Heat capacity and nuclear-spin dynamics in GaAs/AlGaAs heterostructures around v = 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. 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 versus T exhibits a remarkably sharp peak suggestive of a phase transition in the electronic system. Quasi-adiabatic experiments provide quantitative evidence that the sharp peak in C versus T is due to an enhanced nuclear-spin diffusion from the GaAs quantum wells into the AlGaAs barriers.