Berlin 2015 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 98: Focus Session: Visualization of Heavy Fermion Formation through Scanning Tunneling Microscopy

TT 98.5: Hauptvortrag

Donnerstag, 19. März 2015, 17:15–17:45, H 0104

Visualizing the Formation and Magnetically-Mediated Cooper Pairing of Heavy Fermions — •JC Seamus Davis — Cornell University, Ithaca, NY 14850, USA

We recently introduced spectroscopic imaging STM to the study of heavy fermions and achieved the first heavy-quasiparticle interference imaging and direct observation of splitting of a light k-space band into two new heavy fermion bands due to the hybridization process (Nature 465, 570 (2010)). Key specifics of the Cooper pairing mechanism are encrypted in the k-space structure of the superconducting energy gaps Δ_α,β (k) on the heavy bands E(k)_α,β. With energy scales for both these effects so low (sub meV), it was impossible to directly measure Δ (k) for any heavy-fermion superconductor. We introduced Bogoliubov quasiparticle interference (QPI) imaging using milli-Kelvin STM for CeCoIn₅. The heavy band structure E(k)_α,β, the Fermi surface, plus the superconducting Δ_α,β (k) structure were measured directly for the first time (Nature Physics 9, 458 (2013)). Novel SI-STM techniques to measure the k-space structure of the f-electron magnetic interactions were introduced for CeCoIn₅. Solving the superconducting gap equations on the measured E(k)_α,β with the hypothesis that these magnetic interactions mediate the Cooper pairing, reveals succession of quantitative predictions about the superconducting state. We established excellent quantitative agreement between these diverse predictions and many measured characteristics of CeCoIn₅. This provides the first direct evidence that its heavy fermion Cooper pairing is mediated by the f-electron magnetism. (PNAS 111, 11663 (2014))