Inelastic Neutron Scattering Study of a Nonmagnetic Collapsed Tetragonal Phase in NonsuperconductingCaFe2As2: Evidence of the Impact of Spin Fluctuations on Superconductivity in the Iron-Arsenide Compounds

Abstract

The relationship between antiferromagnetic spin fluctuations and superconductivity has become a central topic of research in studies of superconductivity in the iron pnictides. We present unambiguous evidence of the absence of magnetic fluctuations in the nonsuperconducting collapsed tetragonal phase of CaFe2As2 via inelastic neutron scattering time-of-flight data, which is consistent with the view that spin fluctuations are a necessary ingredient for unconventional superconductivity in the iron pnictides. We demonstrate that the collapsed tetragonal phase of CaFe2As2 is nonmagnetic, and discuss this result in light of recent reports of high-temperature superconductivity in the collapsed tetragonal phase of closely related compounds.

Combined effects of post-growth thermal treatment and chemical substitution on physical properties of CaFe₂As₂

“…The absence of the superconductivity in the cT phase region is consistent with the idea that the mechanism of iron-based superconductor depends on magnetic fluctuations (Mazin et al, 2008;. Since in the cT phase magnetic moment is quenched completely, there is no spin fluctuation to drive the superconducting phase (Pratt et al, 2009b;Soh et al, 2013;Dhaka et al, 2014;Furukawa et al, 2014).…”

Low-temperature nuclear magnetic resonance investigation of systems frustrated by competing exchange interactions

“…Thus we conclude that strong AFM spin fluctuations are realized in the HT T phase in both the "annealed" and "as-grown" CaFe 2 As 2 crystals, consistent with INS measurements On the contrary since we do not observe any signature of AFM correlations in LT c−T phase either from the T dependence of 1/T 1 T χ or from the NMR spectrum, we conclude that electron correlations melt in this phase. This is consistent with inelastic neutron scattering measurements [173][186] and with the results of ARPES [190], both of which demonstrate the evidence of the absence of magnetic fluctuations in the nonsuperconducting c−T phase in CaFe 2 As 2 .…”

Antiferromagnetic order and spin dynamics in iron-based superconductors

“…The local moments in the Nd-and Pr-doped samples disappear in the cT phase , indicating that the Fe 2+ ions go through a spin-state transition by taking on the low-spin state in the cT phase. Inelastic neutron scattering experiments on CaFe 2 As 2 also reveal vanishing spin excitations in the cT phase (Soh et al, 2013), Large symbols: estimates of doping-dependent energy scale at which magnetic spectral weight falls below half that of the AF state based on inelastic neutron scattering studies of various cuprates (Stock et al, 2010a). Small gray symbols: pseudogap energy from various electronic spectroscopies .…”