Direct Observation of the Surface Superconducting Gap in the Topological Superconductor Candidate <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>β</mi><mtext>−</mtext><msub><mrow><mi>PdBi</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow></math>

Akifumi Mine; Takeshi Suzuki; Yigui Zhong; Sahand Najafzadeh; Kenjiro Okawa; Masato Sakano; Kyoko Ishizaka; Shik Shin; Takao Sasagawa; Kozo Okazaki

doi:10.1103/3jgn-22rx

Direct Observation of the Surface Superconducting Gap in the Topological Superconductor Candidate $β − {PdBi}_{2}$

Akifumi Mine ¹, Takeshi Suzuki ^1,*,†, Yigui Zhong ¹, Sahand Najafzadeh¹, Kenjiro Okawa ^2,‡, Masato Sakano ^3,4,§, Kyoko Ishizaka^3,4,5, Shik Shin^1,6,7, Takao Sasagawa^2,8 et al.

Kozo Okazaki^1,7,9,∥

¹Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
²Materials and Structures Laboratory, Institute of Science Tokyo, Yokohama, Kanagawa 226-8501, Japan
³Department of Applied Physics, The University of Tokyo, Hongo, Tokyo 113-8656, Japan
⁴Quantum-Phase Electronics Center (QPEC), The University of Tokyo, Hongo, Tokyo 113-8656, Japan
⁵RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
⁶Office of University Professor, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
⁷Material Innovation Research Center, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
⁸Research Center for Autonomous Systems Materialogy, Institute of Science Tokyo, Yokohama, Kanagawa 226-8501, Japan
⁹Trans-scale Quantum Science Institute, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan

^*Contact author: suzuki.takeshi.fbs@osaka-u.ac.jp
^†Present address: Graduate School of Frontier Biosciences, The University of Osaka, 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan.
^‡Present address: National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563, Japan.
^§Present address: Graduate School of Informatics and Engineering, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan.
^∥Contact author: okazaki@issp.u-tokyo.ac.jp

PDF

Phys. Rev. Lett. 135, 236002 – Published 1 December, 2025

DOI: https://doi.org/10.1103/3jgn-22rx

Abstract

$β − {PdBi}_{2}$ is one of the candidates for topological superconductors with a superconducting (SC) transition temperature ( $T_{c}$ ) of 5.3 K, in which parity mixing of a spin singlet and spin triplet has been anticipated, being crucial for the further understanding of the relationship with inversion symmetry and parity mixing in the superconductivity. In this Letter, we measured the SC gap in a high-quality single crystal of $β − {PdBi}_{2}$ by using high-resolution laser angle-resolved photoemission spectroscopy below $T_{c}$ . We found the isotropic SC gaps in momentum space for multiple bands, and observed that the difference between the SC gap of the topological surface bands and the bulk bands is about 0.1 meV, consistent with other experimental results. These direct and quantitative experimental results support the possibility of $β − {PdBi}_{2}$ as a topological superconductor, characterized by unique crystal and electronic band structures.

Physical Review Letters

Export citation

Export citation

Direct Observation of the Surface Superconducting Gap in the Topological Superconductor Candidate $β − {PdBi}_{2}$

Abstract

Physics Subject Headings (PhySH)

Authorization Required

Other Options

Supplemental Material (Subscription Required)

References (Subscription Required)

Outline

Information

Filter

Filter

Article Lookup

Enter a citation

Direct Observation of the Surface Superconducting Gap in the Topological Superconductor Candidate β−PdBi2

Abstract

Physics Subject Headings (PhySH)

Authorization Required

Log in via your institution

Log in via APS Member Subscription

Other Options

Supplemental Material (Subscription Required)

References (Subscription Required)

Direct Observation of the Surface Superconducting Gap in the Topological Superconductor Candidate $β − {PdBi}_{2}$