1203.6340 (Bitan Roy)

Theory of integer quantum Hall effect in bilayer graphene near
neutrality point    [PDF]

Bitan Roy

A Hartree-Fock variational ground state for dual-gated bilayer graphene (BLG) in the presence of magnetic fields is proposed. We argue that near the charge neutrality point (CNP), a Neel as well as uniform magnetization can coexist in the presence of the magnetic fields. An infinitesimal Zeeman coupling restricts the Neel order to the easy plane and develops magnetization in the direction of the field. Many-body effects further enhance the size of the magnetization. Such interaction induced gap near the CNP displays a quadratic dependence with the field, when it is weak. It then crosses over to a linear one at intermediate strength of the field, and possibly persisting even at stronger fields. These features are in qualitative accordance with a recent experimental observation. Furthermore, with realistic strengths of the interactions, we establish an quantitative agreement with experiment for 0 T < B < 4.5 T. Upon tilting the field, the Neel order gradually vanishes and a pure ferromagnetic order emerges beyond a critical strength of the total field, which otherwise depends monotonically on its perpendicular component and the zero field gap. Formation of additional incompressible Hall states and the nature of the broken symmetry phases at other fillings, e.g., $\nu=\pm 2$, are discussed as well.

View original: http://arxiv.org/abs/1203.6340