Quantum Spin Hall States in 2D Bismuth-Based Materials

Kapitel i bok, 2019

Berrys phase, an inherent constituent of the electronic wave functions, has revolutionarily enriched our understanding of the fundamental states of matter and has triggered the discovery of many interesting phenomena in condensed matter physics, such as quantum charge/spin pumping, polarization, topological insulating phase, etc. Among them, the discovery of the two-dimensional (2D) quantum spin Hall (QSH) states protected by time-reversal symmetry (TRS) boosts the wide interest in the study of topological materials in the past decade. These include the 2D quantum anomalous Hall states (QAH), three-dimensional topological insulators (TIs), Dirac semimetals (SM), and topological nodal-line SMs as well as Weyl SMs. This article by no means can cover everything of this rapidly developing field, we rather focus on the bismuth-based honeycomb materials hosting large-gap QSH/QAH states, which promise applications for room-temperature spintronic. We will explain their topological mechanisms in terms of Berrys phase and topological invariant. After introducing a concrete material example which has been successfully grown in experiment, e.g., Bi/SiC(0001), various theoretical proposals on atom substitution and functionalization based on bismuth honeycomb lattice will then be discussed, from which a general designing principle for achieving large topological gaps can be summarized. This article hopes to stimulate more experimental activities toward the examination of large-gap QSH/QAH theoretical proposals and the potential applications in spintronic devices.