Local and Global Superconductivity in Bismuth

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)].Comment: 12 pages including 9 figures and 1 table, Special Issue to the 80th birthday anniversary of V. G. Peschansky, Electronic Properties of Conducting System

Spin-Orbit Coupling and Anomalous Angular-Dependent Magnetoresistance in the Quantum Transport Regime of PbS

We measured magnetotransport properties of PbS single crystals which exhibit the quantum linear magnetoresistance (MR) as well as the static skin effect that creates a surface layer of additional conductivity. The Shubnikov-de Haas oscillations in the longitudinal MR signify the peculiar role of spin-orbit coupling. In the angular-dependent MR, sharp peaks are observed when the magnetic field is slightly inclined from the longitudinal configuration, which is totally unexpected for a system with nearly spherical Fermi surface and points to an intricate interplay between the spin-orbit coupling and the conducting surface layer in the quantum transport regime.Comment: 5 pages, 5 figure