Vortex Imaging in Ba(Fe$_{0.93}$Co$_{0.07}$)$_{2}$As$_{2}$ using Small Angle Neutron Scattering

ORAL

Abstract

We report extended studies of the field dependence of the vortex configuration in superconducting Ba(Fe$_{0.93}$Co$_{0.07})_{2}$As$_{2}$ at $T \sim $ 0.1$T_{c}$ ($T_{c}$ = 21 K) using Small Angle Neutron Scattering (SANS). SANS measurements show a ring of scattering indicating a highly disordered vortex lattice mainly due to strong pinning in this material and a very broad rocking curve width. At lower applied fields ($<$ 1 T) the measured scattering vectors ($q)$ are close to the value expected for a hexagonal vortex lattice (VL) [M.R. Eskildsen \textit{et al.}, Phys. Rev. B 79, 100501(R) (2009)] but with increasing fields it falls between $q_{hex}$ and $q_{square}$. A deviation from the hexagonal VL can be related to a Fermi-surface or gap anisotropy in the basal plane. Moreover an exponential fit to the scattered intensity as a function of field for H $>$ 1 T yields a significantly smaller slope than what was found for smaller fields. This work was supported by NSF grants DMR-0804887, PHY-0552843 and DMR-0454672, and DOE BES contract No. DE-AC02-07CH11358.

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Authors

  • P. Das

    University of Notre Dame, IN, USA

  • T.R. O&#039;Brien

    University of Notre Dame, IN, USA

  • M.R. Eskildsen

    University of Notre Dame, IN, USA

  • M. Laver

    NIST Center for Neutron Research, MD, USA, PSI

  • C.D. Dewhurst

    Institut Laue-Langevin, France, Institut Laue Langevin, France

  • N. Ni

    Ames Laboratory and Iowa State University, IA, USA, Ames Laboratory / Iowa State University, Ames Laboratory, Dept of Physics/Ames Laboratory, Iowa State University, Department of Physics and Astronomy, Iowa State University

  • Andreas Kreyssig

    Ames Laboratory and Iowa State University, IA, USA, Ames Laboratory / Iowa State University

  • S.L. Bud&#039;ko

    Ames Laboratory and Iowa State University, IA, USA, Ames Laboratory / Iowa State University, Ames Laboratory, Ames Laboratory/Iowa State University, Dept of Physics/Ames Laboratory, Iowa State University, Ames Laboratory and Department of Physics and Astronomy, Iowa State University

  • P.C. Canfield

    Ames Laboratory and Iowa State University, IA, USA, Ames Laboratory / Iowa State University, Ames Laboratory, Dept of Physics/Ames Laboratory, Iowa State University, Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames Laboratory/Iowa State University

  • Alan Goldman

    Ames Laboratory and Iowa State University, IA, USA, Ames Laboratory / Iowa State University