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Visualizing pair formation on the atomic scale in the high-Tc superconductor Bi2Sr2CaCu2O8+δ

Nature volume 447, pages 569–572 (2007)Cite this article

Abstract

Pairing of electrons in conventional superconductors occurs at the superconducting transition temperature Tc, creating an energy gap Δ in the electronic density of states (DOS)1. In the high-Tc superconductors, a partial gap in the DOS exists for a range of temperatures above Tc (ref. 2). A key question is whether the gap in the DOS above Tc is associated with pairing, and what determines the temperature at which incoherent pairs form. Here we report the first spatially resolved measurements of gap formation in a high-Tc superconductor, measured on Bi2Sr2CaCu2O8+δ samples with different Tc values (hole concentration of 0.12 to 0.22) using scanning tunnelling microscopy. Over a wide range of doping from 0.16 to 0.22 we find that pairing gaps nucleate in nanoscale regions above Tc. These regions proliferate as the temperature is lowered, resulting in a spatial distribution of gap sizes in the superconducting state3,4,5. Despite the inhomogeneity, we find that every pairing gap develops locally at a temperature Tp, following the relation 2Δ/kBTp = 7.9 ± 0.5. At very low doping (≤0.14), systematic changes in the DOS indicate the presence of another phenomenon6,7,8,9, which is unrelated and perhaps competes with electron pairing. Our observation of nanometre-sized pairing regions provides the missing microscopic basis for understanding recent reports10,11,12,13 of fluctuating superconducting response above Tc in hole-doped high-Tc copper oxide superconductors.

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Figure 1: Spectroscopy at a specific atomic site as a function of temperature (d I /d V versus sample bias V).
Figure 2: Gap evolution for overdoped ( T c = 65 K) samples.
Figure 3: Gap evolution at different dopings.
Figure 4: Pseudogap and pairing gaps in underdoped samples.
Figure 5: Schematic phase diagram for Bi2Sr2CaCu2O8+δ.

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Acknowledgements

This work was supported by Princeton University, the NSF-DMR, and the NSF-MRSEC programme through the Princeton Center for Complex Materials.

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Author notes

  1. Kenjiro K. Gomes, Abhay N. Pasupathy and Aakash Pushp: These authors contributed equally to this work.

Authors and Affiliations

  1. Department of Physics, Joseph Henry Laboratories, Princeton University, Princeton, New Jersey 08544, USA,

    Kenjiro K. Gomes, Abhay N. Pasupathy, Aakash Pushp & Ali Yazdani

  2. Central Research Institute of Electric Power Industry, Komae, Tokyo 201-8511, Japan,

    Shimpei Ono & Yoichi Ando

Authors
  1. Kenjiro K. Gomes
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  3. Aakash Pushp
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Correspondence to Ali Yazdani.

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This file contains Supplementary Notes, Supplementary Figures S1-S7 with Legends and additional references. (PDF 1278 kb)

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Gomes, K., Pasupathy, A., Pushp, A. et al. Visualizing pair formation on the atomic scale in the high-Tc superconductor Bi2Sr2CaCu2O8+δ. Nature 447, 569–572 (2007). https://doi.org/10.1038/nature05881

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