Physical properties of Lu1-xYbxNi2B2C

The Lu1−x Yb x Ni2B2 system exhibits superconductivity at low Yb concentrations (0≤x≤ 0.1), Kondo behaviour at low and moderate Yb concentrations (0≤x≤ 0.34), and heavy fermion behaviour with a non-magnetic ground state at high Yb concentrations. In order to characterize the evolution of these phenomena with x, we have performed dc magnetic susceptibility, electrical resistivity, thermoelectric power, and specific heat measurements on single crystals of Lu1−x Yb x Ni2B2 with various values of x between 0 and 1. The enhanced suppression of T c by Yb substitution, compared to other rare earth substitutions, is consistent with the behaviour of superconducting Kondo systems with T K≫T c when T K decreases with increasing x. The electronic specific heat coefficient γ increases from ∼11 mJ/mol K2 for x=0 to ∼530 mJ/mol K2 for x=1. The curve of the reduced specific heat jump ΔC/ΔC 0 versus T c/T c0, where ΔC 0 and T c0 refer to the LuNi2B2C matrix, does not conform to the BCS theory, but is consistent with the m...