Laura H. Greene, National MagLab, Florida State University

3:00 pm GCIS

Room W301

"Local Moment Pairing in the Heavy-Fermion Superconductor CeCoIn_5"

The heavy-fermion superconductor CeCoIn5 has a pairing symmetry of dx2-y2 but the pairing mechanism remains unknown. Our planer tunneling spectroscopy measurements on single crystals into the three major crystallographic orientations as a function of temperature down to 20 mK and fields up to 18 T are reproducible, and our diagnostics show transport across the barrier is predominately single-step elastic tunneling. [1] At low temperatures, on the (100) and (001) faces, we find sharp coherence peaks with an estimated gap of 0.65 meV, and on the (110) face, a broad zero-bias peak. Previously published STM work reports observing pair potentials above Tc = 2.3 K [2]; we also find pre-formed pairs up to Tp ~ 5 K. Below Tp, with increasing applied field, the pairing gap evolves smoothly to a field-induced gap, that grows linearly up to 18 T, the highest field measured. At higher temperatures, no field-induced gap is observed, showing that pairing and the field-induced gap exist concomitantly. Kondo scattering plays a role in the pairing mechanism, and composite pairing remains a possible explanation. [3]
Host: Peter Littlewood, 773-834-4879 or via email at littlewood@uchicago.edu. Persons who may need assistance contact Brenda Thomas at 773-702-7156 or via email at bthomas@uchicago.edu.

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Oct 8