Proximity-driven ferromagnetism and superconductivity in the triangular Rashba-Hubbard model

TL;DR

This paper explores how Rashba spin-orbit coupling in a triangular lattice Hubbard model influences ferromagnetism and superconductivity, revealing the potential for chiral triplet pairing and mixed parity states, relevant for twisted bilayer materials.

Contribution

It demonstrates that Rashba spin-orbit coupling promotes ferromagnetic fluctuations and triplet superconductivity, including chiral states, in a triangular lattice Hubbard model, with implications for Moiré materials.

Findings

Rashba coupling favors ferromagnetic fluctuations.

Triplet (p-wave) superconductivity is strengthened.

Time-reversal symmetry breaking leads to chiral states.

Abstract

Bilayer Moir\'e structures are a highly tunable laboratory to investigate the physics of strongly correlated electron systems. Moir\'e transition metal dichalcogenides at low-energies, in particular, are believed to be described by a single narrow band Hubbard model on a triangular lattice with spin-orbit coupling. Motivated by recent experimental evidence for superconductivity in twisted bilayer materials, we investigate the possible superconducting pairings in a two-dimensional single band Rashba-Hubbard model. Using a random-phase approximation in the presence of nearest and next-nearest neighbor hopping, we analyze the structure of spin fluctuations and the symmetry of the superconducting gap function. We show that Rashba spin-orbit coupling favors ferromagnetic fluctuations which strengthen triplet superconductivity. If parity is violated due to the absence of spatial inversion symmetry, singlet (d-wave) and triplet (p-wave) channels of superconductivity will be mixed. Moreover, we show that time-reversal symmetry can be spontaneously broken leading to a chiral superconducting state. Finally, we consider quasiparticle interference as a possible experimental technique to observe the superconducting gap symmetry.