Transition from Sign-Reversed to Sign-Preserved Cooper-Paring Symmetry in Sulfur-Doped Iron Selenide Superconductors

Published

May 13, 2016

Author(s)

Qisi Wang, J. T. Park, Yu Feng, Yao Shen, Yiqing Hao, Bingying Pan, Jeffrey W. Lynn, A. Ivanov, Songxue Chi, M. Matsuda, Huibo Cao, R. J. Birgeneau, D.V. Efremov, Jun Zhao

Abstract

An essential step toward elucidating the mechanism of superconductivity is to determine the sign/phase of 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 (high-T_c) 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} u1-3^. Here, by using magnetic neutron scattering, a phase sensitive probe of superconducting gap⁴, we report the observation of a crossover 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. The 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^5-7.

Citation

Physical Review Letters

Volume

116

Issue

19

Pub Type

Journals

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Keywords

Iron Superconductor, Superconducting Pairing Symmetry, Neutron inelastic scattering

Citation

Wang, Q. , Park, J. , Feng, Y. , Shen, Y. , Hao, Y. , Pan, B. , Lynn, J. , Ivanov, A. , Chi, S. , Matsuda, M. , Cao, H. , Birgeneau, R. , Efremov, D. and Zhao, J. (2016), Transition from Sign-Reversed to Sign-Preserved Cooper-Paring Symmetry in Sulfur-Doped Iron Selenide Superconductors, Physical Review Letters, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=918841 (Accessed October 13, 2025)