Unexpected Dirac-Node Arc in the Topological Line-Node Semimetal HfSiS

TL;DR

This study uses angle-resolved photoemission spectroscopy to reveal a novel Dirac-node arc in HfSiS, a topological line-node semimetal, highlighting unexpected surface states that challenge existing theoretical models.

Contribution

It reports the discovery of a unique Dirac-node arc in HfSiS, expanding understanding of surface states in topological line-node semimetals.

Findings

Discovery of a Dirac-node arc near the bulk node

Observation of surface states with Rashba splitting

Identification of many-body interaction effects

Abstract

We have performed angle-resolved photoemission spectroscopy on HfSiS, which has been predicted to be a topological line-node semimetal with square Si lattice. We found a quasi-two-dimensional Fermi surface hosting bulk nodal lines, alongside the surface states at the Brillouin-zone corner exhibiting a sizable Rashba splitting and band-mass renormalization due to many-body interactions. Most notably, we discovered an unexpected Dirac-like dispersion extending one-dimensionally in k space - the Dirac-node arc - near the bulk node at the zone diagonal. These novel Dirac states reside on the surface and could be related to hybridizations of bulk states, but currently we have no explanation for its origin. This discovery poses an intriguing challenge to the theoretical understanding of topological line-node semimetals.