Energy relaxation in a low-density nonequilibrium 2D hole gas at the quantum hall plateau-plateau transition

We have measured the derivative S = dR_xy/dB of the transverse resistance R_xy vs magnetic field B at the ν=3 -> ν=2 (B=0.45 T) quantum Hall plateau-plateau transition (PPT) , as function of the sample temperature T and dissipated Joule’s power P in a low-density, p-doped GaAs/AlGaAs quantum well with a high interaction parameter r_s ~ 23 (n_h= 2.9 x 10¹⁰ /cm^-2, hole mobility μ = 2.4 x 10⁵ cm²/Vs). We present P-T curves constructed by matching P and T values at a given S, and compare these to a set of similar curves obtained for the sample resistance R at B=0. At low temperatures, the P-T data in the magnetic field and at B=0 diverge suggesting that the thermal coupling between the holes and the lattice increases in the magnetic field and makes the holes effectively cooler at a given P. We also find that the thermal coupling in the magnetic field shows a weaker temperature dependence than at B=0. We compare these findings to an earlier work on a system with a lower r_s=2.17 [1] and discuss possible nonlinear effects near the PPT under conditions of electric current flow. [1] Edmond Chow, H. P. Wei, S. M. Girvin, and M. Shayegan. Phys. Rev. Lett., 1996. Vol. 77(6), pp 1143-1146.