Tunneling measurements of the dependence of the energy gap on critical temperature in La2-xSrxCuO4-y

We have used a low-temperature, in situ cleaving, scanning tunneling microscope to measure the energy gap in a series of La2-xSrxCuO4-y samples with different Sr doping concentrations x, and therefore different critical temperatures. The current-voltage characteristics vary from measurement to measurement, but consistent results can be obtained by selecting "high-quality" data. We discuss the criteria used for this selection. We find that the measured gaps scale with critical temperature with the ratio 2"kBTc1/45. © 1988 The American Physical Society.