Andreev reflection and subgap conductance in monolayer $MoS_2$ ferromagnet/$s$ and $d$-wave superconductor junction

TL;DR

This paper provides an exact theoretical analysis of Andreev reflection and subgap conductance in monolayer MoS2 ferromagnet/superconductor junctions, considering spin-valley coupling and anisotropic d-wave pairing effects.

Contribution

It introduces an exact formulation of electron-hole excitations in monolayer MoS2 and investigates the impact of spin-splitting and anisotropic superconducting gaps on Andreev reflection.

Findings

Distinct Andreev reflection behavior for spin-up and spin-down carriers.

Dependence of Andreev process on electron incidence angle.

Conditions for retro Andreev reflection in the system.

Abstract

The accurate and proper form of electron-hole excitations and corresponding Dirac-like spinors of monolayer molybdenum disulfide superconductor are exactly obtained. Andreev reflection and resulting subgap conductance in a $MoS_2$-based ferromagnetic superconducting (F/S) junction is accurately investigated in terms of dynamical characteristics of system. Due to spin-splitting energy gap in the valence band and nondegenerate $K$ and $K'$ valleys, the ferromagnetic exchange energy $\sigma h$ can cause a distinct behavior of Andreev process between spin-up and spin-down charge carriers belonging to different valleys. The chemical potential is necessarily fixed by a determined range in order to occur the retro Andreev reflection. Given one-particle superconducting bispinors enable us to explicitly involve the anisotropic superconducting gap $\Delta_S$ under electron-hole conversion, i.e., taking place in $d$-wave pair coupling. The effect of such gap is exactly explained in terms of the dependence of the Andreev process on the electron incidence angle at the interface.