Non-uniform phases in metals with local moments

TL;DR

This paper investigates the phase diagram of a 2D Kondo lattice model with complex exchange interactions, revealing that non-uniform, symmetry-breaking phases like flux and columnar states are more stable than uniform order.

Contribution

It introduces a mean-field analysis allowing for lattice symmetry breaking, identifying the stability of flux and columnar phases depending on interaction signs and electron filling.

Findings

Flux phase is always stable for ferromagnetic J_1.

For antiferromagnetic J_1, either flux or columnar phases occur.

Non-uniform phases dominate over uniform order in the studied model.

Abstract

The two-dimensional Kondo lattice model with both nearest and next-nearest neighbor exchange interactions is studied within a mean-field approach and its phase diagram is determined. In particular, we allow for lattice translation symmetry breaking. We observe that the usual uniform inter-site order parameter is never realized, being unstable towards other more complex types of order. When the nearest neighbor exchange J_1 is ferromagnetic the flux phase is always the most stable state, irrespective of the value of the next-nearest-neighbor interaction J_2. For antiferromagnetic J_1, however, either a columnar or a flux phase is realized, depending on conduction electron filling and the value of J_2.