Local measurement of the superfluid density in the pnictide superconductors $Ba(Fe_{1-x} Co_x )_2 As_2 $ across the superconducting dome

ORAL

Abstract

We locally measure the superfluid density $\rho _s (T)$ in $Ba(Fe_{1-x} Co_x)_2 As_2 $ single crystals with magnetic force microscopy and scanning SQUID susceptometry. These high-precision, local-probe-based techniques enable us to measure both the zero temperature value of the superfluid density $\rho _s (0)$ and the temperature variation, to distinguish homogeneous from spatially varying responses, and to report systematic behavior as a function of Co doping across the superconducting dome. We find that $\rho _s (T)$ increases sharply with decreasing temperature below the superconducting transition temperature $T_c $ of both optimally doped and underdoped compounds, and that $\rho _s (0)$ falls more quickly with $T_c $ on the underdoped side of the dome than on the overdoped. These observations, as well as the increasing temperature induced change of $\rho _s (T)$ at low temperatures upon underdoping, are consistent with magnetic fluctuation mediated pairing and the coexistence of magnetism and superconductivity.

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Authors

  • Lan Luan

    • Stanford institute for materials and energy science, SLAC

  • Thomas Lippman

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

  • C.W. Hicks

    • School of Physics and Astronomy, University of St Andrews

  • Ophir Auslaender

    • Physics Department, Technion-Israel Institute of Technology
    • Technion - Israel Institute of Technology

  • J.A. Bert

    • Stanford University
    • Stanford institute for materials and energy science, SLAC

  • J.-H. Chu

    • Stanford institute for materials and energy science, SLAC
    • SLAC, Stanford University
    • Standford

  • James Analytis

    • Stanford University
    • Stanford institute for materials and energy science, SLAC
    • SLAC, Stanford University
    • SLAC

  • Ian Fisher

    • Department of Applied Physics, Stanford University
    • Stanford University
    • Stanford institute for materials and energy science, SLAC
    • SLAC, Stanford University
    • Stanford

  • Kathryn Moler

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