Dynamic conductivity of semiconducting manganites approaching the metal-insulator transition

TL;DR

This study investigates how the electrical conductivity of La1-xSrxMnO3 manganites changes across the metal-insulator transition, revealing the evolution from hopping transport to metallic behavior with increasing Sr doping.

Contribution

It provides comprehensive frequency-dependent conductivity data across the transition, combining dielectric and infrared spectra to elucidate charge transport mechanisms.

Findings

Hopping transport dominates at low doping levels.

Polaronic excitations develop with increased doping.

Drude response appears in the metallic state.

Abstract

We report the frequency-dependent conductivity of the manganite system La1-xSrxMnO3 (x <= 0.2) when approaching the metal-insulator transition from the insulating side. Results from low-frequency dielectric measurements are combined with spectra in the infrared region. For low doping levels the behavior is dominated by hopping transport of localized charge carriers at low frequencies and by phononic and electronic excitations in the infrared region. For the higher Sr contents the approach of the metallic state is accompanied by the successive suppression of the hopping contribution at low frequencies and by the development of polaronic excitations in the infrared region, which finally become superimposed by a strong Drude contribution in the fully metallic state.