Tunneling conductance in strained graphene-based superconductor: Effect of asymmetric Weyl-Dirac fermions

TL;DR

This paper explores how uniaxial strain in graphene alters tunneling conductance in superconductor junctions, revealing unique effects due to asymmetric Weyl-Dirac fermions and direction-dependent velocities.

Contribution

It introduces a model analyzing tunneling conductance in strained graphene with asymmetric Weyl-Dirac electrons, highlighting novel anisotropic Andreev reflection effects.

Findings

Andreev reflection depends on strain direction

Perpendicular current flows with no barrier in high asymmetry

Parallel current oscillates rapidly with gate voltage

Abstract

Based on the BTK theory, we investigate the tunneling conductance in a uniaxially strained graphene-based normal metal (NG)/ barrier (I)/superconductor (SG) junctions. In the present model, we assume that depositing the conventional superconductor on the top of the uniaxially strained graphene, normal graphene may turn to superconducting graphene with the Cooper pairs formed by the asymmetric Weyl-Dirac electrons, the massless fermions with direction-dependent velocity. The highly asymmetrical velocity, vy/vx>>1, may be created by strain in the zigzag direction near the transition point between gapless and gapped graphene. In the case of the highly asymmetrical velocity, we find that the Andreev reflection strongly depends on the direction and the current perpendicular to the direction of strain can flow in the junction as if there was no barrier. Also, the current parallel to the direction of strain anomalously oscillates as a function of the gate voltage with very high frequency. Our predicted result is found as quite different from the feature of the quasiparticle tunneling in the unstrained graphene-based NG/I/SG conventional junction. This is because of the presence of the direction-dependent-velocity quasiparticles in the highly strained graphene system.