paper

Anisotropic and quasipropagating spin excitations in superconducting Ba(Fe0.926Co0.074)2As2

arXiv:1003.1687 · doi:10.1103/PhysRevB.82.140503

Abstract

Inelastic neutron scattering from superconducting (SC) Ba(Fe $_{0.926}$ Co $_{0.074}$ ) $_{2}$ As $_{2}$ reveals anisotropic and quasi-two-dimensional (2D) magnetic excitations close to \textbf{Q} $_{AFM} = (12 / 12)$ - the 2D antiferromagnetic (AFM) wave-vector of the parent BaFe $_{2}$ As $_{2}$ compound. The correlation length anisotropy of these low energy fluctuations is consistent with spin nematic correlations in the $J_{1}$ - $J_{2}$ model with $J_{1} / J_{2} \sim$ 1. The spin resonance at $\sim$ 8.3 meV in the SC state displays the same anisotropy. The anisotropic fluctuations experimentally evolve into two distinct maxima only along the direction transverse to \textbf{Q} $_{AFM}$ above $\sim$ 80 meV indicating unusual quasi-propagating excitations.

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