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Imaging Cooper pairing of heavy fermions in CeCoIn5

Nature Physics volume 9, pages 468–473 (2013)Cite this article

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Abstract

The Cooper pairing mechanism of heavy fermionsuperconductors1,2,3,4, long thought to be due to spin fluctuations5,6,7, has not yet been determined. It is the momentum space (k-space) structure of the superconducting energy gap Δ(k) that encodes specifics of this pairing mechanism. However, because the energy scales are so low, it has not been possible to directly measure Δ(k) for any heavy fermion superconductor. Bogoliubov quasiparticle interference imaging8, a proven technique for measuring the energy gaps of superconductors with high critical temperatures9,10,11, has recently been proposed12 as a new method to measure Δ(k) in heavy fermion superconductors, specifically CeCoIn5 (ref. 13). By implementing this method, we detect a superconducting energy gap whose nodes are oriented along k∥(±1,±1)π/a0 directions14,15,16,17. Moreover, for the first time in any heavy fermion superconductor, we determine the detailed structure of its multiband energy gaps Δi(k). For CeCoIn5, this information includes: the complex band structure and Fermi surface of the hybridized heavy bands, the fact that largest magnitude Δ(k) opens on a high- k band so that the primary gap nodes occur at unforeseen k-space locations, and that the Bogoliubov quasiparticle interference patterns are most consistent with d x 2 − y 2 gap symmetry. Such quantitative knowledge of both the heavy band-structure and superconducting gap-structure will be critical in identifying the microscopic pairing mechanism of heavy fermion superconductivity.

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Figure 1: Anticipated electronic structure of a heavy fermion superconductor.
Figure 2: Imaging superconducting gap map and vortex lattice of CeCoIn5.
Figure 3: Determination of heavy fermion bands and Fermi surfaces at B = 0 in CeCoIn5.
Figure 4: Momentum-space superconducting energy gap Δ(k) of CeCoIn5.

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Acknowledgements

We are particularly grateful to I. Eremin, J. E. Hoffman, D-H. Lee and A. R. Schmidt for advice and discussions. We acknowledge and thank A. Akbari, M. Aprili, M. H. Fischer, M. Hamidian, E-A. Kim, S. A. Kivelson, M. Norman, J. P. Reid, D-H. Lee, D. J. Scalapino and K. Shen for helpful discussions, advice and communications. Supported by US DOE under contract number DEAC02-98CH10886 (J.C.D. and C.P.) and under Award No. DE-FG02-05ER46225 (D.K.M., J.v.D.); by the UK EPSRC under programme grant ‘Topological Protection and Non-equilibrium States in Correlated Electron Systems’ (A.R., A.P.M.); M.P.A. acknowledges support through the ETH Fellowship program; A.P.M. acknowledges support of a Royal Society-Wolfson Award.

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Author notes

  1. M. P. Allan and F. Massee: These authors contributed equally to this work

Authors and Affiliations

  1. CMPMS Department, Brookhaven National Laboratory, Upton, New York 11973, USA

    M. P. Allan, F. Massee, C. Petrovic & J. C. Davis

  2. Department of Physics, LASSP, Cornell University, Ithaca, New York 14853, USA

    M. P. Allan, F. Massee, A. W. Rost & J. C. Davis

  3. School of Physics and Astronomy, University of St Andrews, St Andrews, Fife KY16 9SS, UK

    M. P. Allan, A. W. Rost, A. P. Mackenzie & J. C. Davis

  4. Department of Physics, ETH Zurich, CH-8093 Zurich, Switzerland

    M. P. Allan

  5. Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, USA

    D. K. Morr & J. Van Dyke

  6. Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany

    A. P. Mackenzie

  7. Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York 14853, USA

    J. C. Davis

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Contributions

F.M. and M.P.A. carried out SI-STM experiments plus the data preparation; C.P. synthesized and characterized the samples; D.K.M. and J.v.D. developed the band and gap structure models; J.C.D. supervised the project and wrote the paper with key contributions from F.M., M.P.A., D.K.M. and A.P.M. The manuscript reflects the contributions and ideas of all authors.

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Correspondence to D. K. Morr or J. C. Davis.

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Allan, M., Massee, F., Morr, D. et al. Imaging Cooper pairing of heavy fermions in CeCoIn5. Nature Phys 9, 468–473 (2013). https://doi.org/10.1038/nphys2671

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