Observation of the Coupling of Concentration Fluctuations to Steady-State Shear Flow

This Letter reports the first experimental study of the spatial structure of spontaneous thermal fluctuations for $\mathrm{ka}\gtrsim 1$ in a physical system maintained in a nonequilibrium steady state. In particular, the shear-flow-induced distortion of the static structure factor, $\mathcal{S}\left(\overrightarrow{\mathrm{k}}\right)$, is observed for a colloidal suspension of strongly interacting spherical particles of interparticle separation $a$.