Abstract
The energy gap of superconducting Pb islands grown on Si(111) was probed in situ between 5 and 60 monolayers by low-temperature scanning tunneling spectroscopy. was found to decrease from its bulk value as a function of inverse island thickness. Corresponding values, estimated using bulk gap-to- ratio, are in quantitative agreement with ex situ magnetic susceptibility measurements, however, in strong contrast to previous scanning probe results. Layer-dependent ab initio density functional calculations for freestanding Pb films show that the electron-phonon coupling constant, determining , decreases with diminishing film thickness.
- Received 12 December 2008
DOI:https://doi.org/10.1103/PhysRevLett.102.207002
©2009 American Physical Society