Enhanced thermal activation in the flanks the ν = 1 integer quantum Hall plateau

In the region of the nu=1 quantized Hall plateau of two-dimensional electron gases of modest quality transport is activated, and the activation energy monotonically decreases with an increasing quasiparticle density. We found that in some of the highest mobility electron gases confined to GaAs/AlGaAs quantum wells transport along the nu=1 plateau is activated as well. However, in contrast low mobility samples, the activation energy in high quality electron gases is non-monotonic with the quasiparticle density. We find that in the flanks of the nu=1 plateau the activation energy is enhanced. Furthermore, the non-monotonic dependence of the activation energy on the quasiparticle density correlates with the regions of single particle localization and collective pinning. Indeed, the activation energy reaches local maxima in the middle of the single particle localization and the collective pinning regimes. In addition, we find that at the boundary of single and collective localization regimes the activation anergy has a conspicuous local minimum. Our results determine the thermodynamic properties of the two-dimensional electron gas and constrain the theory describing the transition between single particle localization and collective pinning.