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

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 (3 root 3 x 3 root 3)R30 degrees 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 Delta(NiPb) approximate to 1.0 meV, in stark contrast to the isotropic Delta(Pb) approximate to 1.3 meV. In addition, the higher density of states at the Fermi energy (D(E-F)) of the Ni-Pb surface alloy results in an enhancement of coherence peak height. According to the same T-c approximate to 7.1 K with Pb(111) from the temperature-dependent Delta(NiPb) and the short decay length L-d approximate to 3.55 nm from the spatially monotonic decrease of Delta(NiPb), 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.