arXiv subjects

W. Y. Deng

Publications and source records attributed to W. Y. Deng.

8 recordsLinked to original sources

arXiv2019

Quantum-oscillation-modulated angular dependences of the positive longitudinal magnetoconductivity and planar Hall effect in Weyl semimetals

We study the positive longitudinal magnetoconductivity (LMC) and planar Hall effect as emergent effects of the chiral anomaly in Weyl semimetals, following a recent-developed theory by integrating the Landau quantization with Boltzmann equation. It is found that, in the weak magnetic field regime, the LMC and planar Hall conductivity (PHC) obey $\cos^{6}θ$ and $\cos^{5}θ\sin θ$ dependences on the angle $θ$ between the magnetic and electric fields. For higher magnetic fields, the LMC and PHC cross over to $\cos^{2}θ$ and $\cosθ\sinθ$ dependences, respectively. Interestingly, the PHC could exhibit quantum oscillations with varying $θ$, due to the periodic-in-$1/B$ oscillations of the chiral chemical potential. When the magnetic and electric fields are noncollinear, the LMC and PHC will deviate from the classical $B$-quadratic dependence, even in the weak magnetic field regime.

cond-mat.mes-hall↗

arXiv2017

Inverse Edelstein effect of the surface states of a topological insulator

The surface states of three-dimensional topological insulators posses the unique property of spin-momentum interlocking. This property gives rise to the interesting inverse Edelstein effect (IEE), in which an applied spin bias $μ$ is converted to a measurable charge voltage difference $V$. We develop a semiclassical theory for the IEE of the surface states of $\text{Bi}_2\text{Se}_3$ thin films, which is applicable from the ballistic regime to diffusive regime. We find that the IEE efficiency ratio $γ=V/μ$ exhibits universal dependence on sample size, and approaches $π/4$ in the ballistic limit and $1$ in the diffusive limit.

cond-mat.mes-hall↗

arXiv2016

Experimental observation of anisotropic Adler-Bell-Jackiw anomaly in type-II Weyl semimetal WTe$_{1.98}$ crystals at the quasi-classical regime

The asymmetric electron dispersion in type-II Weyl semimetal theoretically hosts anisotropic transport properties. Here we observe the significant anisotropic Adler-Bell-Jackiw (ABJ) anomaly in the Fermi-level delicately adjusted WTe$_{1.98}$ crystals. Quantitatively, $C_w$ , a coefficient representing intensity of ABJ anomaly, along a- and b-axis of WTe$_{1.98}$ are 0.030 and 0.051 T$^{-2}$ at 2 K, respectively. We found that temperature-sensitive ABJ anomaly is attributed to topological phase transition from type-II Weyl semimetal to trivial semimetal, which is verified by first-principles calculation using experimentally determined lattice parameters at different temperatures. Theoretical electrical transport study reveals that observation of ansotropic ABJ both along a- and b-axis in WTe$_{1.98}$ is attributed to electrical transport in the quasi-classical regime. Our work may suggest that electron-doped WTe$_2$ is an ideal playground to explore the novel properties in type-II Weyl semimetals.

cond-mat.mtrl-sci↗

arXiv2016

Analytical theory and possible detection of the $ac$ quantum spin Hall effect

We develop an analytical theory of the low-frequency $ac$ quantum spin Hall (QSH) effect based upon the scattering matrix formalism. It is shown that the $ac$ QSH effect can be interpreted as a bulk quantum pumping effect. When the electron spin is conserved, the integer-quantized $ac$ spin Hall conductivity can be linked to the winding numbers of the reflection matrices in the electrodes, which also equal to the bulk spin Chern numbers of the QSH material. Furthermore, a possible experimental scheme by using ferromagnetic metals as electrodes is proposed to detect the topological $ac$ spin current by electrical means.

cond-mat.mes-hall↗

arXiv2016

Effect of the edge states on the conductance and thermopower in Zigzag Phosphorene Nanoribbons

We numerically study the effect of the edge states on the conductance and thermopower in zigzag phosphorene nanoribbons (ZPNRs) based on the tight-binding model and the scattering-matrix method. It is interesting to find that the band dispersion, conductance, and thermopower can be modulated by applying a bias voltage and boundary potentials to the two layers of the ZPNRs. Under the certain bias voltage, the two-fold degenerate quasi-flat edge bands split perfectly. The conductance can be switched off, and the thermopower around zero energy increases. In addition, when only the boundary potential of the top layer or bottom layer is adjusted, only one edge band bends and merges into the bulk band. The first conductance plateau is strongly decreased to $e^2/h$ around zero energy. Particularly, when the two boundary potentials are adjusted, all the edge bands bend and fully merge into the bulk band, and the bulk energy gap is maximized. More interestingly, a pronounced conductance plateau with $G=0$ is found around zero energy, which is attributable to the opening of the bulk energy gap between the valence and conduction bands. Meanwhile, the thermopower can be enhanced more than twice, compared to that of the perfect ZPNRs. The large magnitude of thermopower is ascribed to the appearance of the bulk energy gap around zero energy. Our results show that the modulated ZPNRs are more reliable in thermoelectric application.

cond-mat.mes-hall↗

arXiv2016

Robust AC Quantum Spin Hall Effect without Participation of Edge States

The quantum spin Hall (QSH) effect in the DC regime, which has been intensively researched, relies on the existence of symmetry-protected edge states. Here, we demonstrate that a QSH system behaves quite differently in response to an applied AC electric field, and put forward the idea of AC QSH effect. The AC QSH effect can occur in the bulk without involving the fragile edge states, hence being robust against time-reversal symmetry breaking and disorder. It lays a more solid foundation for practical applications of the two-dimensional topological insulators, in the emerging field of AC spintronics.

cond-mat.mes-hall↗

arXiv2016

Unified Theoretical Approach to Electronic Transport from Diffusive to Ballistic Regimes

We show that by integrating out the electric field and incorporating proper boundary conditions, a semiclassical Boltzmann equation can describe electron transport properties, continuously from the diffusive to ballistic regimes. General analytical formulas of the conductance in $D=1,2,3$ dimensions are obtained, which recover the Boltzmann-Drude formula and Landauer-Büttiker formula in the diffusive and ballistic limits, respectively. This intuitive and efficient approach can be applied to investigate the interplay of system size and impurity scattering in various charge and spin transport phenomena.

cond-mat.mes-hall↗

arXiv2016

Non-adiabatic topological spin pumping

Based on the Floquet scattering theory, we analytically investigate the topological spin pumping for an exactly solvable model. Floquet spin Chern numbers are introduced to characterize the periodically time-dependent system. The topological spin pumping remains robust both in the presence and in the absence of the time-reversal symmetry, as long as the pumping frequency is smaller than the band gap, where the electron transport involves only the Floquet evanescent modes in the pump. For the pumping frequency greater than the band gap, where the propagating modes in the pump participate in the electron transport, the spin pumping rate decays rapidly, marking the end of the topological pumping regime.

cond-mat.mes-hall↗