title: Topological nodal-line fermions in spin-orbit metal PbTaSe2.
abstract: Topological semimetals can support one-dimensional Fermi lines or zero-dimensional Weyl points in momentum space, where the valence and conduction bands touch. While the degeneracy points in Weyl semimetals are robust against any perturbation that preserves translational symmetry, nodal lines require protection by additional crystalline symmetries such as mirror reflection. Here we report, based on a systematic theoretical study and a detailed experimental characterization, the existence of topological nodal-line states in the non-centrosymmetric compound PbTaSe2 with strong spin-orbit coupling. Remarkably, the spin-orbit nodal lines in PbTaSe2 are not only protected by the reflection symmetry but also characterized by an integer topological invariant. Our detailed angle-resolved photoemission measurements, first-principles simulations and theoretical topological analysis illustrate the physical mechanism underlying the formation of the topological nodal-line states and associated surface states for the first time, thus paving the way towards exploring the exotic properties of the topological nodal-line fermions in condensed matter systems.
authors.affiliation: Department of Physics, Laboratory for Topological Quantum Matter and Spectroscopy (B7), Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Guang
authors.initials: G
authors.lastname: Bian
authors.affiliation: Department of Physics, Laboratory for Topological Quantum Matter and Spectroscopy (B7), Princeton University, Princeton, New Jersey 08544, USA.|Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan.
authors.forename: Tay-Rong
authors.initials: TR
authors.lastname: Chang
authors.affiliation: Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan.
authors.forename: Raman
authors.initials: R
authors.lastname: Sankar
authors.affiliation: Department of Physics, Laboratory for Topological Quantum Matter and Spectroscopy (B7), Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Su-Yang
authors.initials: SY
authors.lastname: Xu
authors.affiliation: Department of Physics, Laboratory for Topological Quantum Matter and Spectroscopy (B7), Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Hao
authors.identifier: http://orcid.org/0000-0002-6495-874X
authors.initials: H
authors.lastname: Zheng
authors.affiliation: Department of Physics, Laboratory for Topological Quantum Matter and Spectroscopy (B7), Princeton University, Princeton, New Jersey 08544, USA.|Princeton Center for Theoretical Science, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Titus
authors.identifier: http://orcid.org/0000-0003-0604-041X
authors.initials: T
authors.lastname: Neupert
authors.affiliation: Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1.
authors.forename: Ching-Kai
authors.initials: CK
authors.lastname: Chiu
authors.affiliation: Centre for Advanced 2D Materials and Graphene Research Centre National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore.|Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore.
authors.forename: Shin-Ming
authors.identifier: http://orcid.org/0000-0003-4273-9682
authors.initials: SM
authors.lastname: Huang
authors.affiliation: Centre for Advanced 2D Materials and Graphene Research Centre National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore.|Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore.
authors.forename: Guoqing
authors.identifier: http://orcid.org/0000-0003-1180-3127
authors.initials: G
authors.lastname: Chang
authors.affiliation: Department of Physics, Laboratory for Topological Quantum Matter and Spectroscopy (B7), Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Ilya
authors.initials: I
authors.lastname: Belopolski
authors.affiliation: Department of Physics, Laboratory for Topological Quantum Matter and Spectroscopy (B7), Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Sanchez
authors.affiliation: Department of Physics, Laboratory for Topological Quantum Matter and Spectroscopy (B7), Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Madhab
authors.initials: M
authors.lastname: Neupane
authors.affiliation: Department of Physics, Laboratory for Topological Quantum Matter and Spectroscopy (B7), Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Nasser
authors.initials: N
authors.lastname: Alidoust
authors.affiliation: Department of Physics, Laboratory for Topological Quantum Matter and Spectroscopy (B7), Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Chang
authors.initials: C
authors.lastname: Liu
authors.affiliation: Centre for Advanced 2D Materials and Graphene Research Centre National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore.|Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore.|Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: BaoKai
authors.identifier: http://orcid.org/0000-0002-7221-5671
authors.initials: B
authors.lastname: Wang
authors.affiliation: Centre for Advanced 2D Materials and Graphene Research Centre National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore.|Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore.
authors.forename: Chi-Cheng
authors.initials: CC
authors.lastname: Lee
authors.affiliation: Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan.|Institute of Physics, Academia Sinica, Taipei 11529, Taiwan.
authors.forename: Horng-Tay
authors.initials: HT
authors.lastname: Jeng
authors.affiliation: ICQM, School of Physics, Peking University, Beijing 100871, China.
authors.forename: Chenglong
authors.initials: C
authors.lastname: Zhang
authors.affiliation: ICQM, School of Physics, Peking University, Beijing 100871, China.
authors.forename: Zhujun
authors.identifier: http://orcid.org/0000-0003-1793-1461
authors.initials: Z
authors.lastname: Yuan
authors.affiliation: ICQM, School of Physics, Peking University, Beijing 100871, China.
authors.forename: Shuang
authors.initials: S
authors.lastname: Jia
authors.affiliation: Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: Arun
authors.initials: A
authors.lastname: Bansil
authors.affiliation: Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan.
authors.forename: Fangcheng
authors.initials: F
authors.lastname: Chou
authors.affiliation: Centre for Advanced 2D Materials and Graphene Research Centre National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore.|Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore.
authors.forename: Hsin
authors.initials: H
authors.lastname: Lin
authors.affiliation: Department of Physics, Laboratory for Topological Quantum Matter and Spectroscopy (B7), Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: M Zahid
authors.initials: MZ
authors.lastname: Hasan
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