Point-contact study of the LuNi2B2C borocarbide superconducting film

Abstract

We present point-contact (PC) Andreev-reflection measurements of a superconducting epitaxialc-axis oriented nickelborocarbide 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 theLuNi2B2C–Cu PC obtained by the two-gap approach provides evidence for multiband superconductivity inLuNi2B2C. For the first time, PC electron–phonon interaction (EPI) spectra have beenmeasured for this compound. They demonstrate a pronounced phonon maximum at8.5 ± 0.4 meV and a secondshallow one at 15.8 ± 0.6 meV. The electron–phonon coupling constantλ estimated from the PC EPI spectra turned out to be small (withλPC ∼ 0.1), like in other superconducting rare-earth nickel borocarbides. Possible reasons for this arediscussed.