Dresden 2017 – scientific programme
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O: Fachverband Oberflächenphysik
O 94: Graphene: Electronic Properties, Structure and Substrate Interaction II
O 94.12: Talk
Thursday, March 23, 2017, 17:45–18:00, TRE Ma
Phase diagram of a graphene bilayer in the zero-energy Landau level — •Angelika Knothe1,2 and Thierry Jolicoeur2 — 1Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg — 2Laboratoire de Physique Théorique et Modèles Statistiques (LPTMS), Université Paris-Sud, 91405 Orsay, France
We theoretically investigate the ground state structure of bilayer graphene (BLG) in the quantum Hall regime. In BLG, the zero energy states carry, besides the real spin, two pseudospin degrees of freedom: a valley isospin and a Landau level (n = 0, n = 1) isospin. This peculiar property leads to an octet of states that is eightfold degenerate in the absence of any symmetry breaking and can be treated in the frame of quantum Hall ferromagnetism. If this SU(8) symmetry is indeed broken, an extraordinary rich phase structure emerges, with each phase characterized by a different spin and isospin configuration. Recent experiments have revealed a plethora of transitions upon variation of the strength of an applied magnetic or electric field. We start from a four-band model Hamiltonian for Bernal stacked BLG and take into account both, intrinsic symmetry breaking effects, as well as the influence of externally applied fields. Using a Hartree-Fock treatment, we study the ground state spin and isospin phases as a function of external magnetic and electric field strengths. For the different filling factors of the zero energy multiplet we predict the number of phases, as well as the nature and the properties of the respective phase transitions.
[1] Angelika Knothe and Thierry Jolicœur, arXiv:1609.04983