Letter | Published:

Scale-free structural organization of oxygen interstitials in La2CuO4+y

Nature volume 466, pages 841844 (12 August 2010) | Download Citation


It is well known that the microstructures of the transition-metal oxides1,2,3, including the high-transition-temperature (high-Tc) copper oxide superconductors4,5,6,7, are complex. This is particularly so when there are oxygen interstitials or vacancies8, which influence the bulk properties. For example, the oxygen interstitials in the spacer layers separating the superconducting CuO2 planes undergo ordering phenomena in Sr2O1+yCuO2 (ref. 9), YBa2Cu3O6+y (ref. 10) and La2CuO4+y (refs 11–15) that induce enhancements in the transition temperatures with no changes in hole concentrations. It is also known that complex systems often have a scale-invariant structural organization16, but hitherto none had been found in high-Tc materials. Here we report that the ordering of oxygen interstitials in the La2O2+y spacer layers of La2CuO4+y high-Tc superconductors is characterized by a fractal distribution up to a maximum limiting size of 400 μm. Intriguingly, these fractal distributions of dopants seem to enhance superconductivity at high temperature.

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We are grateful to the ID13 beamline staff at ESRF, R. Davies, S. Agrestini, V. Palmisano, E. J. Sarria, L. Simonelli and A. Vittorini Orgeas for help in the early stage of this research project. We thank J. Zaanen and G. Bianconi for suggestions, comments and help with the data analysis. This experimental work has been carried out with the financial support of the European STREP project 517039 “Controlling Mesoscopic Phase Separation” (COMEPHS) (2005–2008) and Sapienza University of Rome, research project “Stripes and High-Tc Superconductivity”.

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Author notes

    • Michela Fratini

    Present address: Institute for Photonic and Nanotechnologies, CNR, Via Cineto Romano 42, 00156 Roma, Italy.


  1. Department of Physics, Sapienza University of Rome, Piazzale Aldo Moro 2, 00185 Roma, Italy

    • Michela Fratini
    • , Nicola Poccia
    • , Alessandro Ricci
    • , Gaetano Campi
    •  & Antonio Bianconi
  2. Institute of Crystallography, CNR, Via Salaria Km 29.300, Monterotondo Stazione, Roma, I-00016, Italy

    • Gaetano Campi
  3. European Synchrotron Radiation Facility, B.P. 220, F-38043 Grenoble Cedex, France

    • Manfred Burghammer
  4. London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, 17–19 Gordon Street, London WC1H 0AH, UK

    • Gabriel Aeppli


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A.B. and M.F. designed the experiment; M.B. provided the X-ray beamline; N.P., A.R. and M.F. performed the data analysis. All authors contributed to providing experimental support, interpreting data and writing the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Antonio Bianconi.

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  1. 1.

    Supplementary Information

    This file contains Supplementary Information comprising Micro X-ray diffraction experimental set up; Surface resistivity method; The spatial correlation function and Supplementary Figures 1-2 with legends.

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