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Gongqi Wang

Publications and source records attributed to Gongqi Wang.

3 recordsLinked to original sources

Theoretical study of superconducting diode effect in planar $T_{d}-MoTe_{2}$ Josephson junctions

We investigate the Josephson diode effect (JDE) within quasi-2D planar systems featuring the $C_{1v}$ spin-orbit coupling (SOC) and Zeeman fields in the normal region. Our analysis is based on experimental observations conducted on $MoTe_{2}$ planar Josephson junctions (JJ) subjected to out-of-plane magnetic fields. We emphasize the pivotal role of symmetry breaking in current directionality for the occurrence of the JDE. Specifically, we observe the emergence of asymmetric Andreev bound states (ABSs) and $0$-$π$-like transitions with $φ_0$-shifts in the current phase relations (CPRs) in systems with specific symmetry breaking induced by SOC and Zeeman fields, leading to different critical current magnitudes in opposite directions. Additionally, we explore the influence of parameters such as the strength of SOC, Zeeman field magnitude and orientation, conduction channels with different transverse momenta, and junction lengths on the JDE efficiencies. Our results indicate the potential for diverse approaches to modulate efficiencies and provide insights that can aid in the discovery of materials and design of Josephson diodes with significantly enhanced efficiency.

cond-mat.supr-con

Edelstein effect induced superconducting diode effect in inversion symmetry breaking MoTe$_2$ Josephson junctions

Superconducting diode effect (SDE) with nonreciprocal supercurrent transport has attracted intense attention recently, not only for its intriguing physics, but also for its great application potential in superconducting circuits. It is revealed in this work that planar Josephson junctions (JJs) based on type-II Weyl semimetal (WSM) MoTe$_2$ can exhibit a prominent SDE due to the emergence of asymmetric Josephson effect (AJE) in perpendicular magnetic fields. The AJE manifests itself in a very large asymmetry in the critical supercurrents with respect to the current direction. The sign of this asymmetry can also be effectively modulated by the external magnetic field. Considering the special noncentrosymmetric crystal symmetry of MoTe$_2$, this AJE is understood in terms of the Edelstein effect, which induces a nontrivial phase shift in the current phase relation of the junctions. Besides these, it is further demonstrated that the rectification of supercurrent in such MoTe$_2$ JJs with the rectification efficiency up to 50.4%, unveiling the great application potential of WSMs in superconducting electronics.

cond-mat.supr-con

Time-dependent Andreev reflection

We extend the basic theory of Andreev reflection (AR) in a normal metal/superconductor junction to the situation with an arbitrary time-dependent bias voltage $V(t)$ across the junction. The central element of the theory is the fact that the Fourier transform of the AR amplitude has a casual structure. As an example, the theory is used to describe the current response to short pulses of the bias voltage, which create coherent superposition of quasiparticle states with different energies. The current oscillates in time, with the gap frequency $Δ/\hbar$, and also as a function of the pulse area $\int V(t)dt$, with the period of the single-electron flux quantum $e/h$.

cond-mat.mes-hall