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Title: On the superconducting symmetry of Fe-based systems — Impurity effect studies and neutron scattering measurements-

To identify the superconducting symmetry of Fe-based superconductors, we studied effects of nonmagnetic-impurities on Tc, magnetic excitation spectra x" and NMR 1/T1 - T curve, which are sensitive to the relative signs between the order parameters on the disconnected Fermi surfaces in reciprocal space, because the symmetry is closely connected with the pairing mechanism: If the signs are opposite (symmetry S±), the mechanism is considered to be a magnetic one, but when the signs are the same (symmetry S++), a novel mechanism is plausible because the ordinary phonon mechanism cannot realize the Tc value as high as ~55 K found in Ln1111 (Ln=lanthanide). Results are as follows: (a) The very small rates of Tc-suppression by impurity atoms M of LnFe1-yMyAs0.89-xF0.11+x (M=Ni, Co, Ru) can be explained only by S++. (b) The x"-data for Ba(Fe, Co)2As2 (Tc ~ 23 K) and Ca-Fe-Pt-As crystals seem to be well explained by S++ rather than by S±. (c) The nuclear magnetic resonance data can be consistently understood by S++, too. These results suggest the S++ symmetry and a novel pairing mechanism, which can be considered to be related to the elastic softening of C66 induced by the orbital fluctuation of the system.
Authors:
 [1] ;  [2] ;  [2] ;  [2] ;  [2] ;  [2] ;  [3] ;  [3] ;  [4] ;  [5]
  1. Comprehensive Research Organization for Science and Society, Ibaraki (Japan); Nagoya Univ. (Japan). Graduate School of Science
  2. Nagoya Univ. (Japan)
  3. Comprehensive Research Organization for Science and Society, Ibaraki (Japan)
  4. Japan Atomic Energy Agency (JAEA), Ibaraki (Japan)
  5. Centre CEA of Saclay (France)
Publication Date:
OSTI Identifier:
1319154
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Journal of the Korean Physical Society
Additional Journal Information:
Journal Volume: 62; Journal Issue: 12; Journal ID: ISSN 0374-4884
Publisher:
Korean Physical Society
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). High Flux Isotope Reactor (HFIR); Spallation Neutron Source
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 47 OTHER INSTRUMENTATION Fe pnictide superconductors; magnetic excitation spectra; superconducting symmetry; impurity effects; NMR