Abstract
A long-standing question in the field of superconductivity is whether pairing of electrons can arise in some cases as a result of magnetic interactions instead of electron–phonon-induced interactions as in the conventional Bardeen–Cooper–Schrieffer theory1. A major challenge to the idea of magnetically mediated superconductivity has been the dramatically different behaviour of the cerium and ytterbium heavy-fermion compounds. The cerium-based systems are often found to be superconducting1,2,3,4,5,6, in keeping with a magnetic pairing scenario, but corresponding ytterbium systems, or hole analogues of the cerium systems, are not. Despite searches over two decades there has been no evidence of heavy-fermion superconductivity in an ytterbium system, casting doubt on our understanding of the electron–hole parallelism between the cerium and the ytterbium compounds. Here we present the first empirical evidence that superconductivity is indeed possible in an ytterbium-based heavy-fermion system. In particular, we observe a superconducting transition at Tc=80 mK in high-purity single crystals of YbAlB4 in the new structural β phase7. We also observe a novel type of non-Fermi-liquid state above Tc that arises without chemical doping, in zero applied magnetic field and at ambient pressure, establishing β-YbAlB4 as a unique system showing quantum criticality without external tuning.
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Change history
11 July 2008
In the version of this article previously published online, the bottom right inset of Fig. 1b, was missing its data. The figure has now been corrected in the HTML and pdf versions, and it will appear correctly in the print version.
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Acknowledgements
We thank M. Ichihara and Y. Kiuchi for their transmission electron microscopy and inductively coupled plasma analyses, and A. Kusmartseva, S. S. Saxena, Y. Matsumoto, T. Tomita, J. Yamaura, Y. Uwatoko, D. Pines, Julia Y. Chan, M. Surtherland, E. O’Farrell, Q. Si, M. Imada and C. Pépin for discussions. This work has been supported in part by Grants-in-Aid for Scientific Research from JSPS, by a Grant-in-Aid for Scientific Research on Priority Areas as well as the 21COE program ‘Diversity and Universality in Physics’ from MEXT of Japan and by the NSF of the United States through DMR-0710492.
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Nakatsuji, S., Kuga, K., Machida, Y. et al. Superconductivity and quantum criticality in the heavy-fermion system β-YbAlB4. Nature Phys 4, 603–607 (2008). https://doi.org/10.1038/nphys1002
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DOI: https://doi.org/10.1038/nphys1002
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