Real-Time Microscopy of Two-Dimensional Critical Fluctuations: Disordering of the Si(113)-( $3\times 1$) Reconstruction

Using low-energy electron microscopy, we have studied the critical fluctuations associated with the disordering of the $(3\times 1)$ reconstruction on Si(113). We not only observe and quantify the increased spatial correlations near $T_c$, but also the associated slowing down of the relaxation of long wavelength critical fluctuations. The dependence of the slowing down on correlation length is consistent with theories for phase transitions with nonconserved order parameters. In addition, we show that steps limit the size of the correlation length, as is often conjectured.