Controllable Andreev retroreflection and specular Andreev reflection in a four-terminal graphene-superconductor hybrid system

TL;DR

This paper explores how quantum interference in a four-terminal graphene-superconductor system enables control and separation of Andreev reflections, with implications for quantum device design.

Contribution

It demonstrates that phase difference controls the coexistence and suppression of specular and retro Andreev reflections in a graphene-superconductor hybrid system.

Findings

Specular Andreev reflection vanishes at phase difference θ=0.

Retroreflection disappears at phase difference θ=π.

Reflected holes exit from both terminals in narrow nanoribbons.

Abstract

We report the investigation of electron transport through a four-terminal graphene-superconductor hybrid system. Due to the quantum interference of the reflected holes from two graphene-superconductor interfaces with phase difference $\theta$, it is found that the specular Andreev reflection vanishes at $\theta=0$ while the Andreev retroreflection disappears at $\theta=\pi$. This means that the retroreflection and specular reflection can be easily controlled and separated in this device. In addition, due to the diffraction effect in the narrow graphene nanoribbon, the reflected hole can exit from both graphene terminals. As the width of nanoribbon increases, the diffraction effect gradually disappears and the reflected hole eventually exits from a particular graphene terminal depending on the type of Andreev reflection.