Upper critical field pecularities of superconducting YNi2B2C and LuNi2B2C

摘要

We present new upper critical field Hc2(T) data in a broad temperature regionfrom 0.3K to Tc for LuNi2B2C and YNi2B2C single crystals with wellcharacterized low impurity scattering rates. The absolute values for all T, inparticular Hc2(0), and the sizeable positive curvature (PC) of Hc2(T) at highand intermediate T are explained quantitatively within an effective two-bandmodel. The failure of the isotropic single band approach is discussed indetail. Supported by de Haas van Alphen data, the superconductivity revealsdirect insight into details of the electronic structure. The observed maximalPC near Tc gives strong evidence for clean limit type II superconductors.