Abstract

Interface bound states have been theoretically predicted to appear at isolated graphene-superconductor junctions. These states are formed at the interface due to the interplay between virtual Andreev and normal reflections and provide long range superconducting correlations on the graphene layer. We describe in detail the formation of these states from combining the Dirac equation with the Bogoliubov de Gennes equations of superconductivity. On the other hand, fluctuations of the low energy charge density in graphene have been confirmed as the dominating type of disorder. For analyzing the effect of disorder on these states we use a microscopic tight binding model. We show how the formation of these states is robust against the presence of disorder in the form of electron charge inhomogeneities in the graphene layer. We numerically compute the effect of disorder on the interface bound states and on the local density of states of graphene.

Highlights

  • The peculiar electronic band structure of graphene has been the focus of an intense research activity [1]

  • Interface bound states have been theoretically predicted to appear at isolated graphene-superconductor junctions

  • We show how the formation of these states is robust against the presence of disorder in the form of electron charge inhomogeneities in the graphene layer

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Summary

Introduction

The peculiar electronic band structure of graphene has been the focus of an intense research activity [1]. Graphene exhibits exotic effects like the Klein paradox—perfect transmission through potential barriers [2]. Good contacts can be achieved between lithographically defined superconducting electrodes and graphene layers [4,5,6,7]. In such hybrid devices, a superconducting gap is induced by proximity effect on the graphene region underneath the metallic electrodes;. Study how robust these bound states are to the effect of disorder on the graphene sample. This article is organized as follows: First, we discuss in Section 2 the formation of interface bound states at a graphene-superconductor interface by matching of the solutions of the DBdG equations.

Interface Bound States
Microscopic Model
Effect of Disorder
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