Electronic Phase Switching in the Negative Charge Transfer Energy SrCoO_x Thin Films with the Mottronic Relevancies

The metal–insulator transition in the negative charge transfer energy (Δ) materials is at the cutting edge for the transition-metal oxide community owing to their tremendous prospects in the Mottronic applications. We demonstrate the underlying mechanism for the Mott-switching in the thin films of negative Δ insulator SrCoO2.5 and negative Δ metal SrCoO3 systems. The control on the lowest energy charge fluctuation energetics in terms of the Coulomb repulsion U and Δ for the electronic phase switching is realized, and a comprehensive picture of the opening and closing of the band gap has been drawn experimentally in the negative Δ regime. The charge disproportionation is observed in the insulating regime, which is melted in the metallic regime of negative Δ in the SrCoOx films. From the electronic structure investigation, we have established the positions of the SrCoOx thin films in the U–Δ phase space and identified the tunable parameters for the electronic phase switching in the films. This study is fundamentally important for understanding the electronic correlation parameters controlling the lowest energy charge fluctuation energetics for the Mott-switching in the negative Δ regime, making SrCoOx thin films a promising candidate for the future Mottronic applications.