title: Weak Topological Insulators and Composite Weyl Semimetals: β-Bi4X4 (X=Br, I).
abstract: While strong topological insulators (STIs) were experimentally realized soon after they were theoretically predicted, a weak topological insulator (WTI) has yet to be unambiguously confirmed. A major obstacle is the lack of distinct natural cleavage surfaces to test the surface selective hallmark of a WTI. With a new scheme, we discover that β-Bi4X4 (X=Br, I), dynamically stable or synthesized before, can be a prototype WTI with two natural cleavage surfaces, where two anisotropic Dirac cones stabilize and annihilate, respectively. We further find four surface-state Lifshitz transitions under charge doping and two bulk topological phase transitions under uniaxial strain. Near the WTI-STI transition, there emerges a novel Weyl semimetal phase, in which the Fermi arcs generically appear at both cleavage surfaces whereas the Fermi circle only appears at one selected surface.
authors.affiliation: Department of Physics, University of Texas at Dallas, Richardson, Texas 75080, USA.|School of Physics, Beijing Institute of Technology, Beijing 100081, China.
authors.forename: Cheng-Cheng
authors.initials: CC
authors.lastname: Liu
authors.affiliation: School of Physics, Beijing Institute of Technology, Beijing 100081, China.
authors.forename: Jin-Jian
authors.initials: JJ
authors.lastname: Zhou
authors.affiliation: School of Physics, Beijing Institute of Technology, Beijing 100081, China.
authors.forename: Yugui
authors.initials: Y
authors.lastname: Yao
authors.affiliation: Department of Physics, University of Texas at Dallas, Richardson, Texas 75080, USA.
authors.forename: Fan
authors.initials: F
authors.lastname: Zhang