Distinct Fermi-momentum dependent energy gaps in deeply underdoped Bi2212.

Our recent angle-resolved photoemission spectroscopy study of deeply underdoped cuprate superconductors Bi2Sr2(Ca,R)Cu2O8 (R = Y or Dy) (Bi2212) suggested the presence of two distinct energy gaps exhibiting different doping dependences [1]. One gap, associated with the antinodal region where no coherent peak is observed, increases with underdoping - a behavior known for more than a decade and considered as the general behavior of the gap in the underdoped regime. The other gap, associated with the near nodal regime where a coherent peak can be observed in energy distribution curves (EDCs), does not increase with less doping - a behavior not seen in the single particle spectra before. The theoretical implications of these findings and temperature dependence of the spectra will be discussed. [1] Science, in press. (http://www.sciencemag.org/cgi/content/abstract/1133411)