Spin-polarized saddle points in the topological surface states of elemental bismuth revealed by pump-probe spin- and angle-resolved photoemission spectroscopy

Yuto Fukushima; Kaishu Kawaguchi; Kenta Kuroda; Masayuki Ochi; Motoaki Hirayama; Ryo Mori; Hiroaki Tanaka; Ayumi Harasawa; Takushi Iimori; Zhigang Zhao; Shuntaro Tani; Koichiro Yaji; Shik Shin; Fumio Komori; Yohei Kobayashi; Takeshi Kondo

doi:10.1103/PhysRevB.110.L041401

Letter

Spin-polarized saddle points in the topological surface states of elemental bismuth revealed by pump-probe spin- and angle-resolved photoemission spectroscopy

Yuto Fukushima¹, Kaishu Kawaguchi¹, Kenta Kuroda ^2,3,4, Masayuki Ochi ^5,6, Motoaki Hirayama^7,8, Ryo Mori ¹, Hiroaki Tanaka ¹, Ayumi Harasawa ¹, Takushi Iimori¹ et al.

Zhigang Zhao^1,9, Shuntaro Tani ¹, Koichiro Yaji ¹⁰, Shik Shin¹¹, Fumio Komori ¹, Yohei Kobayashi ¹, and Takeshi Kondo ^1,12,*

¹Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
²Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-hiroshima, Hiroshima 739-8526, Japan
³International Institute for Sustainability with Knotted Chiral Meta Matter (WPI-SKCM²), Hiroshima University, Higashi-hiroshima, Hiroshima 739-8526, Japan
⁴Research Institute for Semiconductor Engineering, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8527, Japan
⁵Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
⁶Forefront Research Center, Osaka University, Toyonaka, Osaka 560-0043, Japan
⁷Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
⁸RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
⁹School of Information Science and Engineering, Shandong University, Qingdao, 266237, China
¹⁰Center for Basic Research on Materials, National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0003, Japan
¹¹Office of University Professor, The University of Tokyo, Kashiwa, Chiba 277-8581 Japan
¹²Trans-scale Quantum Science Institute, The University of Tokyo, Tokyo 113-0033, Japan

^*Contact author: kondo1215@issp.u-tokyo.ac.jp

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Phys. Rev. B 110, L041401 – Published 1 July, 2024

DOI: https://doi.org/10.1103/PhysRevB.110.L041401

Abstract

We use pump-probe, spin- and angle-resolved photoemission spectroscopy (ARPES) with a 10.7 eV laser accessible up to the Brillouin zone edge, and reveal the entire band structure around the Fermi level, including the unoccupied side, for the elemental bismuth (Bi) with the spin-polarized surface states. Our data identify Bi as in a strong topological insulator phase ( $Z_{2} = 1)$ against the prediction of most band calculations. We unveil that the unoccupied topological surface states possess spin-polarized saddle points yielding the van Hove singularity. The unique feature provides an excellent platform for the future development of optospintronics.

Physical Review B

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Spin-polarized saddle points in the topological surface states of elemental bismuth revealed by pump-probe spin- and angle-resolved photoemission spectroscopy

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Spin-polarized saddle points in the topological surface states of elemental bismuth revealed by pump-probe spin- and angle-resolved photoemission spectroscopy

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