Superconductivity at 9 K in Pb-Bi Alloy

TL;DR

This study reports the synthesis of a Pb-Bi alloy with a record Tc of 9K, using solid-state methods, and characterizes its structural, electronic, and superconducting properties, revealing it as a conventional, strongly coupled, type-II superconductor.

Contribution

It presents the first Pb-Bi alloy with Tc up to 9K synthesized via a solid-state route, with detailed structural and superconducting property analysis.

Findings

Tc of 9K is the highest for Pb-Bi alloys at ambient pressure.

The alloy is a bulk, strongly coupled, type-II superconductor.

The material exhibits a critical field of 3.9 Tesla.

Abstract

In the present work, we report the synthesis of Pb-Bi alloy with enhanced Tc of up to 9K, which is higher than that of Pb. The alloy is synthesized via a solid-state reaction route in the vacuum-encapsulated quartz tube at 7000C in an automated furnace. The synthesized sample is characterized by X-ray Diffraction(XRD) and Energy dispersive X-ray analysis(EDAX) for its phase purity and elemental composition. Rietveld refinement of XRD reveals that the end product is a 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) below 9K, which is the maximum to date for any reported Pb-Bi alloy, Pb or Bi at ambient pressure. Partial substitution of Bi at the Pb site may modify the free density of electronic states within the 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 an upper critical field (Hc2) of 3.9 Tesla, which lies well within the Pauli paramagnetic limit. The magnetization measurements carried out following ZFC(Zero Field Cool) protocols infer that the synthesized alloy is a bulk superconductor below 9K. The isothermal M-H(Magnetization vs. Field) measurements performed below Tc establish it as a type-II superconductor. The specific heat capacity measurements show that the Pb-Bi alloy is a strongly coupled bulk superconductor below around 9K with possibly two superconducting gaps.