Very High Field Two-Band Superconductivity in LaFeAsO_0.89F_0.11

Abstract

The ongoing search for new superconductors has recently yielded a new family of oxypnictides composed of alternating La_2O_{2-x}F_x and Fe_2As_2 layers [1-4] with transition temperatures T_c of 25-28 K, which can be raised to 40-43 K by replacing La with Ce [5] or Sm [6] or to 52 K by replacing La with Nd and Pr [7, 8]. Recent experiments and band structure calculations have suggested an unconventional multiband superconductivity in the layers of paramagnetic Fe ions, which would normally destroy superconductivity in the traditional mechanism of the s-wave Cooper pairing. Here we report very high-field resistance measurements up to 45T, which show a remarkable enhancement of the upper critical fields B_c2 at low temperatures, as compared to those expected from the already high slopes of dB_c2/dT ~ 2T/K near T_c . The deduced B_c2(0) ~ 63-65 T exceeds the paramagnetic limit, consistent with strong coupling and important two-band effects in LaFeAsO_0.89F_0.11. We argue that oxypnictides are emerging as a new class of high-field superconductors surpassing the B_c2 of Nb_3Sn, MgB_2, and the Chevrel phases and perhaps approaching the 100T field benchmark of the high-T_c cuprates.

7 pages, 2 figures, title and abstract include subscripts and special characters

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• Fishtail effect and the vortex phase diagram of single crystal Ba0.6K0.4Fe2As2
• Hall effect and magnetoresistance in the normal state of the superconductor LaO${}_{0.9}$F${}_{0.1-x}$FeAs
• Quantum oscillations in the parent magnetic phase of an iron arsenide high temperature superconductor
• 19-F NMR Investigation of Iron-pnictide Superconductor LaFeAsO(0.89)F(0.11)
• Evidence for two distinct scales of current flow in polycrystalline Sm and Nd iron oxypnictides
• Intrinsic Properties of Stoichiometric LaOFeP
• High pressure synthesis of late rare earth RFeAs(O,F) superconductors; R = Tb and Dy
• Superconducting properties of SmO1-xFxFeAs wires with Tc = 52 K prepared by the powder-in-tube method
• Magnetization Relaxation and Collective Vortex Pinning in the Fe-Based Superconductor SmFeAsO_0.9F_0.1
• Evidence for electromagnetic granularity in the polycrystalline iron-based superconductor LaO0.89F0.11FeAs
• Coexistence of Supercondcutivity and Magnetism in LaFeAs(O0.94F0.06) Probed by Muon Spin Relaxation
• One-step atmospheric pressure synthesis of the ground state of Fe based LaFeAsO1-d superconductor
• Flux pinning mechanism in NdFeAsO0.82F0.18 superconductor: Thermally activated flux flow and charge carrier mean free path fluctuation pinning
• In Vitro Studies of Cells Grown on the Superconductor PrOxFeAs