Direct imaging of the three-dimensional structure of a system of particles suspended in a dusty plasma reveals coexisting bcc and simple-hexagonal crystal structures. The coexistence is attributed to a bistability which appears in a recent theory predicting an attractive region in the plasma downstream of a particle in an ion flow. Both structures are polycrystalline, and they have short-range translational but quasi-long-range orientational order within a grain. This ordering is characteristic of the two-dimensional hexatic phase, but the existence of grain boundaries is not. © 1996 The American Physical Society.

• Received 24 January 1996

DOI:https://doi.org/10.1103/PhysRevE.54.5636