Rich topological nodal line bulk states together with drum-head-like surface states in NaAlGe with anti-PbFCl type structure

Xiaotian Wang,Guangqian Ding,Zhenxiang Cheng,Gokhan Surucu,Xiao-Lin Wang,Tie Yang

doi:10.1016/j.jare.2020.01.017

Abstract

The band topology in condensed matter has attracted widespread attention in recent years. Due to the band inversion, topological nodal line semimetals (TNLSs) have band crossing points (BCPs) around the Fermi level, forming a nodal line. In this work, by means of first-principles, we observe that the synthesized NaAlGe intermetallic compound with anti-PbFCl type structure is a TNLS with four NLs in the kz = 0 and kz = π planes. All these NLs in NaAlGe exist around the Fermi level, and what is more, these NLs do not overlap with other bands. The exotic drum-head-like surface states can be clearly observed, and therefore, the surface characteristics of NaAlGe may more easily be detected by experiments. Biaxial strain has been explored for this system, and our results show that rich TNL states can be induced. Furthermore, the spin-orbit coupling effect has little effect on the band structure of NaAlGe. It is hoped that this unique band structure can soon be examined by experimental work and that its novel topological elements can be fully explored for electronic devices.

Highlights

Topological insulators [1,2,3,4,5] have been the hotspot of modern condensed matter physics for several years
According to the degeneracy of band crossing points (BCPs) and their distribution in the Brillouin zone, topological semimetals (TSMs) can be classified into the following types: Dirac semimetals [26,27,28], Weyl semimetals [29,30], and topological nodal line semimetals (TNLS) [31]
We can conclude that such BCPs cannot be seen as isolated nodal points [51,53] when the role of the SOC is not taken into account

Summary

Introduction

Topological insulators [1,2,3,4,5] have been the hotspot of modern condensed matter physics for several years. According to the degeneracy of band crossing points (BCPs) and their distribution in the Brillouin zone, TSMs can be classified into the following types: Dirac semimetals [26,27,28], Weyl semimetals [29,30], and topological nodal line semimetals (TNLS) [31]. Different from the isolated points in the Dirac and Weyl semimetals, for a TNLS, the crossings between the bands can form one-dimensional (1D) nodal lines (NLs)/loops in three-dimensional (3D) momentum space under certain crystal symmetries. The physical properties of type I, type II, and hybrid type TSMs are quite different [35,36]

Methods

Results

Conclusion