a thorough exploration of the non-adiabatic characterization of topological phases under slow quench protocol. We first propose an exactly solvable multi-state Landau-Zener model that can be directly applied to the non-adiabatic slow quench dynamics of topological systems. Then we present two different schemes to characterize the bulk topology of the system based on the so called spin inversion surface. The first one needs least number of quenching processes, but requires to measure the gradients of time-averaged spin-polarization on the SIS. The second one only needs to measure the value of time-averaged spin-polarization on the SIS, thus makes it possible to directly characterize the topological phases by introducing an extra quenching process. Moreover, high-order SIS or band inversion surface (BIS) relying on the dimension reduction approach, is also generalized to the above two different characterization schemes. One can extract the topological invariant from pairs of points with opposite signs both on the 0D highest order BIS and on the 0D highest order SIS, which greatly simplifies the measurement strategy and characterization process. In a word, superior to the sudden quench protocol, we demonstrate that the topological invariant can be captured not only by the topological information on BIS, but also on the SIS. In particular, direct characterization of topological phases based on BIS and SIS can be realized.

quant-ph↗

arXiv2021

Magneto-optic signatures in the gapped Dirac semimetal with mixed linear and parabolic dispersions of ZrTe5

In this paper, we give a systematic theoretical study on the Landau levels (LLs) and magneto-optical conductivity Re$(σ_{αα})$ in a gapped Dirac semimetal model with mixed linear and parabolic dispersions under a magnetic field, which was recently proposed by Jiang \textit{et al.} [Phys. Rev. Lett. {\bf125}, 046403 (2020)] to explain the experimental magnetoinfrared spectroscopy in the three-dimensional ZrTe$_5$ crystal. We find that the strong magnetic field can drive the LLs become noninverted and thus the strong topological insulator phase in ZrTe$_5$ turns to be a trivial insulator. In the different magnetic field regions, the density of states and Re$(σ_{αα})$ can exhibit distinct signatures. Moreover, when the magnetic field is weak, a qualitative relation in Re$(σ_{zz})$ between the peaks at the saddle points is revealed as Re$(σ_{zz}^{ζ_n})>$Re$(σ_{zz}^Γ)$, which is in good agreement with the experiment.

cond-mat.mes-hall↗

arXiv2021

Gapped Dirac semimetal with mixed linear and parabolic dispersions

In this paper, we make a comprehensive study of the properties of a gapped Dirac semimetal model, which was originally proposed in the magnetoinfrared spectroscopy measurement of ZeTe$_5$, and includes both the linear and parabolic dispersions in all three directions. We find that, depending on the band inversion parameters, $ζ'$ and $ζ_z'$, the model can support three different phases: the single Dirac point (DP) phase, the double DPs phase and the Dirac ring phase. The three different phases can be distinguished by their low-energy features in the density of states (DOS) and optical conductivity. At high energy, both the DOS and optical conductivity exhibit power-law like behaviors, with the asymptotic exponents depending heavily on the signs of $ζ'$ and $ζ_z'$. Moreover, the thumb-of-rule formula between the DOS and optical conductivity is satisfied only when $(ζ',ζ_z')>0$. The implications of our results for experiments are discussed.

cond-mat.mes-hall↗

arXiv2021

High-Chern number phase in the topological insulator multilayer structures

The high-Chern number phases with a Chern number C>1 have been observed in a recent experiment that performed on the topological insulator (TI) multilayer structures, consisting of the alternating magnetic-doped and undoped TI layers. In this paper, we develop an effective method to determine the Chern numbers in the TI multilayer structures and then make a systematic study on the Chern number phase diagrams that are modulated by the magnetic doping and the middle layer thickness. We point out that in the multilayer structure, the high-C behavior can be attributed to the band inversion mechanisms. Moreover, we find that the lowest bands may be multifold degenerate around the Gamma point, and when they are inverted, the Chern number change will be larger than one. Besides the TI multilayer structures implemented in the experiment, we also explore the high-C phase realizations in two other kinds of the TI multilayer structures. The implications of our results for experiments are discussed.

cond-mat.mes-hall↗

arXiv2021

Phase diagram and orbital Chern insulator in twisted double bilayer graphene

Compared with twisted bilayer graphene, twisted double bilayer graphene (TDBG) provides another important platform to realize the moiré flat bands. In this paper, we first calculate the valley Chern number phase diagram of TDBG in the parameter space spanned by the twist angle and the interlayer electric potential. To include the effects of interactions, we then phenomenologically introduce the spin-splitting and valley-splitting. We find that when the valley splitting is larger than the bandwidth of the first conduction band so that a gap is opened and the spin splitting is relatively weak, the orbital Chern insulator emerges at half-filling, associated with a large orbital magnetization (OM). Further calculations suggest that there is no sign reversal of the OM when the Fermi energy goes from the bottom to the top of the half-filling gap, as the OM remains negative in both AB-AB stacking and AB-BA stacking. The implications of our results for the ongoing experiments are also discussed.

cond-mat.mes-hall↗

arXiv2020

Examining the validity of the two-dimensional conical model to describe the three-dimensional ZrTe5

Understanding the low-energy excitation state in three-dimensional layered compound ZrTe5 remains a challenging problem in the study of novel topological materials. Recently, a two-dimensional conical model was proposed to explain the experimental optical spectroscopy in the 3D ZrTe5, Martino et al. [Phys. Rev. Lett. 122, 217402 (2019)]. Motivated by this work, in this paper, we perform a systematic theoretical study on the optical conductivity of this model in both cases without and with an external magnetic field to further demonstrate the validity of this model and to recover new physics.We find that there exist completely different characteristics for optical conductivity along different directions, due to anisotropic low-energy excitations in this two-dimensional conical model. Specifically, for the interband optical conductivity, we find asymptotic dependence on the optical frequency as Re(σ_x)\simω^{1/2} and Re(σ_z)\simω^{3/2}, which are universal both in the gapped insulator phase and Weyl semimetal phase. For the magneto-optical conductivity, on the contrary, Re(σ^B_{x/z}) shows distinct signatures in the gapped insulator phase and Weyl semimetal phase, which can help distinguish the two phases. Our results, to be verified in future experiments, could provide more insights into the understanding of the topological nature of ZrTe5.

cond-mat.mes-hall↗

arXiv2020

Disorder and magnetic transport in tilted Weyl semimetals

We investigate the effect of disorder on the Landau levels (LLs) in tilted three dimensional Weyl semimetals (WSMs) when a magnetic field is present. Based on the minimum lattice model and by using the exact diagonalization and Kubo's formula, we numerically calculate the Hall conductivity and the density of states (DOS), from which several striking signatures are found to distinguish type-I WSMs from type-II WSMs: the first is the response of the Hall conductivity to the Fermi energy around the band center in clean limit, the second is the performance of the Hall conductivity to disorder, where in type-I WSMs, the robustness of the low-energy LLs is broken successively from the higher LLs to the lower ones and can be understood with the sink down picture, and the third is the behavior of the DOS at zero energy to disorder. The implications of our results are discussed.

cond-mat.dis-nn↗

arXiv2020

Interaction-induced phase transitions of type-II Weyl semimetals

The study of Weyl semimetals (WSMs) lies at the forefront of the nontrivial topological phenomena in condensed-matter physics. In this work, we study the effect of on-site repulsive Hubbard interaction on the WSM system with a nonzero tilt at half filling. Within the Hartree-Fock mean-field approximation, we treat the Hubbard interaction self-consistently and find that the Fock exchange field vanishes, while the Hartree field can renormalize the topological mass, the tilt, and the Fermi velocity of the Weyl cones. When the renormalized tilt is larger than the renormalized Fermi velocity, the Hubbard interaction will induce the quantum phase transition from a type-I WSM to a type-II WSM. We then provide the interaction-induced phase diagrams of WSMs in different parametric spaces, in which the antiferromagnetic order at strong interaction is also considered. In addition, we analyze another model hosting two pairs of Weyl nodes, and similar results are obtained. The implications of these results are discussed.

cond-mat.str-el↗