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

TL;DR

This paper explores how valley contrasting flux influences superconductivity in a t-J model on a triangular moiré lattice, revealing topological phase transitions and novel pairing symmetries relevant to twisted TMD heterobilayers.

Contribution

It introduces a slave boson mean field analysis of the t-J model with valley contrasting flux, uncovering new topological phases and pairing symmetries in moiré TMD systems.

Findings

Finite flux breaks spin rotation symmetry and induces mixed pairing states.

Identification of two topological phase transitions with Dirac nodes.

Small anisotropy can lead to time reversal invariant nodal superconductivity.

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.