  We consider the role of potential scatterers in the nematic phase of Fe-based
superconductors above the transition temperature to the (pi,0) magnetic state
but below the orthorhombic structural transition. The anisotropic spin
fluctuations in this region can be frozen by disorder, to create elongated
magnetic droplets whose anisotropy grows as the magnetic transition is
approached. Such states act as strong anisotropic defect potentials which
scatter with much higher probability perpendicular to their length than
parallel, although the actual crystal symmetry breaking is tiny. We calculate
the scattering potentials, relaxation rates, and conductivity in this region,
and show that such emergent defect states are essential for the transport
anisotropy observed in experiments.
