Balancing orbital effects and onsite Coulomb repulsion through Na modulations in NaxVO2

TL;DR

This study reveals how Na modulations influence the electronic and structural properties of NaxVO2, highlighting a delicate balance between orbital effects and Coulomb repulsion, with implications for designing correlated materials.

Contribution

It introduces a sodium-modulated Peierls-like transition mechanism and demonstrates the sensitivity of NaxVO2's trimer structure to Coulomb interactions, advancing understanding of correlated vanadium oxides.

Findings

Na density waves follow a unified evolution pattern.

A Peierls-like transition mechanism is proposed.

The trimer structure's sensitivity to Coulomb repulsion is demonstrated.

Abstract

Vanadium oxides have been highly attractive for over half a century since the discovery of the metal insulator transition near room temperatures. Here NaxVO2 is studied through a systematic comparison with other layered sodium metal oxides with early 3d transition metals, first disclosing a unified evolution pattern of Na density waves through in situ XRD analysis. Combining ab-initio simulations and theoretical modelings, a sodium-modulated Peierls-like transition mechanism is then proposed for the bonding formation of metal ion dimers. More importantly, the unique trimer structure in NaxVO2 is shown to be very sensitive to the onsite Coulomb repulsion value, suggesting a delicate balance between strong electronic correlations and orbital effects that can be precisely modulated by both Na compositions and atomic stackings. This unveils a unique opportunity to design strongly correlated materials with tailored electronic transitions through electrochemical modulations and crystallographic designs, to elegantly balance various competition effects. We think the understanding will also help further elucidate complicated electronic behaviors in other vanadium oxide systems.