INTEGRABLE MIXED-VALENCE IMPURITY IN A ONE-DIMENSIONAL CORRELATED ELECTRON LATTICE

We consider spin-1/2 electrons on a chain with nearest neighbor hoppin g t constrained by the excluded multiple occupancy of the lattice site s, and spin-exchange J and charge interaction between neighboring site s. The model is integrable at the supersymmetric point, J = 2t, where charges and spin form a SU(3) superalgebra. The model differs from the traditional t-J model, where the supersymmetry arises as a graded FFB permutation, rather than a BBB algebra. Without destroying the integr ability of the model we introduce an impurity of arbitrary spin S, whi ch hybridizes with the conduction states of the host. The discrete Bet he ansatz equations diagonalizing the correlated host with impurity ar e derived and the solutions are classified according to the string hyp othesis. The thermodynamic Bethe ansatz equations and the impurity fre e energy are obtained. The ground state properties of the host and the impurity are studied as a function of Che band-filling and the Kondo exchange coupling. The impurity has a magnetic ground state for S > 1/ 2 and in general mixed valent properties. (C) 1997 Published by Elsevi er Science B.V.