Effects of doping on Eu1.5Ce0.5RuSr2Cu2O10: an STM study

Scanning tunneling spectroscopy (STS) is used to study changes in the spati al distribution of the density of states in high-temperature superconductor s as a function of oxygen and hydrogen doping. The STS data correlate well with macroscopic transport measurements. Upon oxygen doping, STS exhibits a n overall increase in the superconducting gap, in agreement with the raisin g of T-C. Small hydrogen doping lowers T-C until the samples become insulat ing at high concentrations. At the same time, STS images show a development of insulating regions which coalesce as the doping is increased. This sugg ests that the superconductor to insulator transition takes place in a perco lative fashion, even though the samples are nominally single phase. (C) 200 0 Elsevier Science B.V. All rights reserved.