Title: Superconductivity at 9 K in Pb-Bi Alloy

Abstract: In the present work, we report the synthesis of Pb-Bi alloy with enhanced Tc up to 9K, which is higher than that of Pb. The alloy is synthesized via solid state reaction route in vacuum encapsulated quartz tube at 700C in an automated furnace. The synthesized sample is characterized by X-ray Diffraction for its phase purity. Rietveld refinement of XRD reveals that the end product is majority hexagonal Pb7Bi3, with minor rhombohedral Bi. The electronic transport measurement shows metallic behavior with the Debye temperature of 108K and a superconductivity transition temperature (Tc) at below 9K, which is maximum till date for any reported Pb-Bi alloy, Pb or Bi at ambient pressure . It is possible that partial substitution of Bi at the Pb site, modifies the free density of electronic states within BCS model to attain the optimum Tc, which is higher by around 2K from the reported Tc of Pb. The superconductor phase diagram derived from magneto-transport measurements reveals that the synthesized alloy is a conventional superconductor with upper critical field (Hc) of 3.9Tesla, which lies well within the Pauli paramagnetic limit.