Global phase diagram of v = 2 quantum Hall bilayers in tilted magnetic fields

Abstract

We consider a bilayer quantum Hall system at total filling fraction n=2 in tilted magnetic field allowing for charge imbalance as well as tunneling between the two layers. Using an “unrestricted Hartree Fock,” previously discussed by Burkov and MacDonald [Phys. Rev. B 66, 115323 (2002)], we examine the zero temperature global phase diagrams that would be accessed experimentally by changing the in-plane field and the bias voltage between the layers while keeping the tunneling between the two layers fixed. In accordance with previous work, we find symmetric and ferromagnetic phases as well as a first-order transition between two canted phases with spontaneously broken U(1) symmetry. We find that these two canted phases are topologically connected in the phase diagram and, reminiscent of a first-order liquid-gas transition, the first-order transition line between these two phases ends in a quantum critical point. We develop a physical picture of these two phases and describe in detail the physics of the transition.