Kramers-Weyl fermions in the chiral charge density wave material (TaSe$_4$)$_2$I

TL;DR

This study provides direct spectroscopic evidence of Kramers-Weyl fermions in the chiral charge density wave material (TaSe4)2I, revealing their topological nature and interplay with charge density wave order through advanced ARPES and theoretical calculations.

Contribution

First direct identification of Kramers-Weyl fermions in (TaSe4)2I using helicity-dependent ARPES and theoretical modeling, highlighting their topological characteristics and relation to charge density waves.

Findings

Identification of Kramers-Weyl fermions near high symmetry points.

Observation of spin texture interplay with charge density wave order.

Confirmation of topological constraints on spectra around KW nodes.

Abstract

The quasi-one-dimensional chiral charge density wave (CDW) material (TaSe$_4$)$_2$I has been recently predicted to host Kramers-Weyl (KW) fermions which should exist in the vicinity of high symmetry points in the Brillouin zone in chiral materials with strong spin-orbit coupling. However, direct spectroscopic evidence of KW fermions is limited. Here we use helicity-dependent laser-based angle resolved photoemission spectroscopy (ARPES) in conjunction with tight-binding and first-principles calculations to identify KW fermions in (TaSe$_4$)$_2$I. We find that topological and symmetry considerations place distinct constraints on the (pseudo-) spin texture and the observed spectra around a KW node. We further reveal an interplay between the spin texture around the chiral KW node and the onset of CDW order in (TaSe$_4$)$_2$I. Our findings highlight the unique topological nature of (TaSe$_4$)$_2$I and provide a pathway for identifying KW fermions in other chiral materials.