Séminaire Dganit MEIDAN

Jeudi 3 octobre 2024, 14h00, salle E4.13b

Dganit MEIDAN

Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides.

Josephson junctions of topological nodal superconductors 

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. We futher analyze the effect of Rashba spin orbit coupling on the nodal SC phase. Generically, Rashba spin-orbit is known to lift the chiral symmetry that protects the nodal points, resulting in a fully gapped phase. However, when the magnetic field is applied along the $\Gamma -K $ line, a residual vertical mirror symmetry protects a nodal crystalline phase. We show that while the resulting nodal crystalline phase is characterized by localized edge modes, the current phase relation exhibits a trivial $2\pi $ periodicity in the presence of Rashba spin-orbit coupling

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