Unexpected two-fold symmetric superconductivity in few-layer NbSe2*

Transition metal dichalcogenides (TMDs) have attracted significant interest due to properties such as layer-dependent inversion symmetry, valley-contrasted Berry curvatures, and strong spin-orbit coupling (SOC). Few-layer niobium diselenide (NbSe2) exhibits Ising SOC, which helps stabilize the superconducting state and could lead to exotic properties such as topological superconductivity. Here, we report transport measurements of few-layer NbSe2 under in-plane external magnetic fields. In contrast to the three-fold symmetry of the lattice, we observe the magnetoresistance, critical field, and differential conductance measurements all exhibit a two-fold oscillation confined to the superconducting phase. We attribute the behavior to the mixing between two closely competing pairing instabilities. Our results demonstrate the unconventional character of the pairing interaction in a few-layer TMD, opening a new avenue to search for exotic superconductivity in this family of 2D materials.

arXiv:2004.02999