Superconducting properties of GdxPb1−xMo6S8 (x = 0.5, 0.7, 0.9) compounds

Abstract

For the first time, the temperature dependences of the electrical resistivity ρ(T) were studied in GdxPb1−xMo6S8 (x = 0.5, 0.7, 0.9) compounds in the temperature range 4–18 K and magnetic fields up to 14 T. It is shown that the superconducting transition temperature values Tc decrease from 14.6 K for a compound with x = 0.5 to 11.8 K for x = 0.9. Experimental dependences Hc2(T) were plotted and it was found that the theoretical dependence Hc2(T) within the microscopic theory of Werthamer-Helfand-Hohenberg poorly describes the experimental data for the Gd0.9Pb0.1Mo6S8 compound. At the same time, the fit of Hc2(T) within the Ginzburg-Landau theory is in good agreement with the experimental results for all the studied samples. An explanation of the dependence Hc2(T) of the studied samples from the gadolinium concentration was proposed. The differential resistance for the Gd0.5Pb0.5Mo6S8–Ag heterocontact with resistance RPC ≈ 2.6 Ω was obtained for 2.6 K using point-contact Andreev reflection spectroscopy. As a result, the superconducting gap for Gd0.5Pb0.5Mo6S8 was estimated for the first time to be Δ ≈ 1.95 meV at 2.6 K. The resulting ratio was 2Δ/kTc ≈ 3.02, which is lower than the Bardeen–Cooper–Schrieffer value of 3.52 for conventional weakly coupled superconductors.