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 ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ and ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ 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 7.8±0.3$k_B$ $T_c$. The superconducting gap in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ shows a non-BCS temperature dependence and appears to be related to a delocalized excitation near 45 meV that persists well above $T_c$.