Absence of in-gap modes in charge density wave edge dislocations of the Weyl semimetal (TaSe$_4$)$_2$I

TL;DR

This study uses scanning tunneling microscopy and spectroscopy to investigate charge density waves in (TaSe4)2I, finding no evidence of in-gap modes at edge dislocations and suggesting a non-Peierls mechanism for the CDW.

Contribution

The paper provides the first detailed real-space analysis of CDW edge dislocations in (TaSe4)2I, revealing the absence of in-gap modes and clarifying the nature of the CDW mechanism.

Findings

No in-gap states observed at CDW edge dislocations.

CDW dominated by lattice distortion rather than charge modulation.

CDW gap measured at approximately 200 meV.

Abstract

Axion electrodynamics in condensed matter could emerge from the formation of charge density waves (CDWs) in Weyl semimetals. (TaSe$_4$)$_2$I was proposed to be the first material platform for realizing axionic CDW that may host topological defects with one-dimensional in-gap modes. The real-space modulation of the CDW phase and the existence of in-gap modes remain elusive. Here, we present a comprehensive scanning tunneling microscopic and spectroscopic study of a CDW on a (TaSe$_4$)$_2$I (110) surface. The tunneling spectroscopic measurements reveal a CDW gap of $\sim 200$ meV, in good agreement with prior studies, while the spectroscopy of CDW edge dislocation shows no indication of in-gap states. The bias-dependent scanning tunneling microscopy images indicate that the CDW in(TaSe$_4$)$_2$I is dominated by a large periodic lattice distortion instead of charge modulation, suggesting a non-Peierls mechanism of the CDW instability.