Bilayer quantum Hall system at vt=1: pseudospin models and in-plane magnetic field

We investigate two theoretical pseudomagnon-based models for a bilayer quantum Hall system BQHS at total filling factor t=1. We find a unifying framework which elucidates the different approximations that are made. We also consider the effect of an in-plane magnetic field in BQHSs at t=1, by deriving an equation for the ground-state energy from the underlying microscopic physics. Although this equation is derived for small in-plane fields, its predictions agree with recent experimental findings at stronger in-plane fields, for low electron densities. We also take into account finite-temperature effects by means of a renormalization group analysis, and find that they are small at the temperatures that were investigated experimentally.