arXiv subjects

Sun Qing-feng

Publications and source records attributed to Sun Qing-feng.

2 recordsLinked to original sources

arXiv2018

Influence of magnetic disorders on Quantum Anomalous Hall Effect in Magnetic Topological Insulator Films beyond the two-dimensional limit

Quantum anomalous Hall effect (QAHE) has been experimentally realized in magnetic topological insulator (MTI) thin films fabricated on magnetically doped (Bi,Sb)2Te3. In a MTI thin film with the magnetic easy axis along the normal direction (z-direction), orientations of magnetic dopants are randomly distributed around the magnetic easy axis, acting as magnetic disorders. With the aid of the non-equilibrium Green's function and Landauer-Buttiker formalism, we numerically study the influence of magnetic disorders on QAHE in a MTI thin film modeled by a three-dimensional tight-binding Hamiltonian. It is found that, due to the existence of gapless side surface states, QAHE is protected even in the presence of magnetic disorders as long as the z-component of magnetic moment of all magnetic dopants are positive. More importantly, such magnetic disorders also suppress the dissipation of the chiral edge states and enhance the quality of QAHE in MTI films. In addition, the effect of magnetic disorders depends very much on the film thickness, and the optimal influence is achieved at certain thickness. These findings are new features for QAHE in three-dimensional systems, not present in two-dimensional systems.

cond-mat.mes-hall↗

arXiv2017

Low-energy electronic properties of Weyl semimetal quantum dot

It is necessary to study the properties of Weyl semimetal nanostructures for potential applications in nanoelectronics. Here we study the Weyl semimetal quantum dot with a most simple model Hamiltonian with only two Weyl points. We focus on the low-energy electronic structure and show the correspondence to that of three-dimensional Weyl semimetal, such as Weyl point and Fermi arc. We find that there exist both surface and bulk states near Fermi level. The direct gap of bulk states reaches the minimum with the location determined by Weyl point. There exists a quantum number with only several values supporting surface states, which is the projection of Fermi arc. The property of surface state is studied in detail, including circular persistent current, orbital magnetic moment, and chiral spin polarization. Surface states will be broken by a strong magnetic field and evolve into Landau levels gradually. Simple expressions are derived to describe the energy spectra and electronic properties of surface states both in the presence and absence of magnetic field. In addition, this study may help design a method to verify Weyl semimetal by separating out the signal of surface states since quantum dot has the largest surface-to-volume ratio.

cond-mat.mes-hall↗