Electronic Instability in a Zero-Gap Semiconductor: the Charge-Density Wave in (TaSe4)2I

TL;DR

This study combines ARPES and first-principles calculations to explore the electronic structure and charge-density wave phenomena in (TaSe4)2I, revealing a zero-gap semiconductor with interchain coupling and polaron formation driving a CDW transition.

Contribution

It provides a comprehensive analysis of (TaSe4)2I, demonstrating the role of interchain coupling and polarons in CDW formation, supported by both experimental and theoretical methods.

Findings

(TaSe4)2I is a zero-gap semiconductor with interchain coupling.

CDW formation occurs below 263 K with incommensurability due to interchain effects.

Polaron formation explains the semiconductor-to-semiconductor transition.

Abstract

We report a comprehensive study of the paradigmatic quasi-1D compound (TaSe4)2I performed by means of angle-resolved photoemission spectroscopy (ARPES) and first-principles electronic structure calculations. We find it to be a zero-gap semiconductor in the non-distorted structure, with non-negligible interchain coupling. Theory and experiment support a Peierls-like scenario for the CDW formation below T_CDW = 263 K, where the incommensurability is a direct consequence of the finite interchain coupling. The formation of small polarons, strongly suggested by the ARPES data, explains the puzzling semiconductor-to-semiconductor transition observed in transport at T_CDW.