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

TL;DR

This paper investigates the transition from Fermi liquid to non-Fermi liquid behavior in the double exchange model, explaining how electron coherence is affected by spin alignment and temperature, with implications for manganite materials.

Contribution

It introduces a two-fluid model describing coherent and incoherent electron components in the double exchange system, highlighting the impact of spin order and temperature on electron spectral weight transfer.

Findings

Spectral weight shifts from Fermi liquid to non-Fermi liquid with increasing temperature.

Applied magnetic field transfers spectral weight back to the Fermi liquid component.

Electron Green's function exhibits a two-fluid character due to spin alignment effects.

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.