Electronic phase transitions in the spin-1/2 Falicov-Kimball model.

Abstract

The spin-1/2 Falicov-Kimball model for electronically driven valence and metal-insulator transitions is studied in one dimension using small-cluster exact diagonalization calculations. The resultant exact solutions are used to examine the f-state occupation (${\mathit{n}}_{\mathit{f}}$) as a function of f-level energy (${\mathit{E}}_{\mathit{f}}$), d-f interaction strength G, and f-f interaction strength U. It is shown that for sufficiently large values of G (G>2) the model can describe two types of discontinuous valence transitions: the insulator-metal transitions from an integer-valence ground state (${\mathit{n}}_{\mathit{f}}$=1) into an inhomogeneous intermediate-valence ground state (0${\mathit{n}}_{\mathit{f}}$1) and the insulator-metal transitions from ${\mathit{n}}_{\mathit{f}}$=1 to ${\mathit{n}}_{\mathit{f}}$=0. In the weak-coupling limit (G1) the model undergoes a few consecutive discontinuous and continuous intermediate-valence transitions. In addition, the local pairing of f electrons and some other features of the spin-1/2 Falicov-Kimball model are discussed. \textcopyright{} 1996 The American Physical Society.