Surface and superconducting properties of cleaved high-temperature superconductors

High-resolution electron-energy-loss spectroscopy is used to characterize the resistivity, vibrations, and electronic structure of YBa2Cu3O7 and Bi2Sr2CaCu2O8 single crystals cleaved in ultrahigh vacuum. Cleaved surfaces show a variety of terminations with different properties. Spectroscopy on superconducting regions reveal energy gaps in the ab plane corresponding to 7.80.3kBTc. The superconducting gap in YBa2Cu3O7 shows a non-BCS temperature dependence and appears to be related to a delocalized excitation near 45 meV that persists well above Tc. © 1990 The American Physical Society.