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