Physics – Condensed Matter – Disordered Systems and Neural Networks
Scientific paper
2001-05-21
Physics
Condensed Matter
Disordered Systems and Neural Networks
26 pages 24 figures
Scientific paper
10.1103/PhysRevE.64.051505
We investigate the dynamics of a fluid of dipolar hard spheres in its liquid and glassy phase, with emphasis on the microscopic time or frequency regime. This system shows rather different glass transition scenarios related to its rich equilibrium behavior which ranges from a simple hard sphere fluid to a long range ferroelectric orientational order. In the liquid phase close to the ideal glass transition line and in the glassy regime a medium range orientational order occurs leading to a softening of an orientational mode. To investigate the role of this mode we use the molecular mode-coupling equations to calculate the spectra $\phi_{lm}^{\prime \prime}(q,\omega)$ and $\chi _{lm}''(q,\omega)$. In the center of mass spectra $ \phi_{00}''(q,\omega)$ and $\chi_{00}''(q,\omega)$ we found besides a high frequency peak at $\omega _{hf}$ a peak at $\omega_{op}$, about one decade below $\omega_{hf}$. $\omega _{op}$ has almost no $q$-dependence and exhibits an ``isotope'' effect $\omega _{op}\propto I^{-1/2}$, with $I$ the moment of inertia. We give evidence that the existence of this peak is related to the occurrence of the medium ranged orientational order. It is shown that some of these feature also exist for schematic mode coupling models.
Latz Arnulf
Letz M.
Schilling Rene
Theenhaus Th.
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