Percolative superconductor-to-insulator transition inEu1.5Ce0.5NbSr2Cu2O10

Abstract

We employed scanning tunneling microscopy and spectroscopy combined with macroscopic resistivity and magnetization measurements in the study of the superconductor-to-insulator transition in ceramic ${\mathrm{Eu}}_{1.5}{\mathrm{Ce}}_{0.5}{\mathrm{NbSr}}_2{\mathrm{Cu}}_2{\mathrm{O}}_{10}.$ This superconductor ${(T}_C=29\mathrm{}$ K) is made insulating by hydrogen doping in a nondestructive way, allowing for a reversible transition. We found that although the samples were nominally homogeneous the resistivity and magnetization data are indicative of a granular system. Tunneling measurements directly show that the effect of hydrogen loading is to induce a random insulator-superconductor phase separation, resulting in a percolative granularlike transition.