Measurement of an anisotropic energy gap in single plane Bi2Sr2-xLaxCuO6+delta

We report angle-resolved photoemission spectra both above and below T-c in the single-plane cuprate superconductor Bi2Sr2-xLaxCuO6+8. The superconducting state measurements show a highly anisotropic excitation gap with a maximum magnitude smaller than that of the bilayer compound Bi2Sr2CaCu2O8 by a factor of 3. For a range of doping, the gap persists well above T-c, behavior previously associated with underdoped bilayer cuprates. The anisotropy and magnitude of the normal-state gap are very similar to the superconducting state gap, indicating that the two gaps may have a common origin in a pairing interaction.