  We propose and demonstrate a method to achieve large effective Soret
coefficient in colloids by suitably mixing two different particles, e.g.,
silica beads and Fe3O4 nanoparticles. It is shown that the thermophoretic
motion of Fe3O4 nanoparticles out of the heating region results in a large
nonequlibrium depletion force for silica beads. Consequently, silica beads are
driven quickly to the heating region, forming a three-dimensional crystal with
few defects and dislocations. The binding of silica beads is so tight that a
colloidal photonic crystal can be achieved after the complete evaporation of
solvent, water. Thus, for fabrication of defect free colloidal PCs, periodic
structures for molecular sieves, among others, the proposed technique could be
a low cost alternative. In addition as we use biocompatible materials, this
technique could be a tool for biophysics studies where the potential of large
effective Soret coefficient could be useful.
