Pressure Dependence of the Specific Heat of Heavy-Fermion Compounds

Measurement of the properties of materials as a function of pressure (P) provides an additional dimension for comparison with models and theoretical calculations. It also provides a relatively sound basis for establishing correlations between different properties. For example, if one looks for correlations between superconductivity and magnetic properties by studying series of different compounds or alloys, one is forced to resort to comparisons that are complicated, to a very substantial degree, by chemical and structural differences. If instead one studies the pressure dependence of the properties of a single material, only one relatively simple parameter, the volume (V), is changed. Measurement of the pressure dependence of the properties of heavy-fermion compounds (HFC) is particularly fruitful because the 4f and 5f electrons, which play the central role in the phenomenon, are extremely sensitive to pressure, and large effects are observed at modest pressures. Although the electrical resistivity (ρ) and the magnetic susceptibility (χ) of a number of HFC have been measured as a function of pressure, it is only recently that data for the specific heat (C) have become available for non-zero pressure. We describe here measurements of C(P) to P ∼ 9 kbar for CeA13 [1], CeCu6 [2], UBe13 [3], and UPt3 [4]. Independent measurements of C(P) to P ∼ 6 kbar have been reported for CeCu2Si2 [5].