Nonsymmorphic symmetry protected node-line semimetal in the trigonal YH3

TL;DR

This paper predicts that trigonal YH3 is a nodal-line semimetal protected by glide-plane symmetry without spin-orbit coupling, and becomes a topological insulator with a small SOC-induced gap, making it a promising candidate for experimental study.

Contribution

It demonstrates that YH3's nodal lines are protected by glide-plane symmetry and explores the effects of spin-orbit coupling, revealing a transition to a topological insulator.

Findings

YH3 is a near-Fermi-level nodal-line semimetal without SOC.

SOC opens a small gap, turning YH3 into a strong topological insulator.

Surface states of YH3 are unique and experimentally detectable.

Abstract

Using ab initio calculations based on density-functional theory and effective model analysis, we propose that the trigonal YH3(Space Group: P-3c1) at ambient pressure is a node-line semimetal when spin-orbit coupling (SOC) is ignored. This trigonal YH3 has very clean electronic structure near Fermi level and its nodal lines locate very closely to the Fermi energy, which makes it a perfect system for model analysis. Symmetry analysis shows that the nodal ring in this compound is protected by the glide-plane symmetry, where the band inversion of |Y+,dxz> and |H1-,s> orbits at Gamma point is responsible for the formation of the nodal lines. When SOC is included, the line nodes are prohibited by the glide-plane symmetry, and a small gap (~5 meV) appears, which leads YH3 to be a strong topological insulator with Z2 indices (1,000). Thus the glide-plane symmetry plays an opposite role in the formation of the nodal lines in cases without and with SOC. As the SOC-induced gap is so small that can be neglected, this P-3c1 YH3 may be a good candidate for experimental explorations on the fundamental physics of topological node-line semimetals. We find the surface states of this P-3c1 phase are somehow unique and may be helpful to identify the real ground state of YH3 in the experiment.