Triple point semimetal and topological phase transitions in NaCu$_{3}$Te$_{2}$

TL;DR

This paper predicts that NaCu$_{3}$Te$_{2}$ hosts triply degenerate nodal points and exhibits a tunable topological phase transition between these points and a weak topological insulator, highlighting its potential for studying exotic fermions.

Contribution

The study identifies NaCu$_{3}$Te$_{2}$ as a new material hosting triply degenerate nodal points and explores the topological phase transitions influenced by symmetry and spin-orbit coupling.

Findings

NaCu$_{3}$Te$_{2}$ hosts triply degenerate nodal points separated from bulk states.

A tunable phase transition exists between TDNPs and a weak topological insulator.

Spin-orbit coupling is crucial for the emergence of TDNPs in this system.

Abstract

Quasiparticle excitations of free electrons in condensed-matter physics, characterized by the dimensionality of the band crossing, can find their elementary-particle analogs in high-energy physics, such as Majorana, Weyl, and Dirac fermions. While crystalline symmetry allows more quasiparticle excitations and exotic fermions to emerge. Using symmetry analysis and {\it ab-initio} calculations, we propose that the 3D honeycomb crystal NaCu$_3$Te$_2$ hosts triply degenerate nodal points (TDNPs) which are perfectly separated from the bulk states. We find a tunable phase transition between TDNPs and a weak TI triggered by a symmetry-allowed perturbation, and we further reveal the crucial role played by the spin-orbital coupling (SOC) for the emergence of the TDNPs in this system. Such topological non-trivial ternary compound not only serves as a perfect candidate for studying three-component fermions, but also provides a beautiful playground for understanding the topological phase transitions between TDNPs, TIs and trivial insulators, which distinguishes this system from other TDNP candidates.