| I have adapted the technique of small sample ac calorimetry for a study of the heat capacity at low temperatures of the two-dimensional electron gas (2D EG) in GaAs/Al{dollar}sb{lcub}rm x{rcub}{dollar}Ga{dollar}sb{lcub}rm 1 - x{rcub}{dollar}As multiple quantum well (MQW) structure. In order to minimize relatively large background, calorimetric addenda are directly attached to the bulk substrate supporting a single intact MQW structure. Below 2{dollar}spcirc{dollar}K I observe the 2D EG contribution to the sample heat capacity, in sweeps of magnetic field B, as oscillations periodic in 1/B of relative size 0.1-0.2%. The lineshape of the oscillations is analyzed with reference to theoretical models of the 2D EG density of states (DOS). For samples with both high and low 2D EG densities the experimental lineshape is best modelled by a DOS in which the broadening of Landau levels oscillates as a function of B. In agreement with results from cyclotron-resonance experiments, the broadening attains maxima at B such that the heat capacity is at minima. For samples with low 2D EG densities, I report the first observation in heat capacity data of spin-splitting of 2D EG Landau levels in GaAs/Al{dollar}sb{lcub}rm x{rcub}{dollar}Ga{dollar}sb{lcub}rm 1 - x{rcub}{dollar}As heterostructures. No anomalous features are observed at high B in the FQHE regime. Analysis of the oscillatory lineshape below 10 Tesla implies large enhancement of the spin-splitting g-factor from the zero B value. This is in agreement with results from studies of magnetotransport. |
