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An Application of the Extended Global SO(3) × SO(3) × U(1) Symmetry of the Hubbard Model on a Square Lattice: The Spinon, η-Spinon, and c Fermion Description
Symmetry 2012, 4(1), 251-264; doi:10.3390/sym4010251

One-Sign Order Parameter in Iron Based Superconductor

1,* , 1
1 Leibniz-Institute for Solid State Research, IFW-Dresden, D-01171 Dresden, Germany 2 Institute for Metal Physics, 03142 Kyiv, Ukraine 3 Diamond Light Source Ltd., Didcot, Oxfordshire, OX11 0DE, UK 4 Moscow State University, 119991 Moscow, Russia 5 Helmholtz-Zentrum Berlin, BESSY, D-12489 Berlin, Germany
* Author to whom correspondence should be addressed.
Received: 2 March 2012 / Revised: 14 March 2012 / Accepted: 16 March 2012 / Published: 21 March 2012
(This article belongs to the Special Issue Symmetries of Electronic Order)
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The onset of superconductivity at the transition temperature is marked by the onset of order, which is characterized by an energy gap. Most models of the iron-based superconductors find a sign-changing (s±) order parameter [1–6], with the physical implication that pairing is driven by spin fluctuations. Recent work, however, has indicated that LiFeAs has a simple isotropic order parameter [7–9] and spin fluctuations are not necessary [7,10], contrary to the models [1–6]. The strength of the spin fluctuations has been controversial [11,12], meaning that the mechanism of superconductivity cannot as yet be determined. We report the momentum dependence of the superconducting energy gap, where we find an anisotropy that rules out coupling through spin fluctuations and the sign change. The results instead suggest that orbital fluctuations assisted by phonons [13,14] are the best explanation for superconductivity.
Keywords: iron-based superconductors; ARPES; LiFeAs; order parameter iron-based superconductors; ARPES; LiFeAs; order parameter
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Borisenko, S.V.; Zabolotnyy, V.B.; Kordyuk, A.A.; Evtushinsky, D.V.; Kim, T.K.; Morozov, I.V.; Follath, R.; Büchner, B. One-Sign Order Parameter in Iron Based Superconductor. Symmetry 2012, 4, 251-264.

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