Imaging Anomalous Nematic Order and Strain in Optimally Doped BaFe_{2}(As,P)_{2}.

We present the strain and temperature dependence of an anomalous nematic phase in optimally doped BaFe_{2}(As,P)_{2}. Polarized ultrafast optical measurements reveal broken fourfold rotational symmetry in a temperature range above T_{c} in which bulk probes do not detect a phase transition. Using ultrafast microscopy, we find that the magnitude and sign of this nematicity vary on a 50-100  μm length scale, and the temperature at which it onsets ranges from 40 K near a domain boundary to 60 K deep within a domain.