Regensburg 2022 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 21: Correlated Electrons: Poster Session
TT 21.27: Poster
Wednesday, September 7, 2022, 15:00–18:00, P1
Chern insulators in twisted bilayer graphene under hydrostatic pressure — •Israel Díaz1, José González2, and Tobias Stauber1 — 1Materials Science Factory, Instituto de Ciencia de Materiales de Madrid, CSIC, E-28049, Madrid, Spain — 2Instituto de Estructura de la Materia, CSIC, E-28006, Madrid, Spain
It is well-known that high hydrostatic pressures can be used to induce flat bands in twisted bilayer graphene, at twist angles larger than those realizing the usual magic-angle condition. We show that these twisted graphene bilayers, tuned at such larger magic angles, are prone to fall into Chern insulator phases. We characterize such states by relying on a self-consistent real-space Hartree-Fock approach that accounts for the long-range Coulomb interaction between all the carbon atoms in the moiré unit cell, and which is exact at the Hartree-Fock level as we incorporate all the moiré minibands in the calculation. In our flat-band models with twist angles between 2 and 4 degrees, we show that a gap opens up at the charge neutrality point due to the dynamical breakdown of time-reversal invariance. At 2 hole-doping, the dominant order parameter corresponds instead to valley symmetry breaking, but there is a critical coupling of the interaction above which a gap opens up due to the condensation of the Haldane mass. These Chern insulator phases seem to be absent in twisted bilayer graphene at the usual small magic angle, probably because they are hindered by the effects of in-plane relaxation, but they become manifest at the larger twist angles we study, leading to interesting phenomena like dissipationless edge states and anomalous Hall effect.