Spatial Variations in the Superconductivity ofNb3Sn Measured by Low-Temperature Tunneling Microscopy

The low-temperature scanning tunneling microscope is used in a new spectroscopic mode to obtain real-space images of the superconducting character of a ${\mathrm{Nb}}_3$Sn surface. These images show strong spatial variations, with reproducible transitions between fully normal and fully superconducting behavior on length scales as small as 13 nm. Images taken above and below the critical temperature confirm that the observed effects are due to superconductive tunneling. Additional confirmation comes from a successful fit of the current-voltage characteristics to a simple tunneling model.