Superconducting gap and electron-phonon interaction in MgB$_2$ thin film studied by point contacts

Abstract

The superconducting order parameter and electron-phonon interaction (EPI) in a MgB$_{2}$ c-axis oriented thin film are investigated by point contacts (PCs). Two superconducting gaps $Δ_{Small}\approx 2.6$ meV and $Δ_{Large}\approx 7.4$ meV have been established, which fairly well correspond to the theoretical gap ratio 1:3. The reconstructed PC EPI function along c-axis has above 30 meV similarities with the phonon DOS, while a pronounced maximum around 20 meV is resolved pointing out that the low frequency phonon mode can be of importance for pairing. We have estimated the Fermi velocity in MgB$_2$ about 5$\times 10^7$ cm/s.