Phenemenological and Some Microscopic Aspects of Heavy Fermi-Liquids and Their Superconductivity

Abstract

There appears to be three regimes [1] in the physics of the rare-earth and actinide metals and compounds. The local moment regime which is the most frequent occurs when the ionization level of the f-orbitals is well below the chemical potential. The other two regimes may well be called the confined moment regime since magnetic moments which are free at high temperatures (Curie-Weiss susceptibility) so not show themselves in any property at low temperatures (and low frequencies). Instead a Fermi-liquid behavior (Pauli susceptibility and linear specific heat) obtains. If the f-ionization potential pins the chemical potential we have the valence fluctuation regime, while if it is below, but not too far below, the so-called heavy Fermion behavior obtains. Some of the valence fluctuation materials are semiconductors, but when they are not, there is little qualitative distinction in their low temperature properties from the heavy Fermi-liquids. The effective mass is of 0(10–10²) in the former and 0(10²–10³) in the latter. Although phenemenologically the valence fluctuators are similar to the heavy Fermions, microscopically they are different. The average f-occupation is far from integral, so that real quantum-mechanical f-charge fluctuations are essential, while in the latter case such fluctuations may be ignored. A. Zawadowski and I have recently completed calculations of a two component interacting electron gas model suitable for valence fluctuators. One of our conclusions is that the singularities of the problem are primarily driven by inter-component spin interactions and that inter-component charge (valence) fluctuations do not determine the low temperature state.