Double Exchange Models: Self Consistent Renormalisation

TL;DR

This paper introduces a self-consistent scheme to derive classical spin Hamiltonians from Hund's coupled spin-fermion models in the strong coupling limit, enabling analysis of larger systems and properties like transport without artificial broadening.

Contribution

It develops a formalism for self-consistently renormalizing exchange couplings in double exchange models, extending analysis capabilities beyond exact simulation limits.

Findings

Method allows larger system size analysis.

Enables study of transport and optical properties.

Results agree with exact simulations on small systems.

Abstract

We propose a scheme for constructing classical spin Hamiltonians from Hunds coupled spin-fermion models in the limit J_H/t \to \infinity. The strong coupling between fermions and the core spins requires self-consistent calculation of the effective exchange in the model, either in the presence of inhomogeneities or with changing temperature. In this paper we establish the formalism and discuss results mainly on the ``clean'' double exchange model, with self consistently renormalised couplings, and compare our results with exact simulations. Our method allows access to system sizes much beyond the reach of exact simulations, and we can study transport and optical properties of the model without artificial broadening. The method discussed here forms the foundation of our papers Phys. Rev. Lett. 91, 246602 (2003), and Phys. Rev. Lett. 92, 126602 (2004).