Measurement of an Anisotropic Energy Gap in Single Plane Bi_2Sr_(2-x)La_xCuO_(6+d)
Jeffrey M. Harris, P. J. White, Z.-X. Shen, H. Ikeda, R. Yoshizaki, H. Eisaki, S. Uchida, W. D. Si, J. W. Xiong, Z.-X. Zhao, D. S. Dessau
Abstract
We report angle-resolved photoemission spectra both above and below T_c in the single-plane cuprate superconductor Bi_2Sr_{2-x}La_xCuO_{6+d}. The superconducting state measurements show a highly anisotropic excitation gap with a maximum magnitude smaller than that of the bilayer compound Bi_2Sr_2CaCu_2O_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.