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

TL;DR

This paper investigates how in-plane magnetic fields affect finite-temperature phase transitions in nu=2 bilayer quantum Hall systems, identifying two types of transitions and clarifying their experimental signatures.

Contribution

It distinguishes between Kosterlitz-Thouless and level-crossing transitions, providing a detailed phase diagram and clarifying experimental observations.

Findings

KT transition temperature has a non-monotonic B_ dependence

Level-crossing transition temperature increases with B_

Experimental threshold temperature matches level-crossing transition

Abstract

In this paper, the influence of an in-plane magnetic field B_\parallel on the finite-temperature phase transitions in nu=2 bilayer quantum Hall systems are examined. It is found that there can exist two types of finite-temperature phase transitions. The first is the Kosterlitz-Thouless (KT) transitions, which can have an unusual non-monotonic dependence on B_\parallel; the second type originates from the crossing of energy levels and always increases with B_\parallel. Based on these results, we point out that the threshold temperature observed in the inelastic light scattering experiments cannot be the KT transition temperature, because the latter shows a totally different B_\parallel-dependence as compared with the experimental observation. Instead, it should be the level-crossing temperature, which we found agrees with the B_\parallel-dependence observed. Moreover, combining the knowledge of these two transition temperatures, a complete finite-temperature phase diagram is presented.