The Mott-semiconducting state in the magic angle bilayer graphene

Abstract

Using non-perturbative theoretical method, we address the problem of strong correlations in twisted bilayer-layer graphene at the magic angle. We concentrate on the solution without symmetry breaking, where conventional Mott insulating state is expected for all integer fillings. At Coulomb repulsion corresponding to dielectric constant $\varepsilon\approx 5$ and several integer fillings we find a Mott-semiconducting state, which simultaneously hosts the Mott state, and inside the Mott gap, a second much smaller semiconduting gap. The presence of these Mott-ingap states, which are located at the $\Gamma$ point, makes the Mott state strongly temperature dependent and leads to a bad-metal phase at elevated temperatures. The system is insulating at the charge neutrality point and at even fillings away from it.