Prediction of novel `magic' angles and correlations for twisted bilayer graphene in a perpendicular electric field

TL;DR

This paper identifies new exactly solvable 'magic' angles in twisted bilayer graphene under a perpendicular electric field, revealing flat bands and strong correlations at multicritical Lifshitz points, advancing understanding of correlated phases.

Contribution

It introduces a novel set of 'magic' angles with exact solutions, highlighting the role of electric fields and Lifshitz points in flat band formation and correlations.

Findings

Discovery of new 'magic' angles with exact solutions.

Presence of monkey saddle in the central band at these angles.

Strong electronic correlations at multicritical Lifshitz points.

Abstract

At certain angles of rotation called `magic angles' twisted bilayer graphene features almost flat bands. The resulting strong correlations drive the system to novel phases which have been observed in experiments recently. A complete understanding of the `magic' angle physics---both at the single-particle as well as the many-particle level---is still missing, and the search is ongoing. Here, we identify a new set of `magic' angles, where locally flat bands with a variety of possible many-body instabilities arise, but where the single-particle problem admits an exact solution. This occurs in the presence of an external perpendicular electric field at multicritical Lifshitz points. At these angles, which can be quantified exactly, the central band features a monkey saddle, resulting in strong electronic correlations.