Tunneling conductance in $s$- and d-wave superconductor-graphene junctions: Extended Blonder-Tinkham-Klapwijk formalism

TL;DR

This paper analyzes the conductance spectra of graphene-superconductor junctions with s-wave and d-wave pairing, using an extended BTK formalism to explore the full crossover from normal to specular Andreev reflection and effects of unconventional pairing.

Contribution

It extends the BTK formalism to include both s-wave and d-wave pairings in graphene junctions, covering the full Andreev reflection crossover without approximations.

Findings

Conductance spectra are significantly affected by pairing symmetry.

Unconventional d-wave pairing induces distinct conductance features.

Analytical and numerical results clarify conductance oscillations in junctions.

Abstract

We investigate the conductance spectra of a normal/superconductor graphene junction using the extended Blonder-Tinkham-Klapwijk formalism, considering pairing potentials that are both conventional (isotropic s-wave) and unconventional (anisotropic d-wave). In particular, we study the full crossover from normal to specular Andreev reflection without restricting ourselves to special limits and approximations, thus expanding results obtained in previous work. In addition, we investigate in detail how the conductance spectra are affected if it is possible to induce an unconventional pairing symmetry in graphene, for instance a d-wave order parameter. We also discuss the recently reported conductance-oscillations that take place in normal/superconductor graphene junctions, providing both analytical and numerical results.