Excitonic dispersion of the intermediate-spin state in LaCoO$_3$ revealed by resonant inelastic X-ray scattering

TL;DR

This paper investigates excitonic dispersion in LaCoO$_3$ using resonant inelastic X-ray scattering to explore the potential realization of an excitonic insulator phase in a strongly correlated oxide.

Contribution

It provides experimental evidence for dispersive electron-hole excitations in LaCoO$_3$, supporting the theoretical proposal of excitonic insulator behavior in this material.

Findings

Observation of dispersive electron-hole excitations

Evidence supporting excitonic insulator phase in LaCoO$_3$

Experimental validation of theoretical predictions

Abstract

More than 50 years ago the electron-hole attraction was proposed to drive narrow gap semiconductors or semimetals to a new phase, the excitonic insulator. The experimental proof of its existence in bulk materials remains elusive. In strongly correlated insulators, the proximity of the excitonic insulator phase is reflected by the presence of dispersive electron-hole excitations with a small gap above a singlet ground state. Recently, such an excitation spectrum was proposed to be realized in perovskite oxide LaCoO$_3$. In this Letter we use Co $L_3$-edge resonant inelastic X-ray scattering to put this proposal to experimental test.