Manifestation of Correlation Effects in the photoemission spectra of Ca$_{1-x}$Sr$_x$RuO$_3$

TL;DR

This study investigates how structural distortion affects electron correlation in Ca$_{1-x}$Sr$_x$RuO$_3$ thin films, revealing spectral weight transfer and band narrowing near the Fermi level through photoemission and absorption spectra.

Contribution

It demonstrates that orthorhombic distortion enhances electron correlation effects without changing the Ru 4d bandwidth, providing insight into correlation phenomena in this material.

Findings

Spectral weight shifts from coherent to incoherent parts with increasing distortion.

Band narrowing occurs near the Fermi level despite unchanged bandwidth.

Strong mass enhancement observed in specific heat data.

Abstract

We have measured soft x-ray photoemission and O 1{\it s} x-ray absorption spectra of Ca$_{1-x}$Sr$_x$RuO$_3$ thin films prepared {\it in situ}. The coherent and incoherent parts have been identified in the bulk component of the photoemission spectra, and spectral weight transfer from the coherent to the incoherent part has been observed with decreasing $x$, namely, with increasing orthorhombic distortion. We propose that, while the Ru 4d one-electron bandwidth does not change with $x$, the distortion and hence the splitting of the $t_{2\text{g}}$ band effectively increases electron correlation strength. Although strong mass enhancement is found in the electronic specific heat data, the coherent part remains wide, suggesting enhanced band narrowing only in the vicinity of {\it E$_{F}$}.