title: Distinct Fermi-momentum-dependent energy gaps in deeply underdoped Bi2212.
abstract: We used angle-resolved photoemission spectroscopy applied to deeply underdoped cuprate superconductors Bi2Sr2Ca(1-x)YxCu2O8 (Bi2212) to reveal the presence of two distinct energy gaps exhibiting different doping dependence. One gap, associated with the antinodal region where no coherent peak is observed, increased with underdoping, a behavior known for more than a decade and considered as the general gap behavior in the underdoped regime. The other gap, associated with the near-nodal regime where a coherent peak in the spectrum can be observed, did not increase with less doping, a behavior not previously observed in the single particle spectra. We propose a two-gap scenario in momentum space that is consistent with other experiments and may contain important information on the mechanism of high-transition temperature superconductivity.
authors.affiliation: Department of Physics, Department of Applied Physics, and Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94305, USA.
authors.forename: Kiyohisa
authors.initials: K
authors.lastname: Tanaka
authors.forename: W S
authors.initials: WS
authors.lastname: Lee
authors.forename: D H
authors.initials: DH
authors.lastname: Lu
authors.forename: A
authors.initials: A
authors.lastname: Fujimori
authors.forename: T
authors.initials: T
authors.lastname: Fujii
authors.lastname: Risdiana
authors.forename: I
authors.initials: I
authors.lastname: Terasaki
authors.forename: D J
authors.initials: DJ
authors.lastname: Scalapino
authors.forename: T P
authors.initials: TP
authors.lastname: Devereaux
authors.forename: Z
authors.initials: Z
authors.lastname: Hussain
authors.forename: Z-X
authors.initials: ZX
authors.lastname: Shen