Superconductivity in Colloidal Pb Nanocrystals
Superconductivity generates perpetual fundamental interest and has promising practical applications; however colloidal nanoparticles of superconducting metals receive little attention from the nanoscale community. In this talk I will describe our efforts to address a problem of building a nanostructured superconductor from the bottom-up perspective. Colloidal Pb nanocrystals with diameters ranging from 4.4 to 20 nm were prepared by a self-limiting growth method.
The nanoparticles are monodispersed and protected from oxidation by an amorphous tin-lead oxide shell of 1.5-2 nm thickness. The magnetic susceptibility of the particles was measured as a function of size, temperature, and magnetic field. The Meissner effect is observed indicating the superconducting transition in the individual particles. The coupling between particles could be controlled through the conversion of the oxides to chalcogenides. This transformation allows for a 109-fold increase in the conductivity. Stepwise conversion allows one to trace the evolution of the film of nanocrystals from insulating to superconducting state. Details of this transition will be discussed.