Superconducting Proximity Effect in R7xR7R19.1o Ni Nanoislands on Pb(111)

TL;DR

This study investigates the proximity-induced superconductivity in Ni nanoislands on Pb(111) using STM spectroscopy and DFT calculations, revealing a superconducting gap slightly larger than that of Pb and supporting substrate-induced effects.

Contribution

The paper combines experimental STM/STS with DFT calculations to characterize the superconducting proximity effect in Ni nanoislands with a specific surface structure on Pb(111).

Findings

Superconducting gap in Ni nanoislands is 1.29 meV, slightly larger than Pb.

Proximity effect is supported by identical transition temperature of 7.14 K.

Spatial mapping shows increased gap possibly due to electron-phonon interactions.

Abstract

We have studied the proximity_induced superconductivity in R7xR7R19.1o Ni nanoislands by combing scanning tunnelling microscopy_spectroscopy (STM_STS) with density functional theory (DFT) calculation. Through depositing Ni onto Pb(111) substrate at 80 K, the monolayer Ni nanoislands with the R7xR7R19.1o surface structure have been fabricated, where the termination of Ni atoms at hexagonal close packed (hcp) site is energetically preferred and the electron filling of 3d orbitals from the charge transfer leads to the vanishing magnetic moment of Ni atoms. The topographic R7xR7R19.1o lattice as well as the asymmetric height contrast in atomic unit cell are further corroborated by the STM simulations. With high spatial and energy resolution, tunneling conductance spectra have resolved an isotropic superconducting gap with Delta_Ni_(R7xR7R19.1o)_1.29 meV, which is slightly larger than Delta_Pb_1.25 meV. The temperature dependence of Delta_Ni_(R7xR7R19.1o) supports the substrate_induced superconducting proximity effect according to the same transition temperature Tc_7.14 K with the Pb(111). The line spectroscopy has spatially mapped out the small increase of Delta_Ni_(R7xR7R19.1o), which could be explained by an enhanced electron_phonon interaction under the framework of Bardeen_Cooper_Schrieffer (BCS) theory as a manifestation of the hole doping of Pb(111) from the surface Ni atoms.