Electronic band structure of Ti2O3 thin films studied by angle-resolved photoemission spectroscopy

TL;DR

This study investigates the electronic band structure of Ti2O3 thin films using ARPES, revealing the importance of electron-electron correlation and suggesting the MIT is driven by Fermi surface changes due to lattice deformation.

Contribution

First direct ARPES measurement of Ti2O3 thin films' band structure, clarifying the role of electron correlations and the MIT mechanism.

Findings

Band dispersion observed on Ti2O3 surface

Band structures agree with DFT+U calculations at U=2.2 eV

MIT driven by Fermi surface changes due to lattice deformation

Abstract

Ti2O3 exhibits a unique metal-insulator transition (MIT) at approximately 450 K over a wide temperature range of ~ 150 K. This broad MIT accompanied by lattice deformation differs from the sharp MITs observed in most other transition-metal oxides. A long-standing issue is determining the role of electron-electron correlation in the electronic structure and MIT of Ti2O3. However, the lack of information about the band structure of Ti2O3 has hindered investigating the origin of its unusual physical properties. Here, we report the electronic band structure of insulating Ti2O3 films with slight hole doping by angle-resolved photoemission spectroscopy (ARPES). ARPES showed clear band dispersion on the surface of single-crystalline epitaxial films. The experimentally obtained band structures were compared with band-structure calculation results based on density functional theory (DFT) with generalized gradient approximation + U correction. The obtained band structures are in good agreement with the DFT calculations at U = 2.2 eV, suggesting that electron-electron correlation plays an important role in the electronic structure of Ti2O3. Furthermore, the detailed analyses with varying U suggest that the origin of the characteristic MIT in Ti2O3 is a semimetal-semimetal or semimetal-semiconductor transition caused by changes in the Fermi surface due to lattice deformation.