Designing Topological Phase of Bismuth Halides and Controlling Rashba Effect in Films Studied by ARPES

This book presents the observation and the control of spin-polarized electrons in Rashba thin films and topological insulators, including the first observations of a weak topological insulator (WTI) and a higher-order topological insulator (HOTI) in bismuth halides. It begins with a general review of electronic structures at the solid surface and mentions that an electron spin at a surface is polarized due to the Rashba effect or topological insulator states with strong spin-orbit coupling. Subsequently it describes the experimental techniques used to study these effects, that is, angle-resolved photoemission spectroscopy (ARPES). Further it moves its focus onto the experimental investigations, in which mainly two different systems—noble metal thin films with the Rashba effects and bismuth halides topological insulators—are used. The study of the first system discusses the role of wavefunctions in spin-splitting and demonstrates a scaling law for the Rashba effect in quantum well films for the first time. High-resolution spin-resolved ARPES plays a vital role in systematically trace the thickness-evolution of the effect. The study of the latter material is the first experimental demonstration of both a WTI and HOTI state in bismuth iodide and bismuth bromide, respectively. Importantly, nano-ARPES with high spatial resolution is used to confirm the topological surface states on the side surface of the crystal, which is the hallmark of WTIs.

The description of the basic and recently-developed ARPES technique with spin-resolution or spatial-resolution, essential in investigating spin-polarized electrons at a crystal surface, makes the book a valuable source for researchers not only in surface physics or topological materials but also in spintronics and other condensed-matter physics.

Ryo Noguchi, a postdoctoral scholar at the Department of Physics, the California Institute of Technology in the USA, is an experimentalist in materials sciences and surface physics. His work is concerned with novel quantum phenomena induced by spin-orbit coupling, such as the Rashba effect and topological insulators. He is particularly interested in observing and manipulating spin-polarized electrons through thin-film growth or stacking-dependence of layered materials and investigates them by angle-resolved photoemission spectroscopy (ARPES).

Ryo Noguchi received his Bachelor of Physics from The University of Tokyo in 2016, and thereafter he joined the group led by Professor Takeshi Kondo at the Institute for Solid State Physics (ISSP), The University of Tokyo, and received his Master and Doctor of Science in physics in 2018 and 2021, respectively. During his doctoral program, he received student presentation awards from the Physical Society of Japan, the Japanese Society forSynchrotron Radiation Research and the Japan Society of Vacuum and Surface Science, and The University of Tokyo President’s Award. He was also awarded a research fellowship for young scientists from the Japan Society for the Promotion of Science (JSPS), and his research was supported by JSPS between April 2018 and March 2021.