Effect of Pt doping on the critical temperature and the upper critical field in YNi_2-xPt_xB₂C for doping range 0< x< 0.2

Abstract

We investigate the evolution of superconducting properties by doping nonmagnetic impurity in single crystals of YNi_2-xPt_xB₂C (x=0–0.2). With increasing Pt doping the critical temperature (T_c) monotonically decreases from 15.85 K and saturates to a value of ∼13 K for x≥0.14. However, unlike usual s-wave superconductors, the upper critical field (H_c2) along both crystallographic directions a and c decreases with increasing Pt doping. Specific-heat measurements show that the density of states [N(E_F)] at the Fermi level (E_F) and the Debye temperatures (Θ_D) in this series remain constant within the error bars of our measurement. We explain our results based on the increase in interband scattering in the multiband superconductor YNi₂B₂C.