Quantum-criticality and superconductivity in twisted transition metal di-chalcogenides

Abstract

We analyze a model for electronic structure and interactions in twisted transition metal chalcogenide WSe$_2$ for superconductivity. In this material, spin-orbit scattering locks the z-components of spins of low-energy fermions near the Dirac ${\bf K}$ and ${\bf K}'$ points of the hexagonal Brillouin zone, reducing the symmetry of spin-spin interactions to that of an xy model. We show that a nominally repulsive 4-fermion interaction gives rise to an attraction for pairing in a two-component $E^{-}$ channel, which is a hexagonal lattice representation of the $\ell =1$ channel. The gap function is inversion-odd and a linear combination of spin singlet and spin triplet. At weak coupling superconductivity emerges via the Kohn-Luttinger mechanism; we compute $T_c$ for the Fermi-level lying close to the van Hove singularity. At strong coupling, the pairing is mediated by XY magnetic fluctuations peaked at momenta ${\bf K}-{\bf K}' = 2 {\bf K}$ and we estimate $T_c$ using the form of the quantum-critical XY fluctuations, displaying $\omega/T$ scaling.