Fluctuation conductivity and upper critical field of Y1−xRExNi2B2C (RE=Er, Ho, Dy, Gd) superconductors Original Research Article

We have investigated the upper critical fields of Y1−xRExNi2B2C (RE=Er, Ho, Dy, Gd; 0≤x<1) compounds by using the scaling analysis of the thermal fluctuation conductivity. The thermal fluctuation conductivity can be scaled by a universal function both above and below the mean-field transition temperature for all magnetic fields. A positive curvature is present in Hc2(T). The upward curvature of the Hc2(T) curve in the Y1−xRExNi2B2C system might suggest an intrinsic anomalous pairing mechanism. Based on the value of upper critical field near Tc, the superconducting coherence length is estimated at 6.4 nm for an x=0 sample. The Ginzburg–Landau parameter κ estimated is ∼11 in the pristine YNi2B2C system.