Dielectric properties and dynamical conductivity of LaTiO3: From dc to optical frequencies

TL;DR

This paper provides a comprehensive analysis of LaTiO3's dielectric and conductivity properties across a broad frequency and temperature range, revealing insights into its charge transport, structural transitions, and Mott-Hubbard insulating behavior.

Contribution

It offers the first detailed broadband frequency characterization of LaTiO3's dielectric and ac conductivity, linking structural, electronic, and magnetic properties.

Findings

Evidence of Anderson localization affecting charge transport.

Detection of a structural phase transition at magnetic ordering temperature.

Observation of a gap-like electronic excitation consistent with Mott-Hubbard insulators.

Abstract

We provide a complete and detailed characterization of the temperature-dependent response to ac electrical fields of LaTiO3, a Mott-Hubbard insulator close to the metal-insulator transition. We present combined dc, broadband dielectric, mm-wave, and infrared spectra of ac conductivity and dielectric constant, covering an overall frequency range of 17 decades. The dc and dielectric measurements reveal information on the semiconducting charge-transport properties of LaTiO3, indicating the importance of Anderson localization, and on the dielectric response due to ionic polarization. In the infrared region, the temperature dependence of the phonon modes gives strong hints for a structural phase transition at the magnetic ordering temperature. In addition, a gap-like electronic excitation following the phonon region is analyzed in detail. We compare the results to the soft-edge behavior of the optical spectra characteristic for Mott-Hubbard insulators. Overall a consistent picture of the charge-transport mechanisms in LaTiO3 emerges.