Anisotropic Andreev reflection in semi-Dirac materials

TL;DR

This paper theoretically investigates how anisotropic properties of semi-Dirac materials influence Andreev reflection and conductance in normal-superconductor junctions, revealing orientation-dependent behaviors and crossover phenomena.

Contribution

It provides a detailed theoretical analysis of anisotropic Andreev reflection in semi-Dirac materials, highlighting orientation effects and the transition between retro and specular reflection modes.

Findings

Differential conductance varies with orientation and bias voltage.

Crossover from retro to specular Andreev reflection along linear dispersion.

Conductance oscillates or decays depending on dispersion direction.

Abstract

In the framework of Bogoliubov-de Gennes equation, we theoretically study the Andreev reflection in normal-superconducting junctions based on semi-Dirac materials. Owing to the intrinsic anisotropy of semi-Dirac materials, the configuration of Andreev reflection and differential conductance are strongly orientation-dependent. For the transport along the linear dispersion direction, the differential conductance exhibits a clear crossover from retro Andreev reflection to specular Andreev reflection with an increasing bias-voltage, and the differential conductance oscillates without a decaying profile when the interfacial barrier strength increases. However, for the transport along the quadratic dispersion direction, the boundary between the retro Andreev reflection and specular Andreev reflection is ambiguous, and the differential conductance decays with increasing the momentum mismatch or the interfacial barrier strength. We illustrate the pseudo-spin textures to reveal the underling physics behind the anisotropic coherent transport properties. These results enrich the understanding of the superconducting coherent transport in semi-Dirac materials.