The quantitative details for the sequence of events we have described in the previous sections were obtained from the analysis of a single data run. The qualitative aspects including the identification of the stages of the phase transition were readily reproducible from run to run. In particular, the supercooled fluid formed by shear melting a confined lattice freezes extremely rapidly. The resulting crystal, however, has symmetry. One of the more surprising observations in this study is that this initial transformation goes virtually to completion although the result is not the system's equilibrium structure. The crystal displays a distinct soft phonon mode distortion into the third dimension. These buckling distortions form domains of differing orientation even within a single underlying triangular crystal. The buckled crystal undergoes a martensitic transition back to the structure. This shear-mediated transition is characterized by extensive and very rapid local order fluctuations. The martensitic transition enters a second slower phase once the local symmetry predominates and local misoriented domains have to compete. Misorientation of grains is the necessary outcome of shearing along different crystallographic axes of the crystal. Such processes are likely to be responsible for slowing and staging in the martensitic transitions of conventional materials.
We would like to acknowledge enlightening conversations with Stuart Rice, Andrew Marcus, and especially John Crocker who also wrote the tracking algorithm. We are also grateful to Art Hebard for preparing the -InO films. The work at The University of Chicago was supported by the National Science Foundation in part through Grant Number DMR-9320378 (DGG) and in part by the MRSEC Program of the National Science Foundation under Award Number DMR-9400379.