Role of surface termination in the metal-insulator transition of V$_2$O$_3$(0001) ultrathin films

TL;DR

This study investigates how different surface terminations in ultrathin V₂O₃ films influence the metal-insulator transition, revealing surface effects, spectral weight redistribution, and the importance of electron correlations.

Contribution

It demonstrates that surface termination can suppress or modify the MIT in V₂O₃ films and highlights the role of surface effects and electron correlations in the transition.

Findings

MIT can be partially or fully suppressed at the surface

Spectral weight redistributes across the MIT

Spectral weight sum rules break down in the system

Abstract

Surface termination is known to play an important role in determining the physical properties of materials. It is crucial to know how surface termination affects the metal-insulator transition (MIT) of V$_2$O$_3$ films for both fundamental understanding and its applications. By changing growth parameters, we achieved a variety of surface terminations in V$_2$O$_3$ films that are characterized by low energy electron diffraction (LEED) and photoemission spectroscopy techniques. Depending upon the terminations, our results show MIT can be partially or fully suppressed near the surface region due to the different filling of the electrons at the surface and sub-surface layers and change of screening length compared to the bulk. Across MIT, a strong redistribution of spectral weight and its transfer from high-to-low binding energy regime is observed in a wide-energy-scale. Our results show total spectral weight in the low-energy regime is not conserved across MIT, indicating a breakdown of `sum rules of spectral weight', a signature of a strongly correlated system. Such change in spectral weight is possibly linked to the change in hybridization, lattice volume ({\it i.e.,} effective carrier density), and spin degree of freedom in the system that happens across MIT. We find that MIT in this system is strongly correlation-driven where the electron-electron interactions play a pivotal role. Moreover, our results provide a better insight in understanding the electronic structure of strongly correlated systems and highlight the importance of accounting surface effects during interpretation of the physical property data mainly using surface sensitive probes, such as surface resistivity.