Optical spectral weights and the ferromagnetic transition temperature of CMR manganites: relevance of double-exchange to real materials

TL;DR

This paper compares double-exchange models to experimental data on manganites, revealing that physics beyond double-exchange influences properties even in well-studied materials, and clarifies the role of kinetic energy in magnetic transition temperatures.

Contribution

It demonstrates the importance of factors beyond double-exchange in manganites and introduces the conduction band kinetic energy as a key parameter for understanding experimental data.

Findings

Physics beyond double-exchange is significant in La0.7Sr0.3MnO3.

Kinetic energy K is crucial for comparing models and data.

Reinterpretation of optical conductivity features and correction of phase diagram errors.

Abstract

We present a thorough and quantitative comparison of double-exchange models to experimental data on the colossal magnetoresistance manganese perovskites. Our results settle a controversy by showing that physics beyond double-exchange is important even in La$_{0.7}$Sr$_{0.3}$MnO$_3$, which has been regarded as a conventional double-exchange system. We show that the crucial quantity for comparisons of different calculations to each other and to data is the conduction band kinetic energy $K$, which is insensitive to the details of the band structure and can be experimentally determined from optical conductivity measurements. The seemingly complicated dependence of $T_c$ on the Hund's coupling $J$ and carrier concentration $n$ is shown to reflect the variation of $K$ with $J$, $n$ and temperature. We present results for the optical conductivity which allow interpretation of experiments and show that a feature previously interpreted in terms of the Hund's coupling was misidentified. We also correct minor errors in the phase diagram presented in previous work.