Figure 1
(a) The AF Fe spin ordering in BaFe
As
with the magnetic exchange couplings
,
,
along different directions. (b) Temperature dependence of the resistivity in detwinned BaFe
As
(from Ref.
14). The inset is a plot of the resistivity for the twinned sample used in our neutron measurements with the blue points corresponding to
, 125, and 150 K. (c) Color plots describing qualitatively how the spin wave scattering evolves from Q = (1, 0) to (1, 1) as a function of energy using an anisotropic damping Γ. The solid black contours are an overlay of the same model but with no damping. The exchange couplings used in both plots are from best fits of the data. (d) Color plot of the anisotropic damping Γ, which is much stronger along the
direction than along the
direction. (e) Spin wave dispersion along the (1,
) direction as determined by energy and Q cuts of the raw data in Fig. 2 below and above
. The solid line is a Heisenberg model calculation using anisotropic exchange couplings
± 2.0,
= −9.2 ± 1.2,
± 1.0,
± 0.3 meV determined by fitting the full cross section. The dotted line is a Heisenberg model calculation assuming isotropic exchange coupling
=
± 1.4,
= 28.7 ± 0.5, and
meV. (f) Dispersion along the (
, 0) direction; data points beyond
could not be reliably obtained due to strong damping at higher energies. The red shading stresses how the damping grows as a function of
. Error bars are systematic and represent the difference between Q and
cut dispersion points. The statistical error of the Q and
cuts are much smaller.
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