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Freek Massee - Cornell University, USA

Imaging Cooper pair formation in the heavy fermion superconductor CeCoIn5

One of the big unresolved mysteries in condensed matter physics is the mechanism of unconventional - including high temperature - superconductivity : what drives the electrons to form Cooper pairs. A key ingredient to solving this problem is detailed knowledge of the band structure of a particular unconventional superconductor, i.e. the locations in energy and momentum where the electrons reside, and the size of the superconducting gap as a function of momentum, d(k). Using spectroscopic imaging scanning tunneling spectroscopy at 250 mK, we image the formation of Cooper pairing in the heavy fermion superconductor CeCoIn5. We detect the spectroscopic signature of a superconducting gap with four nodes oriented along the (+-1,+-1) p/a directions - as expected for a dx2-y2 superconductor. More significantly, we reveal the k-space structure of d (k) on the Fermi surface of the hybridized heavy-fermion band. Thus we demonstrate d (k) of CeCoIn5 is comparably unconventional to its Cu-based and Fe-based counterparts, supporting the common strong-correlation pairing mechanism hypothesis. We subsequently use this information to try to address the mechanism of superconductivity in this heavy fermion superconductor.