Point-contact study of the LuNi2B2C borocarbide superconducting film

We present point-contact (PC) Andreev-reflection measurements of a superconducting epitaxial c-axis oriented nickel borocarbide film LuNi2B2C (Tc = 15.9 K). The averaged value of the superconducting gap is found to be meV in the one-gap approach, whereas the two-gap approach results in meV and meV. The better fit of the Andreev-reflection spectra for the LuNi2B2C–Cu PC obtained by the two-gap approach provides evidence for multiband superconductivity in LuNi2B2C. For the first time, PC electron–phonon interaction (EPI) spectra have been measured for this compound. They demonstrate a pronounced phonon maximum at 8.5 ± 0.4 meV and a second shallow one at 15.8 ± 0.6 meV. The electron–phonon coupling constant λ estimated from the PC EPI spectra turned out to be small (with λPC ~ 0.1), like in other superconducting rare-earth nickel borocarbides. Possible reasons for this are discussed.