Superconducting proximity effect in graphene under inhomogeneous strain

TL;DR

This paper investigates how inhomogeneous strain in graphene affects superconducting proximity effects, revealing regimes where supercurrent is enhanced or suppressed, and uncovering strain-induced edge states and polarization effects.

Contribution

It introduces a novel analysis of superconducting proximity in strained graphene, including the effects of pseudo-magnetic fields and the extension of computational methods to GPUs.

Findings

Supercurrent can be enhanced or suppressed depending on the strain regime.

Strain induces sub-lattice polarization of pair correlations.

Quantized Hall states and edge states emerge due to strain.

Abstract

The interplay between quantum Hall states and Cooper pairs is usually hindered by the suppression of the superconducting state due to the strong magnetic fields needed to observe the quantum Hall effect. From this point of view graphene is special since it allows the creation of strong pseudo-magnetic fields due to strain. We show that in a Josephson junction made of strained graphene, Cooper pairs will diffuse into the strained region. The pair correlation function will be sub-lattice polarized due to the polarization of the local density of states in the zero pseudo-Landau level. We uncover two regimes; 1) one in which the cyclotron radius is larger than the junction length in which case the supercurrent will be enhanced, and 2) the long junction regime where the supercurrent is strongly suppressed because the junction becomes an insulator. In the latter case quantized Hall states form and Andreev scattering at the normal/superconducting interface will induce edge states. Our numerical calculation has become possible due to an extension of the Chebyshev Bogoliubov-de Gennes method to computations on video cards (GPUs).