Andreev reflection in graphene nanoribbons

TL;DR

This paper investigates how the finite size of graphene nanoribbons affects Andreev reflection in hybrid junctions with superconductors, revealing size-dependent suppression or enhancement of reflection due to pseudoparity conservation.

Contribution

It demonstrates the impact of finite-size effects and pseudoparity on Andreev reflection, providing new insights into quantum transport in graphene nanoribbons.

Findings

Even-site ribbons suppress Andreev reflection, leading to insulating behavior.

Odd-site ribbons exhibit perfect Andreev reflection.

Gate voltage can restore conduction in even-site ribbons.

Abstract

We study Andreev reflection in graphene nanoribbon/superconductor hybrid junctions. By using a tight-binding approach and the scattering formalism we show that finite-size effects lead to notable differences with respect to the bulk graphene case. At subgap voltages, conservation of pseudoparity, a quantum number characterizing the ribbon states, yields either a suppression of Andreev reflection when the ribbon has an even number of sites in the transverse direction or perfect Andreev reflection when the ribbon has an odd number of sites. In the former case the suppression of Andreev reflection induces an insulating behavior even when the junction is biased; electron conduction can however be restored by applying a gate voltage.