Electronic spectrum of the high-temperature superconducting state

Improved experimental conditions enabled us to increase the signal-to-noise ratio of the photoemission spectra for the superconducting state of ${\mathrm{Bi}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{SrCu}}_2$ ${\mathrm{O}}_8$, taken with high angular and energy resolution. This also enabled us to reveal a pronounced minimum that separates the two basic features of this spectrum, the narrow quasiparticle excitation peak and the still controversial broad band at lower kinetic energies. The minimum is approximately 3Δ below the Fermi level.