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TT: Fachverband Tiefe Temperaturen

TT 37: Graphene and 2D Materials (joint session TT/HL)

TT 37.5: Talk

Wednesday, March 20, 2024, 10:30–10:45, H 3007

Competing nematic semi-metallic and insulating states in bilayer graphene — •Sebastian Mantilla and Inti Sodemann — Institut für Theoretische Physik, Universität Leipzig, 04107 Leipzig, Germany

The finite density of states arising from the parabolic band touching in ideal Bernal bilayer graphene leads to spontaneous symmetry-breaking instabilities driven by weak repulsive interactions. To this date, different experiments have reported conflicting states, with some reporting a gapped state and others a metallic state that spontaneously breaks lattice rotations. Using a combination of bosonization and self-consistent Hartree-Fock theory, we propose a resolution to these conflicting reports by demonstrating the existence of two closely competing states: a semi-metallic nematic state in which the parabolic band touchings spontaneously split into a pair of linearly dispersing Dirac fermions and a fully gapped state. We find that the gapped state has slightly lower energy, but the energy difference between them is highly sensitive to the interaction strength in a BCS-like fashion. Therefore, in samples with more screening, these states are even closer in energy, and their energetic balance can be tilted by other corrections, such as the trigonal warping, which tends to favour the nematic metallic states.

Keywords: bilayer graphene; nematic phase; weak-coupling instability; bosonization; BCS instability