Local and Global Superconductivity in Bismuth

TL;DR

This study investigates both local and global superconductivity in bismuth, revealing localized superconductivity in powdered samples and induced global superconductivity in polycrystalline samples due to metal contacts, highlighting interface effects.

Contribution

It provides new evidence of superconductivity in bismuth at different scales and clarifies the role of interfaces and contacts in inducing global superconductivity.

Findings

Local superconductivity at ~8.75 K in powdered Bi

Global superconductivity at ~7.3 K in polycrystalline Bi with metal contacts

Superconductivity likely localized at interfaces or grain boundaries

Abstract

We performed magnetization M(H,T) and magnetoresistance R(T,H) measurements on powdered (grain size ~ 149 micrometers) as well as highly oriented rhombohedral (A7) bismuth (Bi) samples consisting of single crystalline blocks of size ~ 1x1 mm2 in the plane perpendicular to the trigonal c-axis. The obtained results revealed the occurrence of (1) local superconductivity in powdered samples with Tc(0) = 8.75 \pm 0.05 K, and (2) global superconductivity at Tc(0) = 7.3 \pm 0.1 K in polycrystalline Bi triggered by low-resistance Ohmic contacts with silver (Ag) normal metal. The results provide evidence that the superconductivity in Bi is localized in a tiny volume fraction, probably at intergrain or Ag/Bi interfaces. On the other hand, the occurrence of global superconductivity observed for polycrystalline Bi can be accounted for by enhancement of the superconducting order parameter phase stiffness induced by the normal metal contacts, the scenario proposed in the context of "pseudogap regime" in cuprates [E. Berg et al., PRB 78, 094509 (2008)].