How Electrons Become Mobile in a Colossal Dielectric -- Fe$_2$TiO$_5$

TL;DR

This study investigates the colossal permittivity in Fe$_2$TiO$_5$ single crystals, revealing that the same atomic forces influence both dipole relaxation and charge transport, indicating a bulk phenomenon near metallicity.

Contribution

It provides a detailed spectroscopic analysis linking dielectric relaxation and charge transport activation energies in Fe$_2$TiO$_5$, suggesting a microscopic origin of colossal dielectric behavior.

Findings

Relaxation response fits a Debye-like model with an energy barrier of ~286 meV.

DC transport shows an activation energy of ~289 meV.

Colossal dielectric behavior arises from atomic-scale forces near metallicity.

Abstract

We measure the colossal permittivity in single crystal Fe$_2$TiO$_5$ using broadband spectroscopy in the frequency range 20 Hz - 1 MHz. The relaxation response is analyzed using a Debye-like model with Arrhenius activation in two different ways and yields an energy barrier of 286.1 $\pm$ 2.8 meV. DC transport yields an activation energy of 288.8 $\pm$ 2.8 meV. These results strongly imply that the energy barrier for localized dipole motion and itinerant charge transport originate from the same atom-level forces. A further implication is that colossal dielectric behavior is a microscopic bulk phenomenon arising from a system on brink of metallicity.