High magnetic field vortex torque magnetometry in SmFeAsO$_{0.8}$F$_{0.2}$ single crystals

ORAL

Abstract

To probe manifestations of multiband superconductivity in oxypnictides, we measured the angular dependence of magnetic torque $\tau(\theta)$ in the mixed state of SmO$_{0.8}$F$_{0.2}$FeAs single crystals as functions of temperature $T$ and high magnetic field $H$ up to 30 T. We show that the effective mass anisotropy parameter $\gamma$ extracted from $\tau(\theta)$, can be greatly overestimated if the strong paramagnetism of Sm or Fe ions is not properly taken into account. The correctly extracted $\gamma$ depends on both $T$ and $H$, saturating at $\gamma \simeq 9$ at lower temperatures. Neither the London penetration depth nor the superfluid density is affected by high fields fields up to the upper critical field. Our results indicate two strongly-coupled superconducting gaps of nearly equal magnitudes.

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Authors

  • Luis Balicas

    • NHMFL
    • Florida State University
    • National High Magnetic Field Laboratory, Florida State University, Tallahassee-FL 32310, USA

  • Alex Gurevich

    • National High Magnetic Field Laboratory, Florida State University, Tallahassee-FL 32310, USA

  • Younjung Jo

    • National High Magnetic Field Laboratory, Florida State University, Tallahassee-FL 32310, USA

  • Jan Jaroszynski

    • National High Magnetic Field Laboratory, Florida State University, Tallahassee-FL 32310, USA

  • David Larbalestier

    • National High Magnetic Field Laboratory, Florida State University, Tallahassee-FL 32310, USA

  • R.H. Liu

    • Hefei National Laboratory for Physical Science a Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui

  • H. Chen

    • Hefei National Laboratory for Physical Science a Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui

  • Xianhui H. Chen

    • Hefei National Laboratory for Physical Science a Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui

  • N.D. Zhigadlo

    • Laboratory for Solid State Physics, ETH Z\"{u}rich, CH-8093 Z\"{u}rich, Switzerland

  • S. Katrych

    • Laboratory for Solid State Physics, ETH Z\"{u}rich, CH-8093 Z\"{u}rich, Switzerland

  • Z. Bukowski

    • Laboratory for Solid State Physics, ETH Z\"{u}rich, CH-8093 Z\"{u}rich, Switzerland

  • J. Karpinski

    • Laboratory for Solid State Physics, ETH Z\"{u}rich, CH-8093 Z\"{u}rich, Switzerland