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Spontaneously broken time-reversal symmetry in high-temperature superconductors

Nature Physics volume 11, pages 755–760 (2015)Cite this article

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Abstract

Conventional superconductors are strong diamagnets that, through the Meissner effect, expel magnetic fields. It would therefore be surprising if a superconducting ground state would support spontaneous magnetics fields. Such time-reversal symmetry-broken states have been proposed for the high-temperature superconductors, but their identification remains experimentally controversial. Here we show a route to a low-temperature superconducting state with broken time-reversal symmetry that may accommodate currently conflicting experiments. This state is characterized by an unusual vortex pattern in the form of a necklace of fractional vortices around the perimeter of the material, where neighbouring vortices have opposite current circulation. This vortex pattern is a result of a spectral rearrangement of current-carrying states near the edges.

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Figure 1: Phase diagram of small d-wave superconductor grains.
Figure 2: Temperature-dependent density of states.
Figure 3: Local spectral-current densities.
Figure 4: Edge currents and spontaneous magnetic-field profile.
Figure 5: Tunnelling density of states and magnetic-field distribution.

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Acknowledgements

We thank the Swedish Research Council (VR) via the Linnaeus Center on Engineered Quantum Systems and projects 621-2011-4299 and 621-2012-4597, as well as the Knut and Alice Wallenberg Foundation for financial support. The authors thank A. Vorontsov, J. Sauls, T. Bauch and F. Lombardi for valuable discussions.

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Authors and Affiliations

  1. Department of Microtechnology and Nanoscience—MC2, Chalmers University of Technology, SE-412 96 Göteborg, Sweden

    Mikael Håkansson, Tomas Löfwander & Mikael Fogelström

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  1. Mikael Håkansson
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  2. Tomas Löfwander
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  3. Mikael Fogelström
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Contributions

M.H. prepared and performed the numerical computations and produced all the figures. T.L. and M.F. wrote the paper and supervised the project. All authors planned, analysed and discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Tomas Löfwander or Mikael Fogelström.

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Håkansson, M., Löfwander, T. & Fogelström, M. Spontaneously broken time-reversal symmetry in high-temperature superconductors. Nature Phys 11, 755–760 (2015). https://doi.org/10.1038/nphys3383

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