Thermodynamics of a charged fermion layer at high r_s values

The chemical potential μ of a hole layer is mapped as a function of temperature and density p. We present the first investigation of the crossover from the strongly interacting degenerate regime to the classical ideal gas limit. The low temperature inverse compressibility, κ-1 ≡ p2 ∂ μ/∂p, is negative and temperature independent. At T ∼ 17 K temperature dependence commences abruptly: κ-1 turns less negative with rising T and eventually reverses sign. An ideal classical gas is attained at temperatures comparable to the interaction energy, more than an order of magnitude larger than the Fermi energy. © 1996 The American Physical Society.