Josephson junctions of topological nodal superconductors

TL;DR

This paper investigates the unique current-phase relation in Josephson junctions of topological nodal superconductors derived from monolayer TMDs, revealing $4\pi$ periodicity and topological phase transitions related to Majorana flat bands.

Contribution

It provides a detailed analysis of the energy-phase relation and topological phases in Josephson junctions of topological nodal superconductors, highlighting the role of transverse momentum and quantum phase transitions.

Findings

Energy-phase relation depends on transverse momentum.

Identifies $4\pi$ periodicity between nodal points.

Topological phase transitions driven by transverse momentum.

Abstract

Transition metal dichalcogenides (TMDs) offer a unique platform to study unconventional superconductivity, owing to the presence of strong spin-orbit coupling and a remarkable stability to an in-plane magnetic field. A recent study found that when an in-plane field applied to a superconducting monolayer TMD is increased beyond the Pauli critical limit, a quantum phase transition occurs into a topological nodal superconducting phase which hosts Majorana flat bands. We study the current-phase relation of this nodal superconductor in a Josephson junction geometry. We find that the nodal superconductivity is associated with an energy-phase relation that depends on the momentum transverse to the current direction, with a $4\pi$ periodicity in between pairs of nodal points. We interpret this response as a result of a series of quantum phase transitions, driven by the transverse momentum, which separate a topological trivial phase and two distinct topologically non-trivial phases characterized by different winding invariants. This analysis sheds light on the stability of the Majorana flat bands to symmetry-breaking perturbations.