Topological Phase Transition and Texture Inversion in a Tunable Topological Insulator

• Published in: Science (American Association for the Advancement of Science) Vol. 332; no. 6029; pp. 560 - 564
• Main Authors: Xu, Su-Yang, Xia, Y., Wray, L. A., Jia, S., Meier, F., Dil, J. H., Osterwalder, J., Slomski, B., Bansil, A., Lin, H., Cava, R. J., Hasan, M. Z.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 29.04.2011; The American Association for the Advancement of Science
• Subjects: Binding energy; Carrier density; Chirality; Clean metal, semiconductor, and insulator surfaces; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron and ion emission by liquids and solids; impact phenomena; Electron density of states and band structure of crystalline solids; Electron states; electrons; Elementary excitations; Exact sciences and technology; Fermi surface: calculations and measurements; effective mass, g factor; Fermi surfaces; Insulators; Invariants; Inversions; Materials; Mathematical surfaces; Mathematical triviality; Other inorganic compounds; Phase transformations; phase transition; Photoemission and photoelectron spectra; Physics; Selenium; stereoisomerism; Sulfur; Surface layer; Surface texture; Texture; Topological vector spaces; Topology; Polarization; Energy levels; Quantum phase transition; Angle resolved photoemission spectroscopy; Bismuth Thallium Selenides sulfides Mixed; Momentum; Texture; Topological insulator; Chirality; Spin-orbit interactions; Chemical composition; Fermi surface; Spin state
• ISSN: 0036-8075; 1095-9203; 1095-9203
• DOI: 10.1126/science.1201607

The recently discovered three-dimensional or bulk topological insulators are expected to exhibit exotic quantum phenomena. It is believed that a trivial insulator can be twisted into a topological state by modulating the spin-orbit interaction or the crystal lattice, driving the system through a topological quantum phase transition. By directly measuring the topological quantum numbers and invariants, we report the observation of a phase transition in a tunable spin-orbit system, BiTl(S₁— δ Se δ )₂, in which the topological state formation is visualized. In the topological state, vortex-like polarization states are observed to exhibit three-dimensional vectorial textures, which collectively feature a chirality transition as the spin momentum—locked electrons on the surface go through the zero carrier density point. Such phase transition and texture inversion can be the physical basis for observing fractional charge (±e/2) and other fractional topological phenomena.