Enhanced Andreev reflection in gapped graphene

TL;DR

This paper theoretically explores how a band gap in graphene influences the superconducting proximity effect, revealing enhanced Andreev reflection and pseudospin-related phenomena similar to ferromagnetic behavior.

Contribution

It introduces the concept that gapped graphene exhibits ferromagnet-like Andreev reflection properties, expanding understanding of superconducting proximity effects in pseudospin symmetry-broken systems.

Findings

Band gap enhances Andreev conductance in S/PF junctions.

Gapped graphene shows long-range crossed Andreev reflection.

Local density of states exhibits damped-oscillatory behavior.

Abstract

We theoretically demonstrate unusual features of superconducting proximity effect in gapped graphene which presents a pseudospin symmetry-broken ferromagnet with a net pseudomagnetization. We find that the presence of a band gap makes the Andreev conductance of graphene superconductor/pseudoferromagnet (S/PF) junction to behave similar to that of a graphene ferromagnet-superconductor junction. The energy gap $\Delta_N$ enhance the pseudospin inverted Andreev conductance of S/PF junction to reach a limiting maximum value for $\Delta_N\gg \mu$, which depending on the bias voltage can be larger than the value for the corresponding junction with no energy gap. We further demonstrate a damped-oscillatory behavior for the local density of states of the PF region of S/PF junction and a long-range crossed Andreev reflection process in PF/S/PF structure with antiparallel alignment of pseudomagnetizations of PFs, which confirm that, in this respect, the gapped normal graphene behaves like a ferromagnetic graphene.