Topological semimetals with nodal-rings and nexus fermions

TL;DR

This paper predicts new topological semimetals with unique nodal-ring and nexus fermion features, supported by first-principles calculations and ARPES simulations, revealing potential for quantum transport applications.

Contribution

It introduces a new class of topological semimetals exhibiting co-existing nodal-rings and triply-degenerate points, including the novel nexus fermions.

Findings

Identification of materials with co-existing nodal-rings and triply-degenerate points.

Simulation of surface states and Fermi arcs via ARPES.

Analysis of spin-orbit coupling effects on triple-points.

Abstract

Based on the first-principles study, we report a new set of topological semimetals (TiS, TiSe, TiTe, HfS, HfSe, HfTe and ZrS) which show the co-existence of a nodal-ring and triply-degenerate points. The two-fold degenerate one-dimensional nodal ring structure in the bulk Brillouin zone exhibits the characteristic drumhead surface states. In addition to this, a peculiar band crossing along the $k_z$ direction takes place consisting of a point-crossing with three-fold band degeneracy. These triply-degenerate points give rise to "nexus" fermions as quasiparticles having no analogous elementary particle of the standard model. In this article, we simulate angle-resolved photoemission spectroscopy to obtain the exotic topological surface states and the characteristic Fermi arcs, and explain the evolution and separation of triple-points with the magnitude of spin-orbit coupling. This intermediate linearly dispersive degeneracy between Weyl and Dirac points may offer prospective candidates for quantum transport applications.