Multiband superconductivity in YNi₂B₂C single crystals studied by use of specific-heat measurements

We present new specific-heat data for two different YNi₂B₂C single crystals grown by a zone-melting method. The two samples (T_c,A = 15.26(4)K, T_c,B = 15.6(1) K) were studied in magnetic fields up to B = 9 T in the temperature range from T = 0.35 . . . 20 K, using both a relaxation and a heat-pulse method. In the superconducting state (B = 0) we find an uncommon dependence of the electronic contribution to the specific heat, C_el(T), strengthening the assumption of a multiband nature of the superconducting state of YNi₂B₂C. A quantitative analysis of C_el(T) evidences multiple electronic contributions from electrons with very different electron-phonon coupling strengths, thus exhibiting several different superconducting energy gaps Δ(T,B = 0). This feature is in agreement with recent de Haas–van Alphen results [1] and point-contact spectroscopy data [2].