# Evidence for an axionic charge density wave in the Weyl semimetal (TaSe4)2I

## TL;DR

This study provides experimental evidence for an axionic charge density wave in the Weyl semimetal (TaSe4)2I, revealing axion-related magneto-electric effects linked to the chiral anomaly and phason dynamics.

## Contribution

First experimental detection of an axionic charge density wave in a Weyl semimetal, demonstrating axion-related magneto-conductance effects under parallel electric and magnetic fields.

## Key findings

- Large positive magneto-conductance in (TaSe4)2I under E||B
- Angular dependence consistent with axionic transport
- Observation of chiral anomaly contribution to phason current

## Abstract

An axion insulator is a correlated topological phase, predicted to arise from the formation of a charge density wave in a Weyl semimetal. The accompanying sliding mode in the charge density wave phase, the phason, is an axion. It is expected to cause anomalous magneto-electric transport effects. However, this axionic charge density wave has so far eluded experimental detection. In this paper, we report the observation of a large, positive contribution to the magneto-conductance in the sliding mode of the charge density wave Weyl semimetal (TaSe4)2I for collinear electric and magnetic fields (E||B). The positive contribution to the magneto-conductance originates from the anomalous axionic contribution of the chiral anomaly to the phason current, and is locked to the parallel alignment of E and B. By rotating B, we show that the angular dependence of the magneto-conductance is consistent with the anomalous transport of an axionic charge density wave.

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Source: https://tomesphere.com/paper/1906.04510