Fermi Liquid - Non-Fermi Liquid Transition in the Double Exchange Model

Abstract

Motivated by recent discovery of colossal magnetoresistance in La${}_{(}1-x)$Ca$x$MnO${}_3$ and other manganites, we have studied the double exchange model. We argue that the forced alignment of conduction-electron spin with the core spins that causes ferromagnetism also projects out a large part of the Hilbert space needed for coherent propagation of electrons carrying spin and charge. As a result, the electron becomes a composite object and its Green's function exhibits a two-fluid character: a coherent Fermi-liquid component associated with the ferromagnetically ordered core spins, and a non-Fermi liquid component associated with the disordered spins. With increasing temperature, there is continuous transfer of spectral weight from the Fermi liquid to the non-Fermi liquid component, until the former disappears above $T_c$. In an applied field spectral weight is transferred from the non-Fermi liquid to the component. Implications for the manganites are discussed.

Latex file. 11 pages. 2 figures available on request. ([email protected]) (after Aug. 3, [email protected])