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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
Yuto f*ckushima, 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, and Takeshi Kondo
Phys. Rev. B 110, L041401 – Published 1 July 2024
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Abstract
We use pump-probe, spin- and angle-resolved photoemission spectroscopy (ARPES) with a 10.7eV 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 ( 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.
- Received 19 March 2023
- Revised 15 November 2023
- Accepted 3 June 2024
DOI:https://doi.org/10.1103/PhysRevB.110.L041401
©2024 American Physical Society
Physics Subject Headings (PhySH)
- Research Areas
Electronic structureSpin polarization
- Physical Systems
Topological materials
- Techniques
Photoemission
Condensed Matter, Materials & Applied Physics
Authors & Affiliations
Yuto f*ckushima1, Kaishu Kawaguchi1, Kenta Kuroda2,3,4, Masayuki Ochi5,6, Motoaki Hirayama7,8, Ryo Mori1, Hiroaki Tanaka1, Ayumi Harasawa1, Takushi Iimori1, Zhigang Zhao1,9, Shuntaro Tani1, Koichiro Yaji10, Shik Shin11, Fumio Komori1, Yohei Kobayashi1, and Takeshi Kondo1,12,*
- 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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Issue
Vol. 110, Iss. 4 — 15 July 2024
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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 (11) Spin-polarized saddle points in the topological surface states of elemental bismuth revealed by pump-probe spin- and angle-resolved photoemission spectroscopy (11)](https://i0.wp.com/cdn.journals.aps.org/development/journals/images/author-services-placard.png)
Images
Figure 1
(a)Crystal structure of Bi in the (111) orientation. (b)Brillouin zone for bulk and (111) surface. (c)Schematic band structure along the - direction on the Bi(111) surface. Blue and red lines show the surface bands (SS1 and SS2) with in-plane spin polarization in opposite directions. (d)–(g) All possible relationships between surface and bulk bands around corresponding to different bulk topologies. [31].
Figure 2
Band structures of Bi revealed by pump-probe ARPES. (a)Fermi surface map. (b), (c)Band dispersion along - measured without and with pump. (d)Energy contour maps on the unoccupied side from 0.10 to 0.25eV. (e), (f) Band dispersions crossing the saddle point along and [momentum cuts e and f marked in (d)]. (g) Three-dimensionally plotted ARPES intensities along , and energy. (h) Schematic of spin-polarized saddle points with a hexagonal structure. Magenta arrows in (c), (e), (f), and (g) indicate the saddle point.
Figure 3
Spin texture of surface states in Bi revealed by pump-probe spin-ARPES. (a), (b)Spin polarization and spin-polarized band along - , respectively. Red and blue represent up and down spin in the direction for two surface bands (SS1 and SS2). The painted areas in (a)represent errors (see more details in the Supplemental Material [55]). (c)High-resolution map of spin polarization around within the black frame in (b). (d)Spin-resolved EDCs at marked by arrows in (c). Energy positions of surface bands are pointed by red and blue arrows. Black curves are the addition of the up- and down-spin spectra. (e) Surface bands determined from spin-resolved EDCs. Fitting curves to the data (solid and dotted lines) are overlayed.
Figure 4
Bulk bands and their relationship with surface bands. (a)Pump-probe ARPES map around . Here, the original spectra are symmetrized across to remove the matrix element effect. They are also divided by the Fermi-Dirac distribution function at the electron temperature (250K) estimated from the spectral edge broadening due to the pumping. (b)MDCs of (a). Thick black lines represent energies of two surface bands. Intensities of BCB and BVB are each painted green and orange. (c)Bulk bands (color bars) obtained from (b)and surface bands (dashed lines) determined in Fig.3 are superimposed. (d)Schematic band structure and characteristic energies obtained in our experiments.
Figure 5
(a)Comparison of characteristic energies in band structures obtained: bottoms of BCB at and , energy of vHS, and energy gaps at between BCB and BVB () and between SS1 and SS2 (). Bulk topology is also listed. is a parameter of the modified Becke-Johnson potential used in our calculations. (b)First-principles band calculations of semi-infinite layer Bi(111) along - for different values. =1.0 corresponds to the original band, whereas the states with less than 1.0 are assigned as trivial (, and those with larger are as nontrivial (.