Field Electron Emission Spectroscopy of YBa₂Cu₃O_6.9 Single Crystals Above and Below Superconducting Transition Temperature

Abstract
An experimental investigation has been made of the total energy distribution of electrons emitted from the surfaces, purified by field evaporation, of YBa₂Cu₃O_6.9 single crystals oriented in the [100] direction at temperatures above and below superconducting transition temperature. 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 temperature 75 K has the width 30 ± 5 meV.