Ising pairing in superconducting NbSe2 atomic layers (Englisch)

The properties of two-dimensional transition metal dichalcogenides arising from strong spinorbit interactions and valley-dependent Berry curvature effects have recently attracted considerable interest17. Although single-particle and excitonic phenomena related to spinvalley coupling have been extensively studied1,36, the eects of spinvalley coupling on collective quantum phenomena remain less well understood. Here we report the observation of superconducting monolayer NbSe2 with an in-plane upper critical eld of more than six times the Pauli paramagnetic limit, by means of magnetotransport measurements. The ffeect can be interpreted in terms of the competing Zeeman eect and large intrinsic spinorbit interactions in non-centrosymmetric NbSe2 monolayers, where the electron spin is locked to the out-of-plane direction. Our results provide strong evidence of unconventional Ising pairing protected by spinmomentum locking, and suggest further studies of non-centrosymmetric superconductivity with unique spin and valley degrees of freedom in the two-dimensional limit.