title: Emergence of topological nodal loops in alkaline-earth hexaborides XB6(X = Ca, Sr, and Ba) under pressure.
abstract: Based on first-principles calculations, we report that external pressure can induce a topological phase transition in alkaline-earth hexaborides, XB6(X = Ca, Sr, and Ba). It was revealed that XB6are transformed from trivial semiconductors to topological node-line semimetals under moderate pressure when the spin-orbit coupling (SOC) is ignored. The band inversion between the B p-orbitals at the X point is responsible for the formation of node-line semimetals. Three node-line rings around the X point are protected by the combination of the time-reversal and spatial inversion symmetries, and drumhead surface bands are obtained in the interiors of the projected node-line rings. When the SOC is included, tiny gaps (<4.8 meV) open at the crossing lines and the XB6become strong topological insulators with Z2indices (1 : 111). As the SOC-induced gap opening is negligible, our findings thus suggest ideal real systems for experimental exploration of the fundamental physics of topological node-line semimetals.
authors.affiliation: Department of Physics, South University of Science and Technology of China, Shenzhen 518055, China. liujf@sustc.edu.cn xu.h@sustc.edu.cn and Key Laboratory of Advanced Technology of Materials (Ministry of Education), Superconductivity and New Energy R&D Center, Southwest Jiaotong University, Chengdu, 610031 Sichuan, China.
authors.forename: L-Y
authors.identifier: http://orcid.org/0000-0002-1879-1918
authors.initials: LY
authors.lastname: Gan
authors.affiliation: Department of Physics, South University of Science and Technology of China, Shenzhen 518055, China. liujf@sustc.edu.cn xu.h@sustc.edu.cn and Institute for Structure and Function & Department of Physics, Chongqing University, 400030 Chongqing, China.
authors.forename: R
authors.initials: R
authors.lastname: Wang
authors.affiliation: Department of Physics, South University of Science and Technology of China, Shenzhen 518055, China. liujf@sustc.edu.cn xu.h@sustc.edu.cn.
authors.forename: Y J
authors.initials: YJ
authors.lastname: Jin
authors.affiliation: Department of Physics, Anhui University, Hefei 230601, China.
authors.forename: D B
authors.initials: DB
authors.lastname: Ling
authors.affiliation: Department of Physics, South University of Science and Technology of China, Shenzhen 518055, China. liujf@sustc.edu.cn xu.h@sustc.edu.cn.
authors.forename: J Z
authors.initials: JZ
authors.lastname: Zhao
authors.affiliation: Department of Physics, South University of Science and Technology of China, Shenzhen 518055, China. liujf@sustc.edu.cn xu.h@sustc.edu.cn.
authors.forename: W P
authors.initials: WP
authors.lastname: Xu
authors.affiliation: Department of Physics, South University of Science and Technology of China, Shenzhen 518055, China. liujf@sustc.edu.cn xu.h@sustc.edu.cn.
authors.forename: J F
authors.initials: JF
authors.lastname: Liu
authors.affiliation: Department of Physics, South University of Science and Technology of China, Shenzhen 518055, China. liujf@sustc.edu.cn xu.h@sustc.edu.cn.
authors.forename: H
authors.identifier: http://orcid.org/0000-0002-2254-5840
authors.initials: H
authors.lastname: Xu