Paramagnetic scattering from heavy and moderately heavy fermions

Abstract

Heavy Fermions form an exotic branch of magnetism and have been studied extensively during the last two decades. The term heavy Fermions refers to highly correlated electron systems and is usually applied to rare earth and actinide metals, their alloys and intermetallic compounds which exhibit, among other interesting phenomena, two main characteristic properties: 1) enhanced Pauli paramagnetic susceptibility, i.e. constant c(o) as T → 0 K, and 2) enhanced linearly temperature dependent low temperature specific heat. These properties represent Fermi-liquid behavior, and in a free electron model for a metal, they are related to the conduction electron density of states at the Fermi level. The strongly enhanced coefficient yof the linear term in the specific heat interpreted this way suggests “quasiparticles” with very heavy “effective” mass at the Fermi level (up to – 2–3 orders of magnitude larger than the free electron mass). Observations of superconductivity in for example CeCu,Si, accompanied by a specific heat “jump” (the h-anomaly) consistent with heavy mass superconducting “carriers” [1] as well as the clear evidence for heavy “quasi-particles” on the Fermi surface from de Haas van Alphen measurements on CeSn, [2] represent two of the many remarkable manifestations of the heavy Fermion state.