Subgap states in two dimensional spectroscopy of unconventional superconductors using graphene

TL;DR

This paper investigates how graphene's unique two-dimensional properties influence the transport and spectral features of proximity-induced unconventional superconductivity, highlighting the roles of edge states, interface states, and resonances.

Contribution

It provides a microscopic analytical framework to distinguish contributions of various subgap states in graphene-superconductor junctions, aiding experimental identification of pairing symmetry.

Findings

Edge states and interface bound states significantly affect conductance.

Finite size induces Fabry-Pérot resonances impacting spectral density.

Graphene can help determine the pairing symmetry of unconventional superconductors.

Abstract

The two-dimensional nature of graphene makes it an ideal platform to explore proximity-induced unconventional planar superconductivity and the possibility of topological superconductivity. Using Green's functions techniques, we study the transport properties of a finite size ballistic graphene layer placed between a normal state electrode and a graphene lead with proximity-induced unconventional superconductivity. Our microscopic description of such a junction allows us to consider the effect of edge states in the graphene layer and the imperfect coupling to the electrodes. The tunnel conductance through the junction and the spectral density of states feature a rich interplay between graphene's edge states, interface bound states formed at the graphene-superconductor junction, Fabry-P\'erot resonances originated from the finite size of the graphene layer, and the characteristic Andreev surface states of unconventional superconductors. Within our analytical formalism, we identify the separate contribution from each of these subgap states to the conductance and density of states. Our results show that graphene provides an advisable tool to determine experimentally the pairing symmetry of proximity-induced unconventional superconductivity.