Point-contact study of the LuNi2B2C borocarbide superconducting film

TL;DR

This study uses point-contact Andreev-reflection measurements to investigate the superconducting properties and electron-phonon interactions in LuNi2B2C films, revealing multiband superconductivity and phonon features.

Contribution

First measurement of PC electron-phonon interaction spectra in LuNi2B2C, providing evidence for multiband superconductivity and characterizing phonon modes.

Findings

Superconducting gap values suggest multiband superconductivity.

Electron-phonon coupling constant is small (~0.1).

Pronounced phonon maximum at 8.5 meV and a shallow one at 15.8 meV.

Abstract

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 2.6 +/-0.2 meV in the one-gap approach, whereas the two-gap approach results in 2.14+/-0.36 meV and 3.0+/-0.27 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 pronounced phonon maximum at 8.5+/-0.4meV and a second shallow one at 15.8+/-0.6 meV. The electron-phonon coupling constant estimated from the PC EPI spectra turned out to be small (~ 0.1), like in other superconducting rare-earth nickel borocarbides. Possible reasons for this are discussed.