Does (TaSe4)2I really harbor an axionic charge density wave?

TL;DR

This paper investigates the claim that (TaSe4)2I hosts an axionic charge density wave by examining its magnetoconductivity, finding no supporting evidence and questioning previous assumptions about its topological nature.

Contribution

The study provides experimental measurements challenging the hypothesis that (TaSe4)2I is an axionic insulator with a Weyl semimetal phase, emphasizing the importance of electron-phonon interactions.

Findings

No increase in magnetoconductivity observed

Highlights the specific Peierls transition in (TaSe4)2I

Questions the topological interpretation of the CDW in this compound

Abstract

A recent experimental work has reported an excess of the non-linear conductivity in the charge density wave (CDW) sliding mode of the quasi one-dimensional compound (TaSe4)2I, when a magnetic field is applied co-linearly to the electric field [Gooth et al., Nature 575, 315 (2019)]. This result has opened a conceptual approach, where the CDW gap in (TaSe4)2I is opened between Weyl fermions of opposite chirality with the assumption that this compound is a Weyl semi-metal in its undistorted high temperature phase. We report measurements in the sliding state of (TaSe4)2I performed in similar conditions. We have found no increase in the magnetoconductivity. In our attempts for understanding this unsettling discrepancy, we stress the specific nature of the Peierls transition in (TaSe4)2I and the strong electron-phonon coupling present in this compound. Given the lack of further evidence, we think that it is premature to assert that (TaSe4)2I is an axionic insulator.