Orbital-selective Mass Enhancements in Multi-band Ca$_{2-x}$Sr$_{x}$RuO$_{4}$ Systems Analyzed by the Extended Drude Model

TL;DR

This study uses the extended Drude model to analyze optical spectra of Ca$_{2-x}$Sr$_{x}$RuO$_{4}$, revealing orbital-specific mass enhancements primarily due to the $d_{xy}$ band renormalization, not Mott-gap opening.

Contribution

It demonstrates that the heavy mass state near $x=0.5$ arises from $d_{xy}$ band effects, challenging the orbital-selective Mott-gap hypothesis.

Findings

Mass enhancement peaks near $x=0.5$

Mott-gap opening not responsible for mass increase

Heavy mass linked to $d_{xy}$ band renormalization

Abstract

We investigated optical spectra of quasi-two-dimensional multi-band Ca$% _{2-x} $Sr$_{x}$RuO$_{4}$ systems. The extended Drude model analysis on the ab-plane optical conductivity spectra indicates that the effective mass should be enhanced near $x=0.5$. Based on the sum rule argument, we showed that the orbital-selective Mott-gap opening for the $d_{yz/zx}$ bands, the widely investigated picture, could not be the origin of the mass enhancement. We exploited the multi-band effects in the extended Drude model analysis, and demonstrated that the intriguing heavy mass state near $x=0.5$ should come from the renormalization of the $d_{xy}$ band.