Triply degenerate nodal points in RERh$_{6}$Ge$_{4}$ (RE=Y, La, Lu)

TL;DR

This paper predicts a new class of topological semimetals with triply degenerate nodal points at symmetric axes, specifically RERh6Ge4 compounds, using space group theory and first-principles calculations, highlighting their potential for studying exotic physics.

Contribution

The paper introduces a practical guidance for identifying triply degenerate nodal points in topological semimetals and predicts RERh6Ge4 compounds as candidates with such features.

Findings

Triply degenerate nodal points are predicted at the Γ-A axis.

LaRh6Ge4 has nodal points near the Fermi level.

The compounds are experimentally synthesizable.

Abstract

As a new type of fermions without counterpart in high energy physics, triply degenerate fermions show exotic physical properties, which are represented by triply degenerate nodal points in topological semimetals. Here, based on the space group theory analysis, we propose a practical guidance for seeking a topological semimetal with triply degenerate nodal points located at a symmetric axis, which is applicable to both symmorphic and nonsymmorphic crystals. By using this guidance in combination with the first-principles electronic structure calculations, we predict a class of triply degenerate topological semimetals RERh$_{6}$Ge$_{4}$ (RE=Y, La, Lu). In these compounds, the triply degenerate nodal points are located at the $\Gamma$-A axis and not far from the Fermi level. Especially, LaRh$_{6}$Ge$_{4}$ has a pair of triply degenerate nodal points located very closely to the Fermi level. Considering the fact that the single crystals of RERh$_{6}$Ge$_{4}$ have been synthesized experimentally, the RERh$_{6}$Ge$_{4}$ class of compounds will be an appropriate platform for studying exotic physical properties of triply degenerate topological semimetals.