title: Spin-orbit-free topological insulators without time-reversal symmetry.
abstract: We explore the 32 crystallographic point groups and identify topological phases of matter with robust surface modes. For n=3,4, and 6 of the C_{nv} groups, we find the first-known 3D topological insulators without spin-orbit coupling, and with surface modes that are protected only by point groups; i.e., the relevant symmetries are purely crystalline and do not include time reversal. To describe these C_{nv} systems, we introduce the notions of (a) a halved mirror chirality, an integer invariant which characterizes half-mirror-planes in the 3D Brillouin zone, and (b) a bent Chern number, the traditional Thouless-Kohmoto-Nightingale-den Nijs invariant generalized to bent 2D manifolds. We find that a Weyl semimetallic phase intermediates two gapped phases with distinct halved chiralities. In addition to electronic systems without spin-orbit coupling, our findings also apply to intrinsically spinless systems such as photonic crystals and ultracold atoms.
authors.affiliation: Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: A
authors.initials: A
authors.lastname: Alexandradinata
authors.affiliation: Department of Physics, Princeton University, Princeton, New Jersey 08544, USA and Department of Physics, University of Illinois, Urbana, Illinois 61801, USA and Micro and Nanotechnology Laboratory, University of Illinois, 208 N. Wright Street, Urbana, Illinois 61801, USA.
authors.forename: Chen
authors.initials: C
authors.lastname: Fang
authors.affiliation: Micro and Nanotechnology Laboratory, University of Illinois, 208 N. Wright Street, Urbana, Illinois 61801, USA and Department of Electrical and Computer Engineering, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Gilbert
authors.affiliation: Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: B Andrei
authors.initials: BA
authors.lastname: Bernevig