title: A novel quasi-one-dimensional topological insulator in bismuth iodide β-Bi4I4.
abstract: Recent progress in the field of topological states of matter has largely been initiated by the discovery of bismuth and antimony chalcogenide bulk topological insulators (TIs; refs ,,,), followed by closely related ternary compounds and predictions of several weak TIs (refs ,,). However, both the conceptual richness of Z2 classification of TIs as well as their structural and compositional diversity are far from being fully exploited. Here, a new Z2 topological insulator is theoretically predicted and experimentally confirmed in the β-phase of quasi-one-dimensional bismuth iodide Bi4I4. The electronic structure of β-Bi4I4, characterized by Z2 invariants (1;110), is in proximity of both the weak TI phase (0;001) and the trivial insulator phase (0;000). Our angle-resolved photoemission spectroscopy measurements performed on the (001) surface reveal a highly anisotropic band-crossing feature located at the  point of the surface Brillouin zone and showing no dispersion with the photon energy, thus being fully consistent with the theoretical prediction.
authors.affiliation: Institute of Theoretical Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.|National Center for Computational Design and Discovery of Novel Materials MARVEL, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: Gabriel
authors.identifier: http://orcid.org/0000-0002-5265-8512
authors.initials: G
authors.lastname: Autès
authors.affiliation: Department of Chemistry and Food Chemistry, TU Dresden, D-01062 Dresden, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Isaeva
authors.affiliation: Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Luca
authors.initials: L
authors.lastname: Moreschini
authors.affiliation: Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: Jens C
authors.initials: JC
authors.lastname: Johannsen
authors.affiliation: Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: Andrea
authors.initials: A
authors.lastname: Pisoni
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.|Graduate Group in Applied Science and Technology, University of California, Berkeley, California 94720, USA.
authors.forename: Ryo
authors.initials: R
authors.lastname: Mori
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.|Department of Physics, University of California, Berkeley, California 94720, USA.
authors.forename: Wentao
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1-3, GSP-1, 119991 Moscow, Russian Federation.
authors.forename: Taisia G
authors.initials: TG
authors.lastname: Filatova
authors.affiliation: Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1-3, GSP-1, 119991 Moscow, Russian Federation.
authors.forename: Alexey N
authors.initials: AN
authors.lastname: Kuznetsov
authors.affiliation: Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: László
authors.initials: L
authors.lastname: Forró
authors.affiliation: Experimental Physics, Ulm University, Albert-Einstein-Allee 11, D-89081 Ulm, Germany.
authors.forename: Wouter
authors.initials: W
authors.lastname: Van den Broek
authors.affiliation: Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.|Institute of Physics and Applied Physics, Yonsei University, Seoul 120-749, Korea.
authors.forename: Yeongkwan
authors.initials: Y
authors.lastname: Kim
authors.affiliation: Departement of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea.|Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang 790-784, Korea.
authors.forename: Keun Su
authors.initials: KS
authors.lastname: Kim
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.|Department of Physics, University of California, Berkeley, California 94720, USA.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Lanzara
authors.affiliation: Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Denlinger
authors.affiliation: Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Eli
authors.initials: E
authors.lastname: Rotenberg
authors.affiliation: Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Aaron
authors.initials: A
authors.lastname: Bostwick
authors.affiliation: Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: Marco
authors.initials: M
authors.lastname: Grioni
authors.affiliation: Institute of Theoretical Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.|National Center for Computational Design and Discovery of Novel Materials MARVEL, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: Oleg V
authors.identifier: http://orcid.org/0000-0001-7281-3199
authors.initials: OV
authors.lastname: Yazyev