SKM 2023 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 53: Graphene

TT 53.5: Vortrag

Donnerstag, 30. März 2023, 16:00–16:15, HSZ 204

Twisted bilayer graphene at charge neutrality: Spontaneous symmetry breaking of SU(4) Dirac electrons — •Nikolaos Parthenios and Laura Classen — Max-Planck Institute for Solid State Research, Stuttgart, Germany

We study possible patterns for spontaneous symmetry breaking in twisted bilayer graphene at charge neutrality. Starting from an effective Dirac Hamiltonian, we show how an SU(4) symmetry emerges that is composed of combined spin, valley and sublattice transformations. We construct the corresponding low-energy model that includes all symmetry-allowed four-fermion interactions and employ a renormalization group treatment to identify the critical points that describe transitions into the different ordered phases. The resulting phase diagram depends on the number of fermion flavours and we argue that for twisted bilayer graphene it is governed by a quantum Hall state or SU(4) manifolds of spin-valley orders with emergent Lorentz symmetry. Due to the large symmetry, small perturbations will determine the final symmetry breaking mechanism.