Experimental evidence of anomalously large superconducting gap on topological surface state of $β$-$\rm\mathbf{Bi_2Pd}$ film

J. -Y. Guan; L. -Y. Kong; L. -Q. Zhou; Y. -G. Zhong; H. Li; H. -J. Liu; C. -Y. Tang; D. -Y. Yan; F. -Z. Yang; Y. -B. Huang; Y. -G. Shi; T. Qian; H. -M. Weng; Y. -J. Sun; H. Ding

doi:10.1016/j.scib.2019.07.019

arXiv · 1904.11638

Experimental evidence of anomalously large superconducting gap on topological surface state of $β$-$\rm\mathbf{Bi_2Pd}$ film

J. -Y. Guan·L. -Y. Kong·L. -Q. Zhou·Y. -G. Zhong·H. Li·H. -J. Liu·C. -Y. Tang·D. -Y. Yan·F. -Z. Yang·Y. -B. Huang·Y. -G. Shi·T. Qian·H. -M. Weng·Y. -J. Sun·H. Ding

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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 $β$-$\rm{Bi_2Pd}$ film. We found that the superconducting gap of topological surface state ($Δ_{TSS} \sim$ 3.8 meV) is anomalously enhanced from its bulk value ($Δ_b \sim$ 0.8 meV). The ratio of $2Δ_{TSS}/k_BT_c \sim14.2$, is substantially larger than the BCS value. By measuring $β$-$\rm{Bi_2Pd}$ 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 $β$-$\rm{Bi_2Pd}$ 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.

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J. -Y. Guan, L. -Y. Kong, L. -Q. Zhou, Y. -G. Zhong, H. Li, H. -J. Liu, C. -Y. Tang, D. -Y. Yan, F. -Z. Yang, Y. -B. Huang, Y. -G. Shi, T. Qian, H. -M. Weng, Y. -J. Sun, H. Ding. 2019-04-26. Experimental evidence of anomalously large superconducting gap on topological surface state of $β$-$\rm\mathbf{Bi_2Pd}$ film. https://doi.org/10.1016/j.scib.2019.07.019

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