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Seminar Theory: Friday, 1st December 2023 at 11:00 am

Glenn Wagner (Zürich University)

Title: How strain and phonons modify the strong-coupling picture of twisted bilayer graphene

LPMMC, Room G421


Abstract: The strong coupling picture of twisted bilayer graphene provides a framework for understanding the correlated insulators observed in experiments. In this picture, the insulators are generalised quantum Hall ferromagnets which break certain symmetries. However, this picture is known to be incomplete and certain features are incompatible with experiments. In particular, recent scanning tunnelling have observed a state that breaks moiré translational symmetry. I will show that incorporating strain into a Hartree-Fock study of twisted bilayer graphene results in precisely the state observed in experiment. On the other hand, a state that respects moiré translational symmetry has been observed in low strain devices. Reconciling this observation with the model requires an additional ingredient, namely a specific phonon mode, the so-called K-phonon. I will investigate whether this phonon mode could be responsible for superconductivity.