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Published Online November 16, 2006
Science DOI: 10.1126/science.1133411

Reports

Submitted on August 3, 2006
Accepted on November 5, 2006

Distinct Fermi-Momentum-Dependent Energy Gaps in Deeply Underdoped Bi2212

Kiyohisa Tanaka 1, W. S. Lee 2, D. H. Lu 2, A. Fujimori 3, T. Fujii 4, * Risdiana 5, I. Terasaki 5, D. J. Scalapino 6, T. P. Devereaux 7, Z. Hussain 8, Z.-X. Shen 2*

1 Department of Physics, Applied Physics, and Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94305, USA; Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, CA 94720, USA.
2 Department of Physics, Applied Physics, and Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94305, USA.
3 Department of Physics and Department of Complexity Science and Engineering, University of Tokyo, Kashiwa, Chiba 277-8561, Japan.
4 Cryogenic Center, University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan.
5 Department of Applied Physics, Waseda University, Tokyo 169-8555, Japan.
6 Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA.
7 Department of Physics, University of Waterloo, Ontario N2L3G1, Canada; Pacific Institute for Theoretical Physics, University of British Columbia, Vancouver, British Columbia, V6T 1Z1, Canada.
8 Advanced Light Source, Lawrence Berkeley National Lab, Berkeley, CA 94720, USA.

* To whom correspondence should be addressed.
Z.-X. Shen , E-mail: zxshen{at}stanford.edu

We use angle-resolved photoemission spectroscopy applied to deeply underdoped cuprate superconductors Bi2Sr2(Ca,Y)Cu2O8 (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, increases 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, does not increase with less doping - a behavior not observed in the single particle spectra before. 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-Tc superconductivity.


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Science. ISSN 0036-8075 (print), 1095-9203 (online)