Distinguishing ${s}^{\ifmmode\pm\else\textpm\fi{}}$ and ${s}^{++}$ electron pairing symmetries by neutron spin resonance in superconducting NaFe${}_{0.935}$Co${}_{0.045}$As

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Distinguishing $s^{\pm}$ and $s^{+ +}$ electron pairing symmetries by neutron spin resonance in superconducting NaFe $_{0.935}$ Co $_{0.045}$ As

Chenglin Zhang, H.-F. Li, Yu Song, Yixi Su, Guotai Tan, Tucker Netherton, Caleb Redding, Scott V. Carr, Oleg Sobolev, Astrid Schneidewind, Enrico Faulhaber, L. W. Harriger, Shiliang Li, Xingye Lu, Dao-Xin Yao, Tanmoy Das, A. V. Balatsky, Th. Brückel, J. W. Lynn, and Pengcheng Dai

Phys. Rev. B 88, 064504 – Published 9 August 2013

Abstract

A determination of the superconducting (SC) electron pairing symmetry forms the basis for establishing a microscopic mechanism for superconductivity. For iron pnictide superconductors, the $s^{\pm}$ -pairing symmetry theory predicts the presence of a sharp neutron spin resonance at an energy below the sum of hole and electron SC gap energies ( $E \leq 2 Δ$ ) below $T_{c}$ . On the other hand, the $s^{+ +}$ -pairing symmetry expects a broad spin excitation enhancement at an energy above $2 Δ$ below $T_{c}$ . Although the resonance has been observed in iron pnictide superconductors at an energy below $2 Δ$ consistent with the $s^{\pm}$ -pairing symmetry, the mode has also been interpreted as arising from the $s^{+ +}$ -pairing symmetry with $E \geq 2 Δ$ due to its broad energy width and the large uncertainty in determining the SC gaps. Here we use inelastic neutron scattering to reveal a sharp resonance at $E = 7$ meV in SC NaFe $_{0.935}$ Co $_{0.045}$ As ( $T_{c} = 18$ K). On warming towards $T_{c}$ , the mode energy hardly softens while its energy width increases rapidly. By comparing with calculated spin-excitation spectra within the $s^{\pm}$ and $s^{+ +}$ -pairing symmetries, we conclude that the ground-state resonance in NaFe $_{0.935}$ Co $_{0.045}$ As is only consistent with the $s^{\pm}$ pairing, and is inconsistent with the $s^{+ +}$ -pairing symmetry.

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Received 17 May 2013

DOI:https://doi.org/10.1103/PhysRevB.88.064504

Authors & Affiliations

Chenglin Zhang^1,2, H.-F. Li^3,4, Yu Song^1,2, Yixi Su⁵, Guotai Tan^6,2, Tucker Netherton², Caleb Redding², Scott V. Carr^1,2, Oleg Sobolev⁷, Astrid Schneidewind^5,8, Enrico Faulhaber^9,8, L. W. Harriger¹⁰, Shiliang Li¹¹, Xingye Lu¹¹, Dao-Xin Yao¹², Tanmoy Das¹³, A. V. Balatsky¹³, Th. Brückel¹⁴, J. W. Lynn¹⁰, and Pengcheng Dai^1,2,11,*

¹Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA
²Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996-1200, USA
³Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH, Outstation at Institut Laue-Langevin, Boı̂te Postale 156, F-38042 Grenoble Cedex 9, France
⁴Institut für Kristallographie der RWTH Aachen, 52056 Aachen, Germany
⁵Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH, Outstation at MLZ, D-85747 Garching, Germany
⁶Department of Physics, Beijing Normal University, Beijing 100875, China
⁷Institut für Physikalische Chemie, Georg-August-Universität Göttingen, Tammannstrasse 6, 37077 Göttingen, Germany
⁸Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM-II), TU München, D-85747 Garching, Germany
⁹Gemeinsame Forschergruppe HZB–TU Dresden, Helmholtz-Zentrum Berlin für Materialien und Energie, D-14109 Berlin, Germany
¹⁰NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
¹¹Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
¹²State Key Laboratory of Optoelectronic Materials and Technology, Sun Yat-Sen University, Guangzhou 510275, China
¹³Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, USA
¹⁴Jülich Centre for Neutron Science JCNS and Peter Grünberg Institut PGI, JARA-FIT, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

^*pdai@rice.edu

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Vol. 88, Iss. 6 — 1 August 2013

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Physical Review B

covering condensed matter and materials physics

Distinguishing $s^{\pm}$ and $s^{+ +}$ electron pairing symmetries by neutron spin resonance in superconducting NaFe $_{0.935}$ Co $_{0.045}$ As

Chenglin Zhang, H.-F. Li, Yu Song, Yixi Su, Guotai Tan, Tucker Netherton, Caleb Redding, Scott V. Carr, Oleg Sobolev, Astrid Schneidewind, Enrico Faulhaber, L. W. Harriger, Shiliang Li, Xingye Lu, Dao-Xin Yao, Tanmoy Das, A. V. Balatsky, Th. Brückel, J. W. Lynn, and Pengcheng Dai

Phys. Rev. B 88, 064504 – Published 9 August 2013

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Physical Review B

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Distinguishing s± and s++ electron pairing symmetries by neutron spin resonance in superconducting NaFe0.935Co0.045As

Chenglin Zhang, H.-F. Li, Yu Song, Yixi Su, Guotai Tan, Tucker Netherton, Caleb Redding, Scott V. Carr, Oleg Sobolev, Astrid Schneidewind, Enrico Faulhaber, L. W. Harriger, Shiliang Li, Xingye Lu, Dao-Xin Yao, Tanmoy Das, A. V. Balatsky, Th. Brückel, J. W. Lynn, and Pengcheng Dai

Phys. Rev. B 88, 064504 – Published 9 August 2013

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Distinguishing $s^{\pm}$ and $s^{+ +}$ electron pairing symmetries by neutron spin resonance in superconducting NaFe $_{0.935}$ Co $_{0.045}$ As