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Scanning Tunneling Spectroscopy and Vortex Imaging
in the Iron-Pnictide High-Tc Superconductors
Monday, March 9, 2009
12 noon
The Johns Hopkins University
Henry A.
Rowland Department of Physics and Astronomy
Bloomberg Center Room 475
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ABSTRACT: Last year, 22 years after the discovery of high-Tc superconductivity in the cuprates, superconductivity was discovered up to 55K in a second family of materials: the iron-pnictides. This new discovery has generated tremendous excitement for several reasons. First, there is hope that the iron-pnictides will finally provide the foil necessary to understand the enormous yet puzzling body of research on the cuprates. Second, initial reports of low anisotropy and strong vortex pinning in these new materials have spurred optimism that the iron-pnictides may finally lead to the widespread technological applications which have been elusive for cuprates. In this talk, I will summarize the current state of iron-pnictides research, before presenting our own work: the first scanning tunneling spectroscopic imaging study of a single crystal iron-pnictide superconductor in high magnetic fields. We study optimally doped BaFe1.8Co0.2As2 with Tc =25.3K, finding a ~6 meV superconducting gap with nanoscale inhomogeneity, which leads to an average reduced gap of 2Delta/kBTc~5.7. We further observe a static disordered vortex lattice at 9 T, and demonstrate that vortices are pinned in the bulk of this material, a promising observation for practical application.
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