Heat capacity of a 2DEG

We review recent heat capacity experiments performed on GaAs/AlGaAs heterostructures containing two-dimensional electron layers. Near v=1, the strong coupling to the nuclear spin system attributed to Skyrmion-induced low-energy spin excitations has a dramatic effect on the heat capacity which rises by orders of magnitude. We show that this giant heat capacity is consistent with the Schottky nuclear heat capacity of Ga and As atoms in the quantum wells, except at very low temperature where heat capacity exhibits a remarkably sharp peak suggestive of a phase transition in the electronic system. We also report quasi-adiabatic experiments providing quantitative evidence that the sharp peak in heat capacity is due to an enhanced nuclear-spin diffusion from the GaAs quantum wells into the AlGaAs barriers. Finally, we present the latest heat capacity results which probe the presence or the absence of Skyrmions at large Zeeman energy. (C) 1998 Elsevier Science B.V. All rights reserved.