Visualizing topological defects of charge density wave in Weyl semimetal (TaSe₄)₂I

The charge-density-wave (CDW) compound (TaSe₄)₂I is recently established as a Weyl semimetal above its CDW transition temperature (~260 K) [1]. It has been proposed that CDW nesting of Weyl nodes could lead to the correlated axionic insulator state of matter [2,3]. A recent transport study suggests that (TaSe₄)₂I is a candidate of axionic CDW [4]. However, it is still under debate whether (TaSe₄)₂I in the CDW phase is an axion insulator [5]. In theory, axionic CDW carries one-dimensional gapless modes called axion strings at the CDW dislocations [2,3]. The in-gap states could be detected by tunneling spectroscopy, providing smoking-gun evidence of the axionic CDW phase. Here we present the first comprehensive real-space characterization of CDW modulation and CDW edge dislocations in (TaSe₄)₂I using scanning tunneling microscopy and spectroscopy (STM/STS). Our tunneling spectroscopic results on the CDW edge dislocations shed light on the topological nature of the CDW phase.

 

References

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