Photoemission search for the superconducting energy gap of high-TcYBa2Cu3O7

Abstract

Photoemission data ($h\nu =21.2\mathrm{}$ eV) are reported for the high-$T_c$ superconductor Y${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ above and well below $T_c$ and examined for effects due to the formation of the superconducting energy gap. To guide expectations, simulations are also presented based on a BCS quasiparticle excitation expression broadened by a 30-meV experimental resolution. Comparison of the experimental Fermi-edge spectra with the calculations indicates either that the surface region probed is not superconducting or that the superconductivity is in the extreme gapless limit.