Dresden 2017 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 74: Graphene: Electronic Properties, Structure and Substrate Interaction II (joint session DY, DS, HL, MA, O, TT, organized by O)

TT 74.12: Talk

Thursday, March 23, 2017, 17:45–18:00, TRE Ma

Phase diagram of a graphene bilayer in the zero-energy Landau level — •Angelika Knothe^1,2 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