Scanning tunneling spectroscopy (STS) is used to study changes in the spatial distribution of the density of states in high-temperature superconductors as a function of oxygen and hydrogen doping. The STS data correlate well with macroscopic transport measurements. Upon oxygen doping, STS exhibits an overall increase in the superconducting gap, in agreement with the raising of Tc. Small hydrogen doping lowers Tc until the samples become insulating at high concentrations. At the same time, STS images show a development of insulating regions which coalesce as the doping is increased. This suggests that the superconductor to insulator transition takes place in a percolative fashion, even though the samples are nominally single phase.
- Density of states
- Spatial distribution