Giant heat capacity and nuclear-spin diffusion in GaAs/AlGaAs heterostructures near ν=1

We report low temperature (T) heat capacity (C) data on a multiple-quantum-well GaAs/AlGaAs sample in the quantum-Hall regime. Relative to its low field magnitude, C exhibits up to ≈10⁵-fold enhancement near Landau level filling v=1 where skyrmions are the expected ground state of the confined two-dimensional electrons. We attribute this striking behavior to a skyrmion-induced enhancement of the coupling between the nuclear spin system and the lattice. The data are consistent with the Schottky nuclear heat capacity of Ga and As atoms in the quantum wells, except at very low T where C vs. T exhibits a remarkably sharp peak suggestive of a phase transition in the electronic system. Our quasi-adiabatic experiments provide quantitative evidence that the sharp peak in C vs. T is due to an enhanced nuclear-spin diffusion from the GaAs quantum wells into the AlGaAs barriers. We discuss the physical origin of this enhancement in terms of the possible Skyrme solid–liquid phase transition.