Phase behavior of colloidal monolayers in quasiperiodic light fields

We experimentally investigate the phase behavior of a dense two-dimensional system of interacting colloidal particles subjected to a decagonal quasiperiodic potential landscape created by the interference of five laser beams. Upon increasing the intensity I-0 of the laser field, we observe the initial triangular crystal to change into a quasicrystal via a two-step process. To characterize this transition, we apply an algorithm that describes the resulting structures in terms of a polygonal tiling comprised of triangular, square and pentagonal tiles. First, square tiles develop at the expense of triangular tiles and assemble into bands. Only at higher laser intensities, pentagonal tiles, which reflect the decagonal quasiperiodic ordering, occur. For certain particle densities, an Archimedean-like tiling occurs where the bands of square extend across the entire system. We demonstrate how the alignment of these bands can be related to phasonic strain fields in the laser pattern.