Theory of optical conductivity in doped manganites

TL;DR

This paper explains the optical conductivity behavior in doped manganites using bipolaron theory, linking spectral weight transfer and colossal magnetoresistance to bipolaron dissociation during the ferromagnetic transition.

Contribution

It introduces a bipolaron-based theoretical framework to explain the optical and magnetic properties of doped manganites.

Findings

Spectral weight shifts to lower frequencies below Curie temperature.

Colossal magnetoresistance correlates with bipolaron dissociation.

Optical conductivity changes are explained by exchange interactions.

Abstract

The frequency and temperature dependence of the optical conductivity of ferromagnetic manganites is explained within the framework of the bipolaron theory. As these materials are cooled below the Curie temperature, the colossal magnetoressitance (CMR) is accompanied by a massive transfer of the spectral weight of the optical conductivity to lower frequencies. As with the CMR itself, this change in the optical conductivity is explained by the dissociation of bipolarons into small polarons by exchange interaction with the localized Mn spins during the transition to the low temperature ferromagnetic phase.