Point-Contact Spectroscopy of the Borocarbide Superconductor YNi2B2C in the Normal and Superconducting State

• Published in: Journal of low temperature physics 2007-05, Vol.147 (3-4), p.335-352
• Main Authors: Bashlakov, D. L., Naidyuk, Yu. G., Yanson, I. K., Behr, G., Drechsler, S. -L., Fuchs, G., Schultz, L., Souptel, D.
• Format: Article
• Language: English
• ISSN: 0022-2291; 1573-7357
• DOI: 10.1007/s10909-007-9327-8

Point-contact (PC) spectroscopy measurements of YNi2B2C single crystals in the normal and superconducting (SC) state (T c {asymptotically equal to} 15.4 K) for the main crystallographic directions are reported. The PC study reveals the electron-phonon interaction (EPI) spectral function with dominant phonon maximum around 12 meV and further weak structures (hump or kink) at higher energy at about 50 meV. No 'soft' modes below 12 meV are resolved in the normal state. The PC EPI spectra are qualitatively similar for the different directions. Contrary, directional study of the SC gap results in Delta{[100] {approximately equal to} 1.5 meV for the a direction and Delta{[001] {approximately equal to} 2.3 meV along the c axis; however the critical temperature T c in PC in all cases is near to that in the bulk sample. The value 2Delta[001]/k B T c {approximately equal to} 3.6 is close to the BCS value of 3.52, and the temperature dependence Delta[001](T) is BCS-like, while the for small gap Delta[100](T) is below BCS behavior at T > T c /2 similarly as in the two-gap superconductor MgB2. It is supposed that the directional variation Delta can be attributed to a multiband nature of the SC state in YNi2B2C.