Some exact results for dilute mixed-valent and heavy-fermion systems

Abstract

Numerous exact results for magnetic impurities in simple metals have been obtained during the last eight years. These systems exhibit a variety of unusual low-temperature properties attributed to highly correlated electronic states, e.g. a mixed valence and large electronic contributions to the specific heat and the magnetic susceptibility. Some of these exact results obtained by means of the generalized Bethe Ansatz are reviewed here. Special emphasis is given to the solution of the degenerate Anderson model, in particular in the presence of mechanisms lifting the degeneracy of the f-level, e.g. crystalline fields, spin-orbit coupling and the magnetic field. This focus makes the present article complementary to the previous ones by Andrei, Furuya and Lowenstein and by Tsvelick and Wiegmann. Comparisons between theory and experiments are also reviewed.