Extended s-wave superconductivity in M-point twisted bilayer SnSe2

Abstract

We investigate the emergence of electronic order and unconventional superconductivity in M-valley moir\'e materials. Starting from a first-principles Wannier model of AB-stacked twisted SnSe2, we tackle the (gate-screened) long-ranged Coulomb interaction with functional renormalization group simulations resolving the momentum structure and energy scales of the leading Fermi surface instabilities. Upon doping an antiferromagnetic stripe state at half-filling ($\nu=3$ electrons per moir\'e unit cell) of the moir\'e flat bands, magnetic order gives way to unconventional superconductivity mediated by valley-selective spin fluctuations: Large hole doping ($\nu\approx1$) leads to weak-coupling superconductors with various pairing symmetries, while slight electron- and hole-doping ($\nu\approx2,4$) stabilizes a spin-singlet, extended s-wave state that benefits from scattering between virtual particle and hole states that are detuned from the Fermi level. These findings establish M-point moir\'e materials as a quantum simulation platform with phenomenological parallels to the class of iron pnictide superconductors.