CPM Seminar

Bilayer quantum Hall excitons: evidence for a finite temperature phase transition

Alexandre Champagne

Concordia University

When the separation between two parallel 2D electron systems becomes comparable to the average distance between electrons within a single layer, the system can support a strongly correlated phase at total filling factor ν_T= 1. This phase exhibits a spontaneous interlayer phase coherence which may be described as an excitonic Bose condensate. We study the Joshepson-like interlayer tunneling signature of this state as a function of the effective separation between the two layers, the interlayer charge imbalance, and temperature. The interlayer tunneling amplitude dependence on the layer spacing at various temperatures obeys an empirical power law scaling, and the layer separation where the tunneling disappears scales linearly with temperature. Our results offer evidence [1] that a finite temperature phase transition, a first in a quantum Hall system, separates the interlayer excitonic phase from incoherent phases which lack strong interlayer correlations. We also report [2] the first observation of a direct phase transition between the coherent excitonic bilayer integer quantum Hall phase and a pair of single layer fractional quantized Hall states at ν = (2/3, 1/3).

[1] A.R. Champagne, et al., Phys. Rev. Lett. 100, 096801 (2008).
[2] A.R. Champagne, et al., arXiv:0808.1257.