Two temperature scales–(1) (single impurity) and/or (degenerate Fermi) and (2) crystal-electric-field splitting(s) Δ–provide the basis for dividing the excitation spectra of heavy-electron systems into three regimes. They are (i) for f atoms in a crystal field; (ii) for T∼, a bump appears in the specific heat due to the Kondo compensation; (iii) for T<, interaction effects between the f atoms lead to a Fermi-liquid solid where band-structure effects show up in the low-temperature properties (T</100). This paper is primarily concerned with region (i). In particular, we present new specific-heat data for up to 70 K and to 80 K. In comparing these data with those for other heavy-electron materials we conclude that the specific heat for T> is qualitatively consistent with the existence of crystal-electric-field levels, but that the overall experimental entropy is too high. We present a tentative model to account for this discrepancy through the use of Fermi statistics to describe transitions in a stylized band model with two peaks. Crystal-field levels in most cases have not been confirmed by neutron scattering.
DOI:https://doi.org/10.1103/PhysRevB.36.5330
©1987 American Physical Society