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Diamagnetic activity above Tc as a precursor to superconductivity in La2-xSrxCuO4 thin films

Nature volume 412, pages 420–423 (2001)Cite this article

Abstract

Superconductors show zero resistance to electric current, and expel magnetic flux (the Meissner effect) below the transition temperature (Tc). In conventional superconductors, the ‘Cooper pairs’ of electrons that are responsible for superconductivity form only below Tc. In the unconventional high-Tc superconductors, however, a strong electron correlation is essential for pair formation: there is evidence1,2,3,4,5 that some pairs are formed above Tc in samples that have less than the optimal density of charge carriers (underdoped) and an energy gap—the ‘pseudogap’—appears to be present. Moreover, excitations that look like the vortices that carry magnetic flux inside the superconducting state have been reported above Tc (refs 6, 7). Although the origin of the pseudogap remains controversial8,9,10,11, phase fluctuations above Tc, leading to some form of local superconductivity or local pairing, seem essential9,12,13,14,15,16. Here we report magnetic imaging (scanning SQUID microscopy) of La2-xSrxCuO4 thin films. Clear quantized vortex patterns are visible below Tc (18–19 K), and we observe inhomogeneous magnetic domains that persist up to 80 K. We interpret the data as suggesting the existence of diamagnetic regions that are precursors to the Meissner state.

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Figure 1: Scanning SQUID microscope image of quantized vortices below Tc.
Figure 2: Scanning SQUID microscope image of magnetic domains at 25.5 K above Tc.
Figure 3: Development of magnetic domains with temperature (a–h), as observed by scanning SQUID microscopy.
Figure 4: Development of quantitative scales in the magnetic domains with temperature.

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Acknowledgements

We thank M. Ueda and M. Koyanagi for discussions, and I. Tanaka for providing LSCO single crystals. This work was supported by the CREST program (Core Research for Evolutional Science and Technology) of the Japan Science and Technology Corporation (JST).

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  1. Department of Physics and CREST-JST, Tokyo Institute of Technology, 2-12-1 Oh-okayama, Meguro-ku, 152-8551, Tokyo, Japan

    Ienari Iguchi, Tetsuji Yamaguchi & Akira Sugimoto

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  1. Ienari Iguchi
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Correspondence to Ienari Iguchi.

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Iguchi, I., Yamaguchi, T. & Sugimoto, A. Diamagnetic activity above Tc as a precursor to superconductivity in La2-xSrxCuO4 thin films. Nature 412, 420–423 (2001). https://doi.org/10.1038/35086540

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