Muon spin rotation measurement of the magnetic field penetration depth in Ba(Fe0.926Co0.074)2As2: Evidence for multiple superconducting gaps

T. J. Williams, A. A. Aczel, E. Baggio-Saitovitch, S. L. Bud’ko, P. C. Canfield, J. P. Carlo, T. Goko, J. Munevar, N. Ni, Y. J. Uemura, W. Yu, and G. M. Luke
Phys. Rev. B 80, 094501 – Published 2 September 2009

Abstract

We have performed transverse field muon spin rotation measurements of single crystals of Ba(Fe0.926Co0.074)2As2 with the applied magnetic field along the ĉ direction. Fourier transforms of the measured spectra reveal an anisotropic line-shape characteristic of an Abrikosov vortex lattice. We have fit the μSR spectra to a microscopic model in terms of the penetration depth λ and the Ginzburg-Landau parameter κ. We find that as a function of temperature, the penetration depth varies more rapidly than in standard weak-coupled BCS theory. For this reason we first fit the temperature dependence to a power law where the power varies from 1.6 to 2.2 as the field changes from 0.02 to 0.1 T. Due to the surprisingly strong field dependence of the power and the superfluid density we proceeded to fit the temperature dependence to a two-gap model, where the size of the two gaps is field independent. From this model, we obtained gaps of 2Δ1=3.77kBTC and 2Δ2=1.57kBTC, corresponding to roughly 6 and 3 meV, respectively.

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  • Received 20 May 2009

DOI:https://doi.org/10.1103/PhysRevB.80.094501

©2009 American Physical Society

Authors & Affiliations

T. J. Williams1, A. A. Aczel1, E. Baggio-Saitovitch2, S. L. Bud’ko3, P. C. Canfield3, J. P. Carlo4, T. Goko1,4,5, J. Munevar2, N. Ni3, Y. J. Uemura4, W. Yu6, and G. M. Luke1,7,*

  • 1Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada L8S 4M1
  • 2Centro Brasileiro de Pesquisas Fisicas, Rua Xavier Sigaud 150 Urca, Rio de Janeiro CEP 22290-180, RJ, Brazil
  • 3Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
  • 4Department of Physics, Columbia University, New York, New York 10027, USA
  • 5TRIUMF, Vancouver, British Columbia, Canada V6T 2A3
  • 6Department of Physics, Renmin University of China, Beijing 100872, China
  • 7Canadian Institute of Advanced Research, Toronto, Ontario, Canada M5G 1Z8

  • *Author to whom correspondence should be addressed; luke@mcmaster.ca

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Vol. 80, Iss. 9 — 1 September 2009

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