Yin, YiZech, MartinWilliams, Tess L.Wang, W. F.Wu, G.Chen, X. H.Hoffman, Jenny2009-06-012009Yin, Yi, Martin Zech, Tess L. Williams, W. F. Wang, G. Wu, X. H. Chen, and Jennifer E. Hoffman. 2009. Physical Review Letters 102(9): 097002.0031-9007http://nrs.harvard.edu/urn-3:HUL.InstRepos:3009616We present an atomic resolution scanning tunneling spectroscopy study of superconducting BaFe<sub>1.8</sub>Co<sub>0.2</sub>As<sub>2</sub> single crystals in magnetic fields up to 9 T. At zero field, a single gap with coherence peaks at [untranscribable character] = 6:25 meV is observed in the density of states. At 9 and 6 T, we image a disordered vortex lattice, consistent with isotropic, single flux quantum vortices. Vortex locations are uncorrelated with strong-scattering surface impurities, demonstrating bulk pinning. The vortex-induced subgap density of states fits an exponential decay from the vortex center, from which we extract a coherence length [untranscribable character] = 27:6 +/- 2:9 [untranscribable character], corresponding to an upper critical field H<sub>c</sub>2 = 43 T.en-USScanning Tunneling Spectroscopy and Vortex Imaging in the Iron Pnictide Superconductor BaFe1:8Co0:2As210.1103/PhysRevLett.102.097002