Band Structure and Terahertz Optical Conductivity of Transition Metal Oxides: Theory and Application to CaRuO$_3$

TL;DR

This study uses advanced calculations to show how structural distortions in transition metal oxides like CaRuO$_3$ influence terahertz optical conductivity, explaining experimental observations without invoking non-Fermi-liquid physics.

Contribution

It demonstrates that low-energy optical features in CaRuO$_3$ can be explained by band structure effects combined with Fermi-liquid self-energy, challenging previous interpretations of non-Fermi-liquid behavior.

Findings

Structural distortions cause low-energy optical transitions.

Band structure effects mimic non-Fermi-liquid signatures.

Fermi-liquid model explains terahertz response in CaRuO$_3$.

Abstract

Density functional plus dynamical mean field calculations are used to show that in transition metal oxides, rotational and tilting (GdFeO$_3$-type) distortions of the ideal cubic perovskite structure produce a multiplicity of low-energy optical transitions which affect the conductivity down to frequencies of the order of $1$ or $2$~mV (terahertz regime), mimicking non-Fermi-liquid effects even in systems with a strictly Fermi-liquid self-energy. For CaRuO$_3$, a material whose measured electromagnetic response in the terahertz frequency regime has been interpreted as evidence for non-Fermi-liquid physics, the combination of these band structure effects and a renormalized Fermi-liquid self-energy accounts for the low frequency optical response which had previously been regarded as a signature of exotic physics. Signatures of deviations from Fermi-liquid behavior at higher frequencies ($\sim 100$~meV) are discussed.