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Symmetry 2012, 4(1), 251-264; doi:10.3390/sym4010251

One-Sign Order Parameter in Iron Based Superconductor

Leibniz-Institute for Solid State Research, IFW-Dresden, D-01171 Dresden, Germany
Institute for Metal Physics, 03142 Kyiv, Ukraine
Diamond Light Source Ltd., Didcot, Oxfordshire, OX11 0DE, UK
Moscow State University, 119991 Moscow, Russia
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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MDPI and ACS Style

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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