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

By F. Hunte, J. Jaroszynski, A. Gurevich, D. Larbalestier, R. Jin, A. Sefat, M. McGuire, B. Sales, D. Christen, D. Mandrus. 2008

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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.

Subfields: Accounting, Electronic, Optical and Magnetic Materials

View Paper: https://www.semanticscholar.org/paper/003d5876dd5be43afeea1bb1217e9ca2513bd7c2