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 su perconducting 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 persis ts well above T-c, behavior previously associated with underdoped bila yer cuprates. The anisotropy and magnitude of the normal-state gap are very similar to the superconducting state gap, indicating that the tw o gaps may have a common origin in a pairing interaction.