High-Resolution Photoemission Study of the Low-Energy Excitations Reflecting the Superconducting State of Bi-Sr-Ca-Cu-O Single Crystals

uv-photoemission spectra (hν=21.2 eV) of single-crystal specimens of the high-Tc superconductor Bi₂{Sr}₂$Ca${Cu}₂O₈ have been measured with a resolution of 20 meV in the normal state at 105 K and in the superconducting state at 15 K. In a narrow energy range of 120 meV below the Fermi energy, the low-temperature spectra reveal unambiguously the low-lying quasiparticle excitations reflecting the superconducting state. A straightforward analysis of these spectra provides strong evidence for the existence of a superconducting gap with a reduced value 2ΔkBTc8.