The Superconducting gap behavior in the antiferromagnetic Nickel-Borocarbide compounds RNi2B2C (R=Dy, Ho, Er, Tm) studied by point-contacts spectroscopy

An general survey of the superconducting (SC) gap study in the title compounds by point-contact (PC) spectroscopy is presented. The SC gap was determined from dV/dI of PCs employing the well-known theory of conductivity for normal metal-superconductor PCs accounting Andreev reflection. The theory was modified by including pair-breaking effects considering the presence of magnetic rare-earth ions. A possible multiband structure of these compounds was also taken into account. The PC study of the gap in the Er-compound (TN ≊ 6 K Tc ≊ 6.5 K) the SC gap has a BCS-like dependence in the AF state. The SC gap for R = Ho (TN ≊5.2 K < Tc ≊ 8.5 K) exhibits below T* ≊5.6 K a single-band BCS-like dependence vanishing above T*, where a specific magnetic order occurs. The difference in the SC gap behavior in the title compounds is attributed to different AF ordering.