Vestigial singlet pairing in a fluctuating magnetic triplet superconductor: Applications to graphene moir\'e systems

TL;DR

This paper investigates a 2D model inspired by graphene moiré superlattices, revealing vestigial phases with unique properties like charge-4e superconductivity and broken time-reversal symmetry, which may explain experimental observations.

Contribution

It introduces a novel phase with finite   N, exhibiting properties similar to BCS superconductivity but with distinct spectral features, advancing understanding of complex superconducting states.

Findings

Identification of vestigial phases including charge-4e superconductivity

Discovery of a phase with   N symmetry and Meissner effect

Spectral suppression resembling gapped or nodal superconductors

Abstract

Motivated by the phenomenology of graphene moir\'e superlattices, we study a 2D model with strong tendencies towards both magnetism and triplet superconductivity. Individually, their respective order parameters, $\vec{N}$ and $\vec{d}$, cannot order at finite temperature. Nonetheless, the model exhibits a variety of vestigial phases, including charge-$4e$ superconductivity and broken time-reversal symmetry. Our main focus is on a phase characterized by finite $\vec{d} \cdot \vec{N}$, which has the same symmetries as the BCS state, a Meissner effect, and metastable supercurrents, yet rather different spectral properties: most notably, the suppression of the electronic density of states at the Fermi can resemble that of either a fully gapped or nodal superconductor, depending on parameters. This could provide a possible explanation for recent tunneling experiments in graphene moir\'e systems.