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Title: Transition from Sign-Reversed to Sign-Preserved Cooper-Pairing Symmetry in Sulfur-Doped Iron Selenide Superconductors

Here, an essential step toward elucidating the mechanism of superconductivity is to determine the sign or phase of the superconducting order parameter, as it is closely related to the pairing interaction. In conventional superconductors, the electron-phonon interaction induces attraction between electrons near the Fermi energy and results in a sign-preserved s-wave pairing. For high-temperature superconductors, including cuprates and iron-based superconductors, prevalent weak coupling theories suggest that the electron pairing is mediated by spin fluctuations which lead to repulsive interactions, and therefore that a sign-reversed pairing with an s± or d-wave symmetry is favored. Here, by using magnetic neutron scattering, a phase sensitive probe of the superconducting gap, we report the observation of a transition from the sign-reversed to sign-preserved Cooper-pairing symmetry with insignificant changes in T c in the S-doped iron selenide superconductors K xFe 2-y(Se 1-zS z) 2. We show that a rather sharp magnetic resonant mode well below the superconducting gap (2Δ) in the undoped sample (z=0) is replaced by a broad hump structure above 2Δ under 50% S doping. These results cannot be readily explained by simple spin fluctuation-exchange pairing theories and, therefore, multiple pairing channels are required to describe superconductivity in this system. Our findings maymore » also yield a simple explanation for the sometimes contradictory data on the sign of the superconducting order parameter in iron-based materials.« less
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [1] ;  [1] ;  [3] ;  [4] ;  [5] ;  [5] ;  [5] ;  [6] ;  [7] ;  [1]
  1. Fudan Univ., Shanghai (China)
  2. Technishe Univ. Munchen, Garching (Germany)
  3. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
  4. Institut Laue-Langevin, Grenoble Cedex (France)
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  6. Univ. of California, Berkeley, CA (United States)
  7. IFW Dresden, Dresden (Germany)
Publication Date:
Grant/Contract Number:
AC02-05CH11231; AC03-76SF008
Type:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 116; Journal Issue: 19; Related Information: © 2016 American Physical Society.; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
OSTI Identifier:
1466695
Alternate Identifier(s):
OSTI ID: 1253071

Wang, Qisi, Park, J. T., Feng, Yu, Shen, Yao, Hao, Yiqing, Pan, Bingying, Lynn, J. W., Ivanov, A., Chi, Songxue, Matsuda, M., Cao, Huibo, Birgeneau, R. J., Efremov, D. V., and Zhao, Jun. Transition from Sign-Reversed to Sign-Preserved Cooper-Pairing Symmetry in Sulfur-Doped Iron Selenide Superconductors. United States: N. p., Web. doi:10.1103/PhysRevLett.116.197004.
Wang, Qisi, Park, J. T., Feng, Yu, Shen, Yao, Hao, Yiqing, Pan, Bingying, Lynn, J. W., Ivanov, A., Chi, Songxue, Matsuda, M., Cao, Huibo, Birgeneau, R. J., Efremov, D. V., & Zhao, Jun. Transition from Sign-Reversed to Sign-Preserved Cooper-Pairing Symmetry in Sulfur-Doped Iron Selenide Superconductors. United States. doi:10.1103/PhysRevLett.116.197004.
Wang, Qisi, Park, J. T., Feng, Yu, Shen, Yao, Hao, Yiqing, Pan, Bingying, Lynn, J. W., Ivanov, A., Chi, Songxue, Matsuda, M., Cao, Huibo, Birgeneau, R. J., Efremov, D. V., and Zhao, Jun. 2016. "Transition from Sign-Reversed to Sign-Preserved Cooper-Pairing Symmetry in Sulfur-Doped Iron Selenide Superconductors". United States. doi:10.1103/PhysRevLett.116.197004. https://www.osti.gov/servlets/purl/1466695.
@article{osti_1466695,
title = {Transition from Sign-Reversed to Sign-Preserved Cooper-Pairing Symmetry in Sulfur-Doped Iron Selenide Superconductors},
author = {Wang, Qisi and Park, J. T. and Feng, Yu and Shen, Yao and Hao, Yiqing and Pan, Bingying and Lynn, J. W. and Ivanov, A. and Chi, Songxue and Matsuda, M. and Cao, Huibo and Birgeneau, R. J. and Efremov, D. V. and Zhao, Jun},
abstractNote = {Here, an essential step toward elucidating the mechanism of superconductivity is to determine the sign or phase of the superconducting order parameter, as it is closely related to the pairing interaction. In conventional superconductors, the electron-phonon interaction induces attraction between electrons near the Fermi energy and results in a sign-preserved s-wave pairing. For high-temperature superconductors, including cuprates and iron-based superconductors, prevalent weak coupling theories suggest that the electron pairing is mediated by spin fluctuations which lead to repulsive interactions, and therefore that a sign-reversed pairing with an s± or d-wave symmetry is favored. Here, by using magnetic neutron scattering, a phase sensitive probe of the superconducting gap, we report the observation of a transition from the sign-reversed to sign-preserved Cooper-pairing symmetry with insignificant changes in Tc in the S-doped iron selenide superconductors KxFe2-y(Se1-zSz)2. We show that a rather sharp magnetic resonant mode well below the superconducting gap (2Δ) in the undoped sample (z=0) is replaced by a broad hump structure above 2Δ under 50% S doping. These results cannot be readily explained by simple spin fluctuation-exchange pairing theories and, therefore, multiple pairing channels are required to describe superconductivity in this system. Our findings may also yield a simple explanation for the sometimes contradictory data on the sign of the superconducting order parameter in iron-based materials.},
doi = {10.1103/PhysRevLett.116.197004},
journal = {Physical Review Letters},
number = 19,
volume = 116,
place = {United States},
year = {2016},
month = {5}
}