title: Unconventional transformation of spin Dirac phase across a topological quantum phase transition.
abstract: The topology of a topological material can be encoded in its surface states. These surface states can only be removed by a bulk topological quantum phase transition into a trivial phase. Here we use photoemission spectroscopy to image the formation of protected surface states in a topological insulator as we chemically tune the system through a topological transition. Surprisingly, we discover an exotic spin-momentum locked, gapped surface state in the trivial phase that shares many important properties with the actual topological surface state in anticipation of the change of topology. Using a spin-resolved measurement, we show that apart from a surface bandgap these states develop spin textures similar to the topological surface states well before the transition. Our results offer a general paradigm for understanding how surface states in topological phases arise from a quantum phase transition and are suggestive for the future realization of Weyl arcs, condensed matter supersymmetry and other fascinating phenomena in the vicinity of a quantum criticality.
authors.affiliation: Department of Physics, Joseph Henry Laboratory, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Su-Yang
authors.initials: SY
authors.lastname: Xu
authors.affiliation: Department of Physics, Joseph Henry Laboratory, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Madhab
authors.initials: M
authors.lastname: Neupane
authors.affiliation: Department of Physics, Joseph Henry Laboratory, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Ilya
authors.initials: I
authors.lastname: Belopolski
authors.affiliation: Department of Physics, Joseph Henry Laboratory, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Chang
authors.initials: C
authors.lastname: Liu
authors.affiliation: Department of Physics, Joseph Henry Laboratory, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Nasser
authors.initials: N
authors.lastname: Alidoust
authors.affiliation: Department of Physics, Joseph Henry Laboratory, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Guang
authors.initials: G
authors.lastname: Bian
authors.affiliation: 1] Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA [2] International Center for Quantum Materials, Peking University, Beijing 100871, China.
authors.forename: Shuang
authors.initials: S
authors.lastname: Jia
authors.affiliation: 1] Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen, Switzerland [2] Physik-Institute, Universitat Zurich-Irchel, CH-8057 Zurich, Switzerland.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Landolt
authors.affiliation: 1] Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen, Switzerland [2] Physik-Institute, Universitat Zurich-Irchel, CH-8057 Zurich, Switzerland.
authors.forename: Batosz
authors.initials: B
authors.lastname: Slomski
authors.affiliation: 1] Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen, Switzerland [2] Physik-Institute, Universitat Zurich-Irchel, CH-8057 Zurich, Switzerland [3] Institute of Condensed Matter Physics, Ecole Polytechnique Fédeérale de Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: J Hugo
authors.initials: JH
authors.lastname: Dil
authors.affiliation: Department of Physics, Joseph Henry Laboratory, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Pavel P
authors.identifier: 0000000272145706
authors.initials: PP
authors.lastname: Shibayev
authors.affiliation: Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: Susmita
authors.initials: S
authors.lastname: Basak
authors.affiliation: Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan.
authors.forename: Tay-Rong
authors.initials: TR
authors.lastname: Chang
authors.affiliation: 1] Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan [2] Institute of Physics, Academia Sinica, Taipei 11529, Taiwan.
authors.forename: Horng-Tay
authors.initials: HT
authors.lastname: Jeng
authors.affiliation: Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Cava
authors.affiliation: Graphene Research Centre and Department of Physics, National University of Singapore, Singapore 11754, Singapore.
authors.forename: Hsin
authors.initials: H
authors.lastname: Lin
authors.affiliation: Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: Arun
authors.initials: A
authors.lastname: Bansil
authors.affiliation: 1] Department of Physics, Joseph Henry Laboratory, Princeton University, Princeton, New Jersey 08544, USA [2] Princeton Center for Complex Materials, Princeton Institute for Science and Technology of Materials, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: M Zahid
authors.initials: MZ
authors.lastname: Hasan