Detailed studies indicate a superconducting gap in the high-temperature superconductor Bi(2)Sr(2)CaCu(2)O(8). Photoemission measurements with high energy and angle resolution isolate the behavior of a single band as it crosses the Fermi level in both the normal and superconducting states, giving support to the Fermi liquid picture. The magnitude of the gap is 24 millielectron volts.

The electronic structures of single-crystal and ceramic samples of the electron-doped superconductor Nd2-xCe x Cu04->-with x-0 and 0.15 have been studied using resonant photoemission spectroscopy. Comparing these spectra with previous results for La2-xSr x CuC>4 shows that for both electron and hole doping the Fermi level lies at nearly the same energy, in states that fill in the x x 0 insulator gap. We point out that this would occur if the states at the Fermi level obey a Luttinger-type sum rule, i.e., according to standard theory, if the metallic state is a normal Fermi liquid.