Suppression of axionic charge density wave and onset of superconductivity in the chiral Weyl semimetal Ta$_2$Se$_8$I

TL;DR

This study explores how pressure suppresses the axionic charge density wave in Ta$_2$Se$_8$I, leading to the emergence of superconductivity, and maps its topological phase diagram revealing the material's potential for studying correlated topological states.

Contribution

It demonstrates the suppression of the axionic CDW and the induction of superconductivity in Ta$_2$Se$_8$I through pressure, providing a comprehensive phase diagram of its topological states.

Findings

Suppression of CDW with pressure up to 17 GPa.

Induction of superconductivity due to iodine sub-lattice amorphization.

Complete topological phase diagram of Ta$_2$Se$_8$I.

Abstract

A Weyl semimetal with strong electron-phonon interaction can show axionic coupling in its insulator state at low temperatures, owing to the formation of a charge density wave (CDW). Such a CDW emerges in the linear chain compound Weyl semimetal Ta$_2$Se$_8$I below 263 K, resulting in the appearance of the dynamical condensed-matter axion quasiparticle. In this study, we demonstrate that the interchain coupling in Ta$_2$Se$_8$I can be varied to suppress the CDW formation with pressure, while retaining the Weyl semimetal phase at high temperatures. Above 17 GPa, the Weyl semimetal phase does not survive and we induce superconductivity, due to the amorphization of the iodine sub-lattice. Structurally, the one-dimensional Ta-Se-chains remain intact and provide a superconducting channel in one dimension. We highlight that our results show a near-complete suppression of the gap induced by the axionic charge-density wave at pressures inaccessible to previous studies. Including this CDW phase, our experiments and theoretical predictions and analysis reveal the complete topological phase diagram of Ta$_2$Se$_8$I and its relationship to the nearby superconducting state. The results demonstrate Ta$_2$Se$_8$I to be a distinctively versatile platform for exploring correlated topological states.