Resonant soft x-ray emission as a bulk probe of correlated electron behavior in metallic Sr$_x$Ca$_{1-x}$VO$_3$

TL;DR

This study uses resonant soft x-ray emission spectroscopy alongside other methods to investigate how electron correlation varies between surface and bulk in Sr$_x$Ca$_{1-x}$VO$_3$, revealing enhanced correlation effects at the surface.

Contribution

It demonstrates that resonant soft x-ray emission is an effective bulk probe for correlated electron behavior, highlighting differences between surface and bulk electronic structures.

Findings

Incoherent Hubbard bands are closer to quasiparticle features at the surface.

Bandwidth narrows by about 10% at the surface.

Electron correlation effects are stronger at the surface.

Abstract

The evolution of electron correlation in Sr$_{x}$Ca$_{1-x}$VO$_3$ has been studied using a combination of bulk-sensitive resonant soft x-ray emission spectroscopy (RXES), surface-sensitive photoemission spectroscopy (PES), and ab initio band structure calculations. We show that the effect of electron correlation is enhanced at the surface. Strong incoherent Hubbard subbands are found to lie ~ 20% closer in energy to the coherent quasiparticle features in surface-sensitive PES measurements compared with those from bulk-sensitive RXES, and a ~ 10% narrowing of the overall bandwidth at the surface is also observed.