The enhancement of in-plane H_c2 in monolayer centrosymmetric superconductor 1T^'-WTe₂ via strong spin-orbital coupling

Recently, it was reported that the two-dimensional quantum spin Hall insulator 1T^'-WTe₂ can be gated into the superconducting phase. The in-plane H_c2 in this centrosymmetric superconductor is enhanced up to 2∼4 times Pauli limit. However, unlike the typical enhancement of H_c2 in a non-centrosymmetric superconductor, the mechanism here is not clear. In this work, we find due to the strong spin-orbital coupling (SOC), the spin susceptibility is reduced in the low gating region. In other words, the magnetic field felt by electrons near the Fermi energy is renormalized, which in turn enhances the H_c2. The amplitude of enhancement is comparable to the experiments. Moreover, in this mechanism, the anisotropic SOC will lead to obvious anisotropy in H_c2, which can be tested in experiments by rotating the magnetic field.