Experimental evidence of anomalously large superconducting gap on topological surface state of β-Bi2Pd film

Jian-Yu Guan; Lingyuan Kong; Li-Qin Zhou; Yi-Gui Zhong; Hang Li; Hai-Jiang Liu; Cen-Yao Tang; Da-Yu Yan; Fa-Zhi Yang; Yao-Bo Huang; You-Guo Shi; Tian Qian; Hong-Ming Weng; Yu-Jie Sun; Hong Ding

doi:10.1016/j.scib.2019.07.019

Experimental evidence of anomalously large superconducting gap on topological surface state of β-Bi₂Pd film

Sci Bull (Beijing). 2019 Sep 15;64(17):1215-1221. doi: 10.1016/j.scib.2019.07.019. Epub 2019 Jul 19.

Authors

Jian-Yu Guan¹, Lingyuan Kong¹, Li-Qin Zhou¹, Yi-Gui Zhong¹, Hang Li¹, Hai-Jiang Liu¹, Cen-Yao Tang¹, Da-Yu Yan¹, Fa-Zhi Yang¹, Yao-Bo Huang², You-Guo Shi³, Tian Qian⁴, Hong-Ming Weng³, Yu-Jie Sun⁵, Hong Ding⁶

Affiliations

¹ Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; School of Physics, University of Chinese Academy of Sciences, Beijing 100190, China.
² Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China.
³ Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; Songshan Lake Materials Laboratory, Dongguan 523808, China.
⁴ Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China; Songshan Lake Materials Laboratory, Dongguan 523808, China.
⁵ Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China; Songshan Lake Materials Laboratory, Dongguan 523808, China. Electronic address: yjsun@iphy.ac.cn.
⁶ Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China; Songshan Lake Materials Laboratory, Dongguan 523808, China. Electronic address: dingh@iphy.ac.cn.

PMID: 36659601
DOI: 10.1016/j.scib.2019.07.019

Abstract

Connate topological superconductor (TSC) combines topological surface states with nodeless superconductivity in a single material, achieving effective p-wave pairing without interface complication. By combining angle-resolved photoemission spectroscopy and in-situ molecular beam epitaxy, we studied the momentum-resolved superconductivity in β-Bi₂Pd film. We found that the superconducting gap of topological surface state (Δ_TSS ∼ 3.8 meV) is anomalously enhanced from its bulk value (Δ_b ∼ 0.8 meV). The ratio of 2Δ_TSS/k_BT_c ∼ 16.3, is substantially larger than the BCS value. By measuring β-Bi₂Pd bulk single crystal as a comparison, we clearly observed the upward-shift of chemical potential in the film. In addition, a concomitant increasing of surface weight on the topological surface state was revealed by our first principle calculation, suggesting that the Dirac-fermion-mediated parity mixing may cause this anomalous superconducting enhancement. Our results establish β-Bi₂Pd film as a unique case of connate TSCs with a highly enhanced topological superconducting gap, which may stabilize Majorana zero modes at a higher temperature.

Keywords: Multiband superconductivity; Photoemission spectroscopy; Thin film; Topological surface state.