Landau level degeneracy in twisted bilayer graphene: Role of symmetry breaking

Abstract

The degeneracy of Landau levels flanking charge neutrality in twisted bilayer graphene is known to change from eightfold to fourfold when the twist angle is reduced to values near the magic angle of $\ensuremath{\approx}1.{05}^{\ensuremath{\circ}}$. This degeneracy lifting has been reproduced in experiments by multiple groups and is known to occur even in devices which do not harbor the correlated insulators and superconductors. We propose ${C}_{3}$-symmetry breaking as an explanation of such robust degeneracy lifting and support our proposal by numerical results on the Landau-level spectrum in near-magic-angle twisted bilayer graphene. Motivated by recent experiments, we further consider the effect of ${C}_{2}$-symmetry breaking on the Landau levels.