Orbital dynamics: The origin of the anomalous optical spectra in ferromagnetic manganites

TL;DR

This paper investigates how orbital degeneracy influences the optical and thermodynamic properties of ferromagnetic manganites, revealing that orbital fluctuations cause the observed anomalous spectra and strong correlations.

Contribution

It introduces an orbital t-J model treated with a slave-boson approach to explain the optical conductivity and specific heat in ferromagnetic manganites, highlighting the role of orbital fluctuations.

Findings

Optical conductivity shows a broad incoherent component and suppressed Drude weight.

Calculated T-linear specific heat matches experimental data.

Orbital fluctuations are identified as key to the correlated metallic phase.

Abstract

We discuss the role of orbital degeneracy in the transport properties of perovskite manganites, focusing in particular on the optical conductivity in the metallic ferromagnetic phase at low temperatures. Orbital degeneracy and strong correlations are described by an orbital t-J model which we treat in a slave-boson approach. Employing the memory-function formalism we calculate the optical conductivity, which is found to exhibit a broad incoherent component extending up to bare bandwidth accompanied by a strong suppression of the Drude weight. Further, we calculate the constant of T-linear specific heat. Our results are in overall agreement with experiment and suggest low-energy orbital fluctuations as the origin of the strongly correlated nature of the metallic phase of manganites.