SUPERCONDUCTING GAP AND ELECTRON-PHONON INTERACTION IN MgB_2 THIN FILM STUDIED BY POINT CONTACTS

摘要

Our results on MgB_2 c-axis oriented thin film investigated by point contacts unequivocally indicate the presence of two SC gaps Δ_(small) ≈ 2.6meV and Δ_(Large) ≈ 7.4 with the theoretically predicted ratio 1:3. Above the SC gap the EPI features are resolved in the PC spectra. Thus the electron-phonon coupling in MgB_2 must therefore be included in any microscopic theory of superconductivity. The reconstructed PC EPI function presumably along c-axis has similarities with the phonon DOS above 30 meV, while additionally resolved maxima at 20 and 30 meV point out that these low frequency phonon modes should be considered by describing of the SC state of MgB_2. Using the barrier-less junction, the Fermi velocity 5x10~7 cm/s in MgB_2 has been estimated.