Correlated Mean Field Ansatz for the Kondo Necklace

TL;DR

This paper introduces a correlated mean field variational approach to study the ground state phase diagram of the Kondo lattice model, revealing suppressed magnetic transitions and strongly reduced moments at strong coupling.

Contribution

It develops a novel variational trial state incorporating intersite correlations, improving understanding of the Kondo lattice ground state beyond standard mean field methods.

Findings

Correlated trial states favor antiparallel triplet alignment at large Kondo couplings.

Magnetic-to-Kondo transition is suppressed with the correlated approach.

Strong coupling ground state exhibits magnetic order with reduced moments.

Abstract

We study the ground state phase diagram of the pseudospin model introduced by Doniach to describe the essential physics of Kondo lattices. We use variational trial states which augment the usual mean field solution by incorporating various intersite correlations. A composite spin correlation describing the antiparallel alignment of fluctuating triplets is found to be particularly favourable for large Kondo couplings. With this trial state, the magnetic--to--Kondo transition is suppressed and the strong coupling ground state is ordered with strongly reduced moments. The relevance of the findings is discussed.