Laser beams are crossed in a two-dimensional colloidal liquid of strongly interacting spherical particles to produce an external periodic potential and stimulate a density modulation. If the modulation wave vector is at the peak in the static structure factor, a sufficiently large potential induces a phase transition to a structure which exhibits solidlike order having density modes other than those directly excited. A Landau theory is presented and discussed in terms of our results.

• Received 3 June 1985

DOI:https://doi.org/10.1103/PhysRevLett.55.833