Correlation length and dimensional crossover in a quasi-one-dimensional surface system

The strongly anisotropic adsorbate system Br/Pt(110) exhibits an anomalous order-order phase transition due to competition between interadsorbate repulsion and charge densitywave (CDW) correlations. The phase transition is preceded by fluctuations between a normal c(2 x 2) adsorbate phase on a flat surface and a (2 x 1) phase involving a periodic lattice distortion of the substrate. Here we study the fluctuations, determine the correlation length in real and reciprocal space, and report its evolution with temperature. This allows us to identify a critical temperature. However, since around the critical temperature the adsorbate mobility freezes out, the transition remains incomplete, resulting in a 2D nematic glass at low temperature. In the temperature range, where the fluctuations occur, the system is demonstrated to be close to a 1D -> 2D crossover. This unusual phase transition driven by competing interactions exhibits several parallels to phenomena observed in unconventional superconductors.