On the Surfacegrived State of Cleaved YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7-δ}$ Single Crystals

Angle-resolved photoemission experiments on the cleaved surface of YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7-δ}$ single crystals revealed an intrinsic surface-derived electronic state around the X and Y point of the Brillouin zone with 0.92 eV binding energy. A surface electronic structure different to the bulk can be of basic importance for the surface superconductivity of this high-T$\text{}_{c}$ cuprate. Here we briefly review recent experimental results and present new hydrogen adsorption experiments, demonstrating the surface character of the 0.92 eV state.