Proximity-Effect-Induced Anisotropic Superconductivity in a Monolayer Ni-Pb Binary Alloy

Yen Hui Lin, Chia Hsiu Hsu, Iksu Jang, Chia Ju Chen, Pok Man Chiu, Deng Sung Lin, Chien Te Wu, Feng Chuan Chuang*, Po Yao Chang, Pin Jui Hsu

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


A proximity effect facilitates the penetration of Cooper pairs that permits superconductivity in a normal metal, offering a promising approach to turn heterogeneous materials into superconductors and develop exceptional quantum phenomena. Here, we have systematically investigated proximity-induced anisotropic superconductivity in a monolayer Ni-Pb binary alloy by combining scanning tunneling microscopy/spectroscopy (STM/STS) with theoretical calculations. By means of high-temperature growth, the (33×33)R30o Ni-Pb surface alloy has been fabricated on Pb(111) and the appearance of a domain boundary as well as a structural phase transition can be deduced from a half-unit-cell lattice displacement. Given the high spatial and energy resolution, tunneling conductance (dI/dU) spectra have resolved the reduced but anisotropic superconducting gap ΔNiPb≈ 1.0 meV, in stark contrast to the isotropic ΔPb≈ 1.3 meV. In addition, the higher density of states at the Fermi energy (D(EF)) of the Ni-Pb surface alloy results in an enhancement of coherence peak height. According to the same Tc≈ 7.1 K with Pb(111) from the temperature-dependent ΔNiPband the short decay length Ld≈ 3.55 nm from the spatially monotonic decrease of ΔNiPb, both results are supportive of a proximity-induced superconductivity. Despite a lack of a bulk counterpart, the atomically thick Ni-Pb bimetallic compound opens a pathway to engineer superconducting properties down to the two-dimensional limit, giving rise to the emergence of anisotropic superconductivity via a proximity effect.

Original languageEnglish
Pages (from-to)23990-23997
Number of pages8
JournalACS Applied Materials and Interfaces
Issue number20
StatePublished - 25 May 2022


  • anisotropic superconductivity
  • BCS theory
  • BdG Hamiltonian
  • Cooper pairs
  • monolayer Ni-Pb binary alloy
  • proximity effect
  • scanning tunneling spectroscopy
  • self-consistent Usadel model


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