Imaging the impact on cuprate superconductivity of varying the interatomic distances within individual crystal unit cells
- J. A. Slezak†,
- Jinho Lee†,‡,
- M. Wang†,
- K. McElroy§,
- K. Fujita†,¶,
- B. M. Andersen‖,
- P. J. Hirschfeld††,
- H. Eisaki‡‡,
- S. Uchida¶, and
- J. C. Davis†,§§,¶¶
- †Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY 14853;
- ‡School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS, Scotland;
- §Department of Physics, University of Colorado, Boulder, CO 80309;
- ‖Nano-Science Center, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark;
- ††Department of Physics, University of Florida, Gainesville, FL 32611;
- ‡‡National Institute of Advanced Industrial Science and Technology, 1-1-1 Central 2, Umezono, Tsukuba, Ibaraki 305-8568, Japan;
- ¶Department of Physics, University of Tokyo, Tokyo 113-8656, Japan; and
- §§Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, NY 11973
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Edited by Anthony Leggett, University of Illinois at Urbana–Champaign, Urbana, IL, and approved December 21, 2007 (received for review July 30, 2007)
Abstract
Many theoretical models of high-temperature superconductivity focus only on the doping dependence of the CuO2-plane electronic structure. However, such models are manifestly insufficient to explain the strong variations in superconducting critical temperature, T c, among cuprates that have identical hole density but are crystallographically different outside of the CuO2 plane. A key challenge, therefore, has been to identify a predominant out-of-plane influence controlling the superconductivity, with much attention focusing on the distance d A between the apical oxygen and the planar copper atom. Here we report direct determination of how variations in interatomic distances within individual crystalline unit cells affect the superconducting energy-gap maximum Δ of Bi2Sr2CaCu2O8+δ. In this material, quasiperiodic variations of unit cell geometry occur in the form of a bulk crystalline “supermodulation.” Within each supermodulation period, we find ≈9 ± 1% cosinusoidal variation in local Δ that is anticorrelated with the associated d A variations. Furthermore, we show that phenomenological consistency would exist between these effects and the random Δ variations found near dopant atoms if the primary effect of the interstitial dopant atom is to displace the apical oxygen so as to diminish d A or tilt the CuO5 pyramid. Thus, we reveal a strong, nonrandom out-of-plane effect on cuprate superconductivity at atomic scale.
Footnotes
- ¶¶To whom correspondence should be addressed at: 622 Clark Hall, Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY 14853. E-mail: jcdavis{at}ccmr.cornell.edu
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Author contributions: J.A.S., J.L., M.W., K.M., K.F., B.M.A., P.J.H., H.E., S.U., and J.C.D. designed research, performed research, contributed new reagents/analytic tools, analyzed data, and wrote the paper.
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The authors declare no conflict of interest.
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This article is a PNAS Direct Submission.
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See Commentary on page 3173.
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This article contains supporting information online at www.pnas.org/cgi/content/full/0706795105/DC1.
- © 2008 by The National Academy of Sciences of the USA
