Local measurement of superfluid density in iron-pnictide superconductors $Ba(Fe_{1-x} Co_x )_2 As_2 $ by magnetic scanning probes

ORAL

Abstract

We use magnetic force microscopy (MFM) to measure the local penetration depth $\lambda $ and its temperature dependence $\Delta \lambda $ in $Ba(Fe_{1-x} Co_x )_2 As_2 $ ($x\approx 0.05$,$T_c =18.5K)$ single crystals, complemented by the use of scanning SQUID susceptometry to measure $\Delta \lambda $ down to 0.4 K. We observe that the superfuid density $\rho _s $ over the full temperature range is well described by a clean two-band fully gapped model. We demonstrate that MFM can measure the important and hard-to-determine absolute value of $\lambda $, as well as obtain its temperature dependence and spatial homogeneity in the same measurement. We find $\lambda _{ab} =325\pm 50$nm, hinting that the superconductivity is not limited by phase fluctuation in this underdoped sample. We observe uniform $\rho _s $ on the submicron scale despite the highly disordered vortex pinning.

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Authors

  • Thomas M. Lippman

    • Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.
    • Stanford University

  • Lan Luan

    • Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.
    • Stanford University

  • Ophir M. Auslaender

    • Stanford University

  • Clifford W. Hicks

    • Stanford University

  • Beena Kalisky

    • Stanford University

  • Jiun-Haw Chu

    • GLAM, Stanford University, Ca 94304
    • Stanford University

  • James Analytis

    • Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.
    • GLAM, Stanford University, Ca 94304
    • Stanford University

  • Ian Fisher

    • Stanford
    • Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.
    • GLAM, Stanford University, Ca 94304
    • Stanford University

  • John R. Kirtley

    • Stanford University

  • Kathryn A. Moler

    • Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.
    • Stanford University