Pair density wave and reentrant superconducting tendencies originating from valley polarization

TL;DR

This paper explores how valley polarization in a 2D electron system can induce exotic superconducting states, including pair-density-wave order and re-entrant superconductivity, with potential relevance to twisted graphene experiments.

Contribution

It demonstrates that spontaneous valley polarization can lead to unconventional superconducting tendencies, a novel insight into the interplay between valley degrees of freedom and superconductivity.

Findings

Valley polarization can induce singlet pair-density-wave order.

Re-entrant superconductivity occurs at high magnetic fields.

Reduced magnetic response allows violation of the Pauli limit.

Abstract

We investigate superconducting pairing tendencies of a two-dimensional electron fluid with both valley and spin degrees of freedom, both without and in the presence of an in-plane magnetic field. We present suggestive theoretical arguments that spontaneous valley polarization can lead to exotic singlet superconducting tendencies, including pair-density-wave order at zero field and re-entrant superconductivity at high field. We also find a reduced magnetic response in the polarized valley, which allows a finite violation of the Pauli limit. These results are obtained by a mean-field approach to a generalized $t$-$J$ model on a triangular lattice and in the dilute limit. Phenomenological similarities to results of recent magic-angle twisted trilayer graphene experiments are noted.