Signatures of a topological Weyl loop in Co$_3$Sn$_2$S$_2$

TL;DR

This study uses ARPES to identify signatures of a topological Weyl loop in Co$_3$Sn$_2$S$_2$, highlighting the challenges in conclusively detecting Weyl points and Fermi arcs due to experimental limitations.

Contribution

First ARPES investigation revealing signatures of a topological Weyl loop in Co$_3$Sn$_2$S$_2$, emphasizing the ambiguity in identifying Weyl points and Fermi arcs.

Findings

Signatures of a topological Weyl loop observed.

Weyl points and Fermi arcs remain ambiguous due to experimental limitations.

The presence of a Weyl loop in Co$_3$Sn$_2$S$_2$ is suggested but not conclusively proven.

Abstract

The search for novel topological phases of matter in quantum magnets has emerged as a frontier of condensed matter physics. Here we use state-of-the-art angle-resolved photoemission spectroscopy (ARPES) to investigate single crystals of Co$_3$Sn$_2$S$_2$ in its ferromagnetic phase. We report for the first time signatures of a topological Weyl loop. From fundamental symmetry considerations, this magnetic Weyl loop is expected to be gapless if spin-orbit coupling (SOC) is strictly zero but gapped, with possible Weyl points, under finite SOC. We point out that high-resolution ARPES results to date cannot unambiguously resolve the SOC gap anywhere along the Weyl loop, leaving open the possibility that Co$_3$Sn$_2$S$_2$ hosts zero Weyl points or some non-zero number of Weyl points. On the surface of our samples, we further observe a possible Fermi arc, but we are unable to clearly verify its topological nature using the established counting criteria. As a result, we argue that from the point of view of photoemission spectroscopy the presence of Weyl points and Fermi arcs in Co$_3$Sn$_2$S$_2$ remains ambiguous. Our results have implications for ongoing investigations of Co$_3$Sn$_2$S$_2$ and other topological magnets.