arXiv subjects

G. Y. Qi

Publications and source records attributed to G. Y. Qi.

3 recordsLinked to original sources

arXiv2021

Theoretical study for 3D quantum Hall effect in a periodic electron system

The exsitance of three-dimensional Hall effect (3DQHE) due to spontaneous Fermi surface instabilities in strong magnetic field was proposed decades ago, and has stimulated recent progress in experiments. The reports in recent experiments show that the Hall plateaus and vanishing transverse magneto-resistivities (TMRs) (which are two main signatures of 3DQHE) are not easy to be observed in natural materials. And two main different explanations of the slow varying slope like Hall plateaus and non-vanishing TMRs (which can be called as quasi-quantized Hall effect (QQHE)) have been proposed. By studying the magneto-transport with a simple effective periodic 3D system, we show how 3DQHE can be achieved in certain parameter regimes at first. We find two new mechanisms that may give rise to QQHE. One mechanism is the "low" Fermi energy effect, and the other is the "strong" impurity effect. Our studies also proved that the artificial superlattice is an ideal platform for realizing 3DQHE with high layer barrier periodic potential.

cond-mat.mes-hall↗

arXiv2019

Superconducting states and Majorana modes in transition-metal dichalcogenides under inhomogeneous strain

We study the effect of inhomogeneous strain on transition-metal dichalcogenides with a large intrinsic gap in their spectrum. It is found that, by tuning the chemical potential, superconductivity can preserve within the strain-induced discrete pseudo Landau levels (LLs), which introduce interesting topological properties to these systems. As we show, the superconductivity for integer fillings is quantum critical, and the quantum critical coupling strength is determined by the spacing between the two LLs closest to the Fermi level. For partial fillings, the superconducting gap is scaled linearly with the coupling strength, and decreases rapidly when the chemical potential shifts away from the middle of each LL. In the presence of a Zeeman field, a pair of Majorana modes emerge simultaneously in the two valleys of strained dichalcogenides. When valley symmetry is further destroyed, a single Majorana mode can be expected to emerge at the edges of the strained monolayer dichalcogenides.

cond-mat.mes-hall↗

arXiv2018

Quantum Oscillations of The Positive Longitudinal Magnetoconductivity: a Fingerprint for Identifying Weyl Semimetals

Weyl semimetals (WSMs) host charged Weyl fermions as emergent quasiparticles. We develop a unified analytical theory for the anomalous positive longitudinal magnetoconductance (LMC) in a WSM, which bridges the gap between the classical and ultra-quantum approaches. More interestingly, the LMC is found to exhibit periodic-in-$1/B$ quantum oscillations, originating from the oscillations of the nonequilibrium chiral chemical potential. The quantum oscillations, superposed on the positive LMC, are a remarkable fingerprint of a WSM phase with chiral anomaly, whose observation is a valid criteria for identifying a WSM material. In fact, such quantum oscillations were already observed by several experiments.

cond-mat.mes-hall↗