Crossover from spin waves to diffusive spin excitations in underdoped Ba(Fe1-xCox)2As2

G. S. Tucker, R. M. Fernandes, D. K. Pratt, A. Thaler, N. Ni, K. Marty, A. D. Christianson, M. D. Lumsden, B. C. Sales, A. S. Sefat, S. L. Bud'Ko, P. C. Canfield, A. Kreyssig, A. I. Goldman, R. J. McQueeney

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Using inelastic neutron scattering, we show that the onset of superconductivity in underdoped Ba(Fe1-xCox)2As2 coincides with a crossover from well-defined spin waves to overdamped and diffusive spin excitations. This crossover occurs despite the presence of long-range stripe antiferromagnetic order for samples in a compositional range from x=0.04 to 0.055, and is a consequence of the shrinking spin-density wave gap and a corresponding increase in the particle-hole (Landau) damping. The latter effect is captured by a simple itinerant model relating Co doping to changes in the hot spots of the Fermi surface. We argue that the overdamped spin fluctuations provide a pairing mechanism for superconductivity in these materials.

Original languageEnglish (US)
Article number180503
JournalPhysical Review B - Condensed Matter and Materials Physics
Issue number18
StatePublished - May 13 2014

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