Superconducting gap and electron-phonon interaction in MgB₂ thin film studied by point contacts

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The superconducting order parameter and electron-phonon interaction (EPI) in a MgB₂ c-axis oriented thin film are investigated by point contacts (PCs). Two superconducting gaps ΔSmall≈ 2.6 meV and ΔLarge≈ 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 MgB₂ about 5× 10⁷ cm/s.