HEAT-CAPACITY AND NUCLEAR-SPIN DYNAMICS IN GAAS ALGAAS HETEROSTRUCTURES AROUND NU=1/

We report low-temperature (T) heat capacity (C) data on a multiple-qua ntum-well GaAs/AlGaAs sample in the quantum Hall regime. Relative to i ts low field magnitude, C exhibits up to approximate to 10(5)-fold enh ancement near Landau level filling v = 1. We attribute this striking b ehavior 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 pe ak suggestive of a phase transition in the electronic system. Quasi-ad iabatic experiments provide quantitative evidence that the sharp peak in C versus T is due to an enhanced nuclear-spin diffusion from the Ga As quantum wells into the AlGaAs barriers. (C) 1998 Elsevier Science B .V. All rights reserved.