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Originally published in Science Express on 16 November 2006
Science 22 December 2006:
Vol. 314. no. 5807, pp. 1910 - 1913
DOI: 10.1126/science.1133411
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Reports

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

Kiyohisa Tanaka,1,2 W. S. Lee,1 D. H. Lu,1 A. Fujimori,3 T. Fujii,4 Risdiana,5 I. Terasaki,5 D. J. Scalapino,6 T. P. Devereaux,7,8 Z. Hussain,2 Z.-X. Shen1*

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.

1 Department of Physics, Department of Applied Physics, and Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94305, USA.
2 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, 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.
8 Pacific Institute for Theoretical Physics, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.

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

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Extending Universal Nodal Excitations Optimizes Superconductivity in Bi2Sr2CaCu2O8+{delta}.
A. Pushp, C. V. Parker, A. N. Pasupathy, K. K. Gomes, S. Ono, J. Wen, Z. Xu, G. Gu, and A. Yazdani (2009)
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Energy Gaps and Kohn Anomalies in Elemental Superconductors.
P. Aynajian, T. Keller, L. Boeri, S. M. Shapiro, K. Habicht, and B. Keimer (2008)
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Science. ISSN 0036-8075 (print), 1095-9203 (online)