Photoemission Spectroscopic Evidence for the Dirac Nodal Line in Monoclinic Semimetal SrAs$_3$

TL;DR

This study provides experimental and theoretical evidence for Dirac nodal-line fermions in SrAs$_3$, a monoclinic semimetal, highlighting its potential as a platform for topological quantum research due to its simple bulk states near the Fermi level.

Contribution

The paper experimentally confirms the existence of Dirac nodal-line fermions in SrAs$_3$ and clarifies their topological nature, which was previously obscured by trivial states in similar materials.

Findings

Identification of a single nodal loop near the Fermi level in SrAs$_3$

Band inversion around Y point leads to the nodal line

SrAs$_3$ hosts simple topological states with minimal surface interference

Abstract

Topological nodal-line semimetals with exotic quantum properties are characterized by symmetry-protected line-contact bulk band crossings in the momentum space. However, in most of identified topological nodal-line compounds, these topological non-trivial nodal lines are enclosed by complicated topological trivial states at the Fermi energy ($E_F$), which would perplex their identification and hinder further applications. Utilizing angle-resolved photoemission spectroscopy and first-principles calculations, we provide compelling evidence for the existence of Dirac nodal-line fermions in the monoclinic semimetal SrAs$_3$, which are close to $E_F$ and away from distraction of complex trivial Fermi surfaces or surface states. Our calculation indicates that two bands with opposite parity are inverted around \emph{Y} near $E_F$, which results in the single nodal loop at the $\Gamma$-\emph{Y}-\emph{S} plane with a negligible spin-orbit coupling effect. We track these band crossings and then unambiguously identify the complete nodal loop quantitatively, which provides a critical experimental support to the prediction of nodal-line fermions in the CaP$_3$ family of materials. Hosting simple topological non-trivial bulk electronic states around $E_F$ and no interfering with surface states on the natural cleavage plane, SrAs$_3$ is expected to be a potential platform for topological quantum state investigation and applications.