Probing the order parameter symmetry of two-dimensional superconductors by twisted Josephson interferometry

TL;DR

This paper proposes a method using twisted Josephson junctions to determine the symmetry of the superconducting order parameter in two-dimensional materials, aiding understanding of unconventional superconductivity.

Contribution

It introduces a general experimental setup for probing order parameter symmetry in 2D superconductors using twist angle dependence in Josephson junctions, with a specific example involving NbSe2 and twisted bilayer graphene.

Findings

Critical current varies with twist angle depending on order parameter symmetry.

Distinct signatures in current-phase relations reveal different symmetries.

Magnetic field dependence provides additional symmetry information.

Abstract

Probing the superconducting order parameter symmetry is a crucial step towards understanding the pairing mechanism in unconventional superconductors. Inspired by the recent discoveries of superconductivity in various van der Waals materials, and the availability of the relative twist angle as a continuous tuning knob in these systems, we propose a general setup for probing the order parameter symmetry of two-dimensional superconductors in twisted Josephson junctions. The junction is composed of an anisotropic s-wave superconductor as a probe and another superconductor with an unknown order parameter symmetry. Assuming momentum-resolved tunneling, we investigate signatures of different order parameter symmetries in the twist angle dependence of the critical current, the current-phase relations, and magnetic field dependence. As a concrete example, we study a twisted Josephson junction between NbSe2 and magic angle twisted bilayer graphene.