Finite-temperature transitions in nu=2 bilayer quantum Hall systems

In this paper, the influence of an in-plane magnetic field B-parallel to on the transitions at finite temperatures in v = 2 bilayer quantum Hall syste ms is examined. It is found that there can exist two types of characteristi c temperatures which separate different regions in the phase diagram. The f irst is the Kosterlitz-Thouless (KT) transition temperature, which can have an unusual nonmonotonic dependence on B-parallel to; the second type origi nates from the crossing of energy levels and always increases with B-parall el to. Based on these results, we point out that the threshold temperature observed in the inelastic light scattering experiments cannot be the KT tra nsition temperature, because the latter shows a totally different B-paralle l to dependence as compared with the experimental observation. Instead, it should be the level-crossing temperature, which we found agrees with the B- parallel to dependence observed. Thus an investigation of the KT transition in the bilayer quantum Hall systems awaits experimental measurements to pr obe the proposed canted antiferromagnetic phase more directly.