Spin-orbit-parity coupled superconductivity in topological monolayer WTe2
Abstract
Recent experiments reported gate-induced superconductivity in the monolayer 1T'-WTe2 which is a two-dimensional topological insulator in its normal state [1, 2]. The in-plane upper critical field Bc2 is found to exceed the conventional Pauli paramagnetic limit Bp by 1-3 times. The enhancement cannot be explained by conventional spin-orbit coupling which vanishes due to inversion symmetry. In this work, we unveil some distinctive superconducting properties of centrosymmetric 1T'-WTe2 which arise from the coupling of spin, momentum and band parity degrees of freedom. As a result of this spin-orbit-parity coupling: (i) there is a first-order superconductor-metal transition at Bc2 much higher than the Pauli paramagnetic limit Bp, (ii) spin-susceptibility is anisotropic with respect to in-plane directions and results in anisotropic Bc2 and (iii) the Bc2 exhibits a strong gate dependence as the spin-orbit-parity coupling is significant only near the topological band crossing points. The importance of SOPC on the topologically nontrivial inter-orbital pairing phase is also discussed. Our theory generally applies to centrosymmetric materials with topological band inversions.