Observation of metallic electronic structure in a single-atomic-layer oxide

TL;DR

This study demonstrates that a monolayer of SrRuO3 exhibits a strongly correlated metallic phase with tunable electronic properties, challenging the typical insulating behavior of single-atomic-layer transition metal oxides.

Contribution

It provides the first evidence of a metallic phase in monolayer SrRuO3 and explores the interplay of dimensionality and electronic correlation in two-dimensional oxides.

Findings

Monolayer SrRuO3 is a strongly correlated metal.

Charge modulation induces an incoherent-to-coherent crossover.

The electronic phase is highly tunable via charge modulation.

Abstract

Correlated electrons in transition metal oxides (TMOs) exhibit a variety of emergent phases. When TMOs are confined to a single-atomic-layer thickness, experiments so far have shown that they usually lose diverse properties and become insulators. In an attempt to extend the range of electronic phases of the single-atomic-layer oxide, we search for a metallic phase in a monolayer-thick epitaxial SrRuO$_3$ film. Combining atomic-scale epitaxy and angle-resolved photoemission measurements, we show that the monolayer SrRuO$_3$ is a strongly correlated metal. Systematic investigation reveals that the interplay between dimensionality and electronic correlation makes the monolayer SrRuO$_3$ an incoherent metal with orbital-selective correlation. Furthermore, the unique electronic phase of the monolayer SrRuO$_3$ is found to be highly tunable, as charge modulation demonstrates an incoherent-to-coherent crossover of the two-dimensional metal. Our work emphasizes the potentially rich phases of single-atomic-layer oxides and provides a guide to the manipulation of their two-dimensional correlated electron systems.