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

TL;DR

This study uses inelastic neutron scattering to reveal anisotropic, quasi-two-dimensional magnetic excitations and unusual quasi-propagating spin excitations in superconducting Ba(Fe$_{0.926}$Co$_{0.074}$)$_2$As$_2$, highlighting spin nematic correlations.

Contribution

It provides new insights into the anisotropic spin excitations and their evolution into quasi-propagating modes in a superconducting iron pnictide.

Findings

Anisotropic magnetic excitations near the AFM wave-vector.

Spin resonance at ~8.3 meV shows the same anisotropy.

Unusual quasi-propagating excitations above 80 meV.

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}$_{\texttt{AFM}}=({1}{2}/{1}{2})$ - 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$8.3 meV in the SC state displays the same anisotropy. The anisotropic fluctuations experimentally evolve into two distinct maxima only along the direction transverse to \textbf{Q}$_{\texttt{AFM}}$ above $\sim$80 meV indicating unusual quasi-propagating excitations.