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Coexistence of type-I and type-II nodal lines in monolayer TiBF
Solid State Communications ( IF 2.1 ) Pub Date : 2020-04-01 , DOI: 10.1016/j.ssc.2020.113839 Jie Shang , Yu Liang , Liu Yang , Jianwei Li , Dong Liang
Solid State Communications ( IF 2.1 ) Pub Date : 2020-04-01 , DOI: 10.1016/j.ssc.2020.113839 Jie Shang , Yu Liang , Liu Yang , Jianwei Li , Dong Liang
Abstract Topological nodal line semimetals with protected 1-D Fermi lines have continuously attracted great interest. In this study, based on first-principles calculations, we demonstrate that type-I and type-II nodal lines can coexist in the dynamically stable monolayer TiBF. Both types of nodal lines are protected by mirror symmetry in the absence of spin-orbital coupling. Besides, we find that the closed nodal lines can be effectively tuned by applying biaxial tensile strain. Interestingly, with a moderate compressive biaxial strain, a novel metal-semimetal-semiconductor phase transition can be induced, during which a 2-D double Weyl fermion emerges. The 2-D double Weyl fermion features a single Fermi point, where the conduction and the valence bands contact quadratically. We construct an effective Hamiltonian to characterize the 2-D double Weyl fermion. Additionally, we show that TiBX (X = Cl, Br, I) monolayers possess similar properties. Our findings show that the monolayer TiBF is a fascinating platform to investigate unique topological phases and that it demonstrates a great potential for nanoscale device applications.
更新日期：2020-04-01
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