Electron and orbital correlations in Ca_{2-x}Sr_{x}RuO_{4} probed by optical spectroscopy

TL;DR

This study investigates how electron and orbital correlations in Ca_{2-x}Sr_{x}RuO_{4} evolve with doping and temperature using optical spectroscopy, revealing complex orbital ordering phenomena and electron-phonon interactions.

Contribution

It provides a systematic analysis of optical spectra across doping levels, highlighting the coexistence of different orbital ordering states and the role of electron-phonon interactions.

Findings

Observation of two correlation-induced peaks at 1.0 and 1.9 eV in the Mott insulating state

Shift of low-frequency peak with temperature indicating electron-phonon interactions

Evidence for coexistence of antiferro- and ferro-orbital ordering states

Abstract

The doping and temperature dependent optical conductivity spectra of the quasi-two-dimensional Ca_{2-x}Sr_xRuO_4 (0.0=<x=<2.0) system were investigated. In the Mott insulating state, two electron correlation-induced peaks were observed around 1.0 and 1.9 eV, which could be understood in terms of the 3-orbital Hubbard model. The low frequency peak showed a shift toward higher frequency as temperature was lowered, which indicated that electron-phonon interactions play an important role in the orbital arrangements. From the systematic analysis, it was suggested that the antiferro-orbital and the ferro-orbital ordering states could coexist.