Mode-selected electron-phonon coupling in superconducting Pb nanofilms determined from He atom scattering

The electron-phonon coupling (EPC) strength for each phonon mode in superconducting Pb films is measured by inelastic helium atom scattering (IHAS). This surprising ability of IHAS relies on two facts: (a) In ultrathin metal films, the EPC range exceeds the film thickness, thus enabling IHAS to detect most film phonons, even 1 nm below the surface; (b) IHAS scattering amplitudes from single phonons are shown, by first-principle arguments, to be proportional to the respective EPC strengths. Thus IHAS is the first experiment providing mode-selected EPC strengths (mode-lambda spectroscopy). © 2011 American Physical Society.
One of us (G.B.) acknowledges the Ikerbasque Foundation for support (project ABSIDES). We also acknowledge partial support by the Department of Education of the Basque Country Government, the University of the Basque Country (project GV-UPV/EHU, Grant No. IT-366-07), Ministerio de Ciencia y Innovación (Grant No. FIS2010-19609-C02-00).