Limits on the Superconducting Order Parameter in NdFeAsO$_{1-x}$F$_y$ and SmFeAsO$_{1-x}$ from Scanning SQUID Microscopy

ORAL

Abstract

As a test of the symmetry of the order parameter of the ferric oxyarsenide family of superconductors RFeAsO$_{1-x}$F$_y$, where R is a rare earth, we perform scanning SQUID microscopy on dense polycrystalline samples of NdFeAsO$_{0.94}$F$_{0.06}$ and SmFeAsO$_{0.85}$. Dominant $d$- or $p$-wave orders, for example, would result in direction-dependent phase shifts in tunneling. In well-coupled polycrystalline samples, these phase shifts would result in spontaneous orbital currents and magnetization in the superconducting state. We do not find any spontaneous currents in NdFeAsO$_{0.94}$F$_{0.06}$ or SmFeAsO$_{0.85}$, ruling out order parameters with direction-dependent phase shifts in tunneling.

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Authors

  • Thomas Lippman

    Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, 94305, USA, Geballe Laboratory for Advanced Materials, Stanford University

  • Cliffird Hicks

    Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, 94305, USA, Geballe Laboratory for Advanced Materials, Stanford University

  • Martin Huber

    Department of Physics, University of Colorado Denver, Departments of Physics and Electrical Engineering, University of Colorado Denver, Denver, Colorado, 80217, USA, University of Colorado Denver and NIST

  • Zhi-An Ren

    National Laboratory for Superconductivity, Chinese Academy of Sciences, P.O. Box 603, Beijing 100190, P.R. China

  • Zhong-Xian Zhao

    National Laboratory for Superconductivity, Chinese Academy of Sciences, P.O. Box 603, Beijing 100190, P.R. China

  • Kathryn Moler

    Stanford University, Geballe Laboratory for Advanced Materials, Stanford University, Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, 94305, USA