GIANT LOW-TEMPERATURE HEAT-CAPACITY OF GAAS QUANTUM-WELLS NEAR LANDAU-LEVEL FILLING 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 similar to 10(5)-fold enhance ment near v = 1 where Skyrmions are the ground state of the confined t wo-dimensional electrons. We attribute the large C to a Skyrmion-induc ed, strong coupling of the nuclear spin system to the lattice. The dat a 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 elec tronic system.