Ordering of localized moments in Kondo lattice models

TL;DR

This paper investigates the quantum phase transition in one-dimensional Kondo lattice models, revealing how localized spins transition from ferromagnetic to paramagnetic phases influenced by conduction band filling and electron coupling.

Contribution

It establishes a connection between the ferromagnetic-paramagnetic transition and the quantum Ising chain, providing a critical line equation and analyzing the effects of various couplings.

Findings

Transition described as quantum order-disorder transition

Diverging susceptibility in the paramagnetic phase

Range of double-exchange interaction determined

Abstract

We describe the transition from a ferromagnetic phase, to a disordered para- magnetic phase, which occurs in one-dimensional Kondo lattice models with partial conduction band filling. The transition is the quantum order-disorder transition of the transverse-field Ising chain, and reflects double-exchange ordered regions of localized spins being gradually destroyed as the coupling to the conduction electrons is reduced. For incommensurate conduction band filling, the low-energy properties of the localized spins near the transition are dominated by anomalous ordered (disordered) regions of localized spins which survive into the paramagnetic (ferromagnetic) phase. Many interesting properties follow, including a diverging susceptibility for a finite range of couplings into the paramagnetic phase. Our critical line equation, together with numerically determined transition points, are used to determine the range of the double-exchange interaction. Models we consider are the spin 1/2 Kondo lattices with antiferromagnetic (Kondo) coupling, with ferromagnetic (Hund's rule) coupling, and the Kondo lattice with repulsive interactions between the conduction electrons.