Measurements of the superconducting gap of La-Sr-Cu-O with a scanning-tunneling microscope

Abstract

We report the first tunneling measurements made on the new high-transition-temperature perovskite superconductors. These were obtained using an ultrahigh-vacuum low-temperature scanning-tunneling microscope. The superconducting gap of a ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathrm{y}}$ sample is 12\ifmmode\pm\else\textpm\fi{}3 mV, and the onset ${T}_{c}$ is 40 K, from which 2\ensuremath{\Delta}/${k}_{B}$${T}_{c}$=7\ifmmode\pm\else\textpm\fi{}2. The possibility that this surprisingly high ratio may be due to a mechanism other than superconductivity is discussed.