FIELD ELECTRON-EMISSION SPECTROSCOPY OF YBA2CU3O6.9 SINGLE-CRYSTALS ABOVE AND BELOW SUPERCONDUCTING TRANSITION-TEMPERATURE

An experimental investigation has been made of the total energy distri bution of electrons emitted from the surfaces, purified by field evapo ration, of YBa2Cu3O6.9 single crystals oriented in the [100] direction at temperatures above and below superconducting transition temperatur e. Field electron emission spectroscopic experiments carried out at 75 K visualized the superconducting energy gap at the Fermi-edge of the spectra. The number of electrons in the energy interval inside the gap decreases to the zero level. The double value of the superconducting energy gap for crystallographic direction [100] measured at temperatur e 75 K has the width 30 +/- 5 meV.