Chiral and nodal superconductors in t-J model with valley contrasting flux on triangular moir\'e lattice

Abstract

Recent experimental progresses have made it possible to simulate spin 1/2 Hubbard model on triangular lattice in moir\'e materials formed by transition metal dichalcogenide (TMD) heterobilayer or homobilayer. In twisted TMD homobilayer, a vertical electric field can induce a valley contrasting flux in the hopping term. In this paper we study possible superconductors from a t-J model with valley contrasting flux $\Phi$ using the slave boson mean field theory. We obtain a phase diagram with doping $x$ and $\Phi$. A finite $\Phi$ breaks spin rotation symmetry and the pairing symmetry is a superposition of spin singlet $d-id$ and spin triplet $p+ip$. There are two topological phase transitions when tuning $\Phi$ from $0$ to $\pi$, with three Dirac nodes at one transition and one single Dirac node at the other transition. We also discuss the effects of van Hove singularity and a three-site correlated hopping term on the pairing strength. Lastly, we demonstrate that a small anisotropy term breaking the $C_3$ rotation can lead to a time reversal invariant nodal superconductor connected to the $d_{x^2-y^2}$ superconductor on square lattice.