Measurement of an Anisotropic Energy Gap in Single Plane Bi2Sr2−xLaxCuO6+δ

Abstract

We report angle-resolved photoemission spectra both above and below $T_c$ in the single-plane cuprate superconductor ${\mathrm{Bi}}_2{\mathrm{Sr}}_{2-x}{\mathrm{La}}_x{\mathrm{CuO}}_{6+\delta }$. The superconducting state measurements show a highly anisotropic excitation gap with a maximum magnitude smaller than that of the bilayer compound ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_8$ 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.