Topological Triply Degenerate Points Induced by Spin-Tensor-Momentum Couplings

TL;DR

This paper explores how spin-tensor- and spin-vector-momentum couplings can induce various topological triply degenerate points (TDPs) with different monopole charges, and proposes an experimental realization in cold-atom systems.

Contribution

It introduces a new mechanism for creating TDPs via combined spin-tensor- and spin-vector-momentum couplings and classifies them by monopole charge, expanding the understanding of topological quasiparticles.

Findings

Three types of TDPs with monopole charges $\u2113=\u2212 2,\u2212 1,0$ are induced.

Zeeman field can transform TDPs into Weyl points with specific charges.

Surface Fermi arcs connect different TDP types, and phase transitions involve level crossings.

Abstract

The recent discovery of triply degenerate points (TDPs) in topological materials has opened a new perspective toward the realization of novel quasiparticles without counterparts in quantum field theory. The emergence of such protected nodes is often attributed to spin-vector-momentum couplings. Here we show that the interplay between spin-tensor- and spin-vector-momentum couplings can induce three types of TDPs, classified by different monopole charges ($\mathcal{C}=\pm 2,\pm 1,0$). A Zeeman field can lift them into Weyl points with distinct numbers and charges. Different TDPs of the same type are connected by intriguing Fermi arcs at surfaces, and transitions between different types are accompanied by level crossings along high-symmetry lines. We further propose an experimental scheme to realize such TDPs in cold-atom optical lattices. Our results provide a framework for studying spin-tensor-momentum coupling-induced TDPs and other exotic quasiparticles.