Andreev reflection tuned by magnetic barriers in superconductor contacted graphene

TL;DR

This paper investigates how magnetic barriers influence Andreev reflection in graphene-superconductor junctions, revealing tunable reflection angles, enhanced specular reflection, and complex resonance phenomena in monolayer and bilayer graphene.

Contribution

It introduces a detailed analysis of magnetic barrier effects on Andreev reflection in graphene-superconductor interfaces using Green's function formalism.

Findings

Magnetic barriers can tune the angles of Andreev reflection.

Enhanced specular reflection probability at certain angles.

Presence of Fano resonances and Fabry-Pérot oscillations in the reflection spectra.

Abstract

The Andreev reflection of the normal state-superconductor junction both in monolayer and bilayer graphene with a single magnetic barrier is investigated by means of the Green's function formalism. Within the tight-binding model, we study the direction-dependent Andreev reflection of two-dimensional graphene-superconductor junctions in the specular and retro-reflection regimes. The presence of a magnetic barrier close to the superconducting hybrid junction introduces a rich phenomenology. Such a barrier is capable of tuning the preferred angles of incidence for the Andreev reflection. In particular, it can enhance the specular reflection probability for certain angles of incidence in bilayer-based hybrid structures. When transmission is permitted, the Andreev reflection manifests itself in isolated peaks and asymmetric resonances associated with offsets and Fano-type oscillations in the transmission, respectively. Moreover, Fabry-P\'{e}rot oscillations in the Andreev reflection due to the interior scattering inside the magnetic barrier may appear. The impacts of magnetic barriers on the monolayer and bilayer hybrid interfaces are furthermore studied by calculating the differential conductances within the Blonder-Tinkham-Klapwijk formula.