Imaging Cooper pairing of heavy fermions in CeCoIn5

By M. Allan, F. Massee, D. Morr, J. Dyke, A. Rost, A. Mackenzie, C. Petrovic, J. C. Davis. Nature Physics, 2013

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By pushing scanning tunnelling spectroscopy down to millikelvin temperatures, it is now possible to image a heavy fermion superconductor and measure the superconducting gap symmetry, with gap nodes in unexpected momentum-space locations. 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 dx2−y2 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.

Subfields: Condensed Matter Physics, Electronic, Optical and Magnetic Materials

View Paper: https://www.semanticscholar.org/paper/1443eb9f13944055e30c3aa2bf56db4946885357