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 4π 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 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.
Bibliographical noteFunding Information:
The authors would like to thank Beena Kalisky, Amit Keren and Binghai Yan for fruitful discussions. D.M. acknowledges support from the Israel Science Foundation (ISF) (grant No. 1884/18). M.K. and D.M. acknowledge support from the ISF, (grant No. 1251/19).
Copyright R. Seshadri et al. This work is licensed under the Creative Commons Attribution 4.0 International License. Published by the SciPost Foundation.