Ising superconductivity in NbSe_2-xTe_x with tunable spin-orbit coupling

The Ising superconductors of monolayered transition metal dichalcogenides such as MoS₂ and NbSe₂ have been shown to possess strongly enhanced upper critical fields. In these systems, the spin-orbit coupling (SOC) pins the electron spins to the out-of-plane direction because of in-plane mirror symmetry breaking, thereby becoming insensitive to the lateral external magnetic fields. Here, using first-principles density functional theory calculations, we demonstrate that the Te substitution of Se in NbSe₂ will enhance the strength of the SOC, as characterized by the increased spin splitting in the electronic structures of NbSe_2-xTe_x. As a consequence, the upper critical fields of these systems will be further enhanced. Moreover, as x approaches to 2, the enhanced SOC leads to a band inversion around the high symmetry M point in the Brillouin zone, indicating a quantum phase transition towards a topological superconducting state.