Electronic characteristics of ultrathin SrRuO$_3$ films and their relationship with the metal$-$insulator transition

TL;DR

This study investigates the electronic structure of ultrathin SrRuO$_3$ films using EEL spectroscopy and DFT, revealing how thickness influences the metal-insulator transition and the role of substrate interactions.

Contribution

It provides detailed spatially resolved electronic characterization of ultrathin SRO films and links their properties to the metal-insulator transition and substrate effects.

Findings

Distinct electronic features in the central layer of insulating SRO

EEL spectra near STO substrate resemble those of STO

DFT-based density of states partially match spectral features

Abstract

SrRuO$_3$ (SRO) films are known to exhibit insulating behavior as their thickness approaches four unit cells. We employ electron energy$-$loss (EEL) spectroscopy to probe the spatially resolved electronic structures of both insulating and conducting SRO to correlate them with the metal$-$insulator transition (MIT). Importantly, the central layer of the ultrathin insulating film exhibits distinct features from the metallic SRO. Moreover, EEL near edge spectra adjacent to the SrTiO$_3$ (STO) substrate or to the capping layer are remarkably similar to those of STO. The site$-$projected density of states based on density functional theory (DFT) partially reflects the characteristics of the spectra of these layers. These results may provide important information on the possible influence of STO on the electronic states of ultrathin SRO.