Thermally-induced Phases in an Ising Kondo Lattice Model on a Triangular Lattice: Partial Disorder and Kosterlitz-Thouless State

TL;DR

This study explores the thermal phase transitions in an Ising Kondo lattice model on a triangular lattice, revealing novel partially disordered and Kosterlitz-Thouless states driven by thermal fluctuations.

Contribution

It reports the first observation of a partially disordered phase in a two-dimensional localized spin model, stabilized by the Slater mechanism and accompanied by charge disproportionation.

Findings

Identification of four dominant phases including partially disordered and Kosterlitz-Thouless states.

Partially disordered phase is insulating and exhibits charge disproportionation.

Thermal fluctuations induce intermediate phases that are replaced at lower temperatures.

Abstract

Magnetic and electronic properties of a Kondo lattice model with Ising localized spins are studied on an isotropic triangular lattice. By using Monte Carlo simulation, we present that the model shows a rich phase diagram with four dominant states: two-sublattice stripe, three-sublattice ferrimganetic, partially disordered, and Kosterlitz-Thouless like quasi-long-range ordered states. Among them, the partially disordered state and Kosterlitz-Thouless like state are intermediate phases induced by thermal fluctuations in the phase competing regime; they are present only at finite temperatures and eventually taken over by another phases as the temperature is further lowered. Although the Kosterlitz-Thouless like state was found also in triangular Ising antiferromagnets with further-neighbor interactions, the partially disordered state has not been reported in the localized spin only models in two dimensions. Interestingly, the partially disordered phase is also peculiar in the charge degree of freedom of itinerant electrons; it is insulating and accompanied by charge disproportionation. From a combined analysis of a mean-field calculation of the band structure and Monte Carlo simulation, we conclude that the partial disorder in the present model is stabilized by the Slater mechanism.