Inconsistencies between experimental and theoretical band structure of TiSe$_2$

TL;DR

This study compares experimental ARPES data with DFT calculations for TiSe$_2$, revealing significant discrepancies that challenge the excitonic insulator explanation for its charge density wave phase.

Contribution

The paper provides a direct comparison between experimental and theoretical band structures of TiSe$_2$, highlighting fundamental inconsistencies that question existing models.

Findings

Discrepancies between ARPES data and DFT calculations.

Absence of predicted hybridization gap in experimental data.

Challenges to the excitonic insulator scenario for TiSe$_2$.

Abstract

Renew interest in the charge density wave phase of TiSe$_2$ stems from the realization of its unique driving mechanism, the so called excitonic insulator phase. Existing claims are motivated by model calculations of the band structure. In this study, angle resolved photoemsision spectroscopy and density functional theory for TiSe$_2$ are directly compared. The substantial discrepancies found between the two descriptions cast serious doubts on the exitonic insulator scenario as the correct physical mechanism underlying the periodic lattice distortion at low temperature. In particular, the formation of a valence-conduction hybridization gap in the bulk band structure is not present in the experimental data. Therefore, the origin of the structural transition in TiSe$_2$ cannot be fully explained within the existing theoretical models.