A Charge-Density-Wave Topological Semimetal

TL;DR

This study reveals that (TaSe$_4$)$_2$I is a Weyl semimetal at room temperature with a CDW-induced topological phase transition, combining strong correlations and topological properties, and opening pathways for novel quantum phenomena.

Contribution

It demonstrates a correlation-driven topological phase transition in (TaSe$_4$)$_2$I, linking charge-density waves with Weyl semimetal topology through experimental and theoretical analysis.

Findings

(TaSe$_4$)$_2$I is a Weyl semimetal with 24 pairs of Weyl nodes.

The CDW couples Weyl points and opens a band gap.

The phase transition enables exploration of axion electrodynamics and topological responses.

Abstract

Topological physics and strong electron-electron correlations in quantum materials are typically studied independently. However, there have been rapid recent developments in quantum materials in which topological phase transitions emerge when the single-particle band structure is modified by strong interactions. We here demonstrate that the room-temperature phase of (TaSe$_4$)$_2$I is a Weyl semimetal with 24 pairs of Weyl nodes. Owing to its quasi-1D structure, (TaSe$_4$)$_2$I hosts an established CDW instability just below room temperature. Using X-ray diffraction, angle-resolved photoemission spectroscopy, and first-principles calculations, we find that the CDW in (TaSe$_4$)$_2$I couples the bulk Weyl points and opens a band gap. The correlation-driven topological phase transition in (TaSe$_4$)$_2$I provides a route towards observing condensed-matter realizations of axion electrodynamics in the gapped regime, topological chiral response effects in the semimetallic phase, and represents an avenue for exploring the interplay of correlations and topology in a solid-state material.