Topological nodal lines and hybrid Weyl nodes in YCoC2

Yuanfeng Xu,Xian-Lei Sheng,Hongming Weng,Tiantian Zhang,Yueqiang Gu,Chen Fang,Zhong Fang

doi:10.1063/1.5123222

Abstract

Based on first-principles calculations and effective model analysis, we propose that the noncentrosymmetric superconductor YCoC2 in normal state is a topological semimetal. In the absence of spin-orbit coupling (SOC), it can host two intersecting nodal rings protected by two mirror planes, respectively. One ring is composed of type-I nodes, where the two crossing bands have opposite slope sign in their dispersions. The other ring consists of both type-I and type-II nodes (the slope signs of the two bands are the same in certain direction). In the presence of SOC, the former nodal ring is gapped totally while the latter one evolves into ten pairs of Weyl nodes, with two of them being type-I and eight being type-II. The type-II Weyl nodes are further classified into two kinds with different velocity matrices when described in Weyl equation near the nodes. Fermi arcs from topological surface states are observed in the surface projected energy dispersions. It is notable that YCoC2 has been reported as a superconductor with a critical temperature Tc of 4.2 K. This makes it very attractive since including superconducting into a topological semimetal state might result in topological superconductivity and be used to synthesize Majorana zero modes.

Highlights

Topological quantum states and topological materials have attracted great interest from researchers in both fields of condensed matter physics and materials sciences
Based on first-principles calculations and effective model analysis, we propose that the noncentrosymmetric superconductor YCoC2 in normal state is a topological semimetal
In the absence of spin-orbit coupling (SOC), it can host two intersecting nodal rings protected by two mirror planes, respectively

Summary

INTRODUCTION

Topological quantum states and topological materials have attracted great interest from researchers in both fields of condensed matter physics and materials sciences. In recent years, the research focus has been shifted toward topological semimetals/metals.5–9 In these materials, the electronic band structure has the feature that there are energy nodes formed by band crossing close enough to the Fermi level, and these bands dominate the Fermi surface so that they possess topologically nontrivial properties. The bands cross along a 1D path in the momentum space, and the resulted drumhead surface states can be observed. Dirac fermions has been proposed and observed in Na3Bi54,55 and Cd3As2.56–59 For nodal line semimetals, they are first predicted in carbon network materials with three intersecting nodal rings.. The Fermi arc surface states connecting the projected Weyl points with opposite chirality have been discussed

CRYSTAL STRUCTURE AND METHODOLOGY

IN THE ABSENCE OF SOC

IN THE PRESENCE OF SOC

CONCLUSION