Global Symmetry, the Phonon Density of States and RUS
LOS ALAMOS NATIONAL LAB NM
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RUS measures in principle a complete set of the acoustic phonons near the Brillouin zone center. By comparison with a model of an homogeneous solid of known global symmetry and judicious application of a goodness-of-fit measure, the elastic constants can be deduced. For many solid state phase transitions the change in the symmetry of the object locally and globally is of prime importance, particularly where the transition leads to disorder at some length scale. We will discuss the application of RUS to determination of symmetry and whether in practice this can provide useful information on systems with fine or meso-scale structure. Such systems are in some sense intermediate between homogeneous single crystals low symmetry and an homogeneous, isotropic glassy state high symmetry. We expect this to be reflected in the behavior of the phonon density-of-states and thus into other physical properties such as the specific heat. We discuss the application of RUS to measuring this behavior directly or to guiding other experimental techniques which have access to different length scales. These topics will be illustrated by analyses of our RUS data on perovskite and martensite systems.
- Solid State Physics