Fig. 1: Topological properties and crystal structures of α/β-Bi4I4.
From: Topological phase transition in quasi-one-dimensional bismuth iodide Bi4I4
a The crystal structure of α-Bi4I4. The black lines indicate the unit cell. b Schematic illustration of the boundary states on the (100) surfaces. Each dot represents the QSH edge state of a Bi4I4 monolayer. The yellow-dot pair in an ellipse and red dots represent the quantum-hybridized (100) surface states and the topological hinge states, respectively. c Illustration of the electronic structure of α-Bi4I4 on the (100) side surface. The gray, yellow, and red curves indicate the bulk, surface, and hinge states, respectively. d–f The same as (a–c) except for β-Bi4I4. The green dots in (e) and green curves in (f) represent the topological surface states on the (100) surface of β-Bi4I4. g Cross-section image of the (010) surface of α-Bi4I4 with atomic resolution measured with scanning transmission electron microscope (STEM). h X-ray diffraction measurements of α-Bi4I4. The STEM and XRD measurements are performed at 298 K.
