Superconductivity, correlated insulators, and Wess-Zumino-Witten terms in twisted bilayer graphene

TL;DR

This paper explores the interplay of superconductivity and correlated insulators in twisted bilayer graphene, proposing Wess-Zumino-Witten terms as a unifying framework linking different orders and their defects.

Contribution

It introduces a novel theoretical framework connecting superconductivity and correlated insulators via Wess-Zumino-Witten terms in twisted bilayer graphene.

Findings

Defects of one order contain quanta of another.

Skyrmion fluctuations may mediate superconductivity.

Comprehensive list of plausible low-temperature orders.

Abstract

Recent experiments on twisted bilayer graphene have shown a high-temperature parent state with massless Dirac fermions and broken electronic flavor symmetry; superconductivity and correlated insulators emerge from this parent state at lower temperatures. We propose that the superconducting and correlated insulating orders are connected by Wess-Zumino-Witten terms, so that defects of one order contain quanta of another order and skyrmion fluctuations of the correlated insulator are a "mechanism" for superconductivity. We present a comprehensive listing of plausible low-temperature orders, and the parent flavor symmetry breaking orders. The previously characterized topological nature of the band structure of twisted bilayer graphene plays an important role in this analysis.