Disorder and Phase Transitions
Glass, a Solid or a Liquid ?
Glasses are solids insofar, as they are resistant to shear, in contrast to liquids. But in contrast to solids glasses do not have a regular internal order of atoms, glasses are amorphous. Because of this lacking long-range atomic order it is still not completely clear if the glassy state is thermodynamically different from a strongly supercooled liquid. Large scale computer-simulations of glasses have shown, that extended low-dimensional correlations exist within glasses. These structural correlations are responsible for anomalies in the vibrational spectra of glasses and for relaxational processes.
(C. Oligschleger, H.R. Schober, Phys. Rev. B 59, 811 (1999))
Dynamics of Glasses
Using computer simulations and analytic methods we study models and materials such as Se and CuZr. Cooling from the supercooled melt to the glass transition, diffusion and relaxation become strongly correlated. The atoms move in chain like structures, where single atoms typically move only a fraction of a nearest neighbour distance. These chain structures persit in the glass. Even at temperatures below 1K where one observes tunneling systems motion is collective. Collectivity of motion is intimately connected with the dynamic heterogeneity seen in glasses and under cooled melts.
(D. Caprion, J. Matsui, H.R. Schober, Phys. Rev. Lett. 85, 4293 (2000)).
Epitaxial Growth with Long-Range Interactions
We study a model for island formation in submonolayer epitaxy in the presence of a long-range elastic interaction between the adsorbed particles. The interaction is caused by the deformation of the underlying substrate and has a repulsive 1/r^3 character. The atoms perform a random walk until they attach irreversibly to an island. With increasing elastic repulsion, island nucleation is hampered and deferred to higher coverage values. We obtain a scaling law relating particle flux, particle mobility and elastic interaction strength.
(F. Gutheim, H. Müller-Krumbhaar, E. Brener. Epitaxial growth with elastic interaction: Submonolayer island formation Phys. Rev. E, vol. 63, 041603 (2001)).
Phase Transitions with Elastic Effects
Phase transitions of alloys are usually accompanied by strong temperature gradients and lattice misfits between the different components. They can induce elastic deformations which strongly alter the growth and coarsening behavior. Especially for melting and crystallization processes the appearing new phases are no longer spherical but have more complicated disk-like shapes. Strong interactions between adjacent inclusions lead to new physical features.
(E. Brener, V. Marchenko, H. Müller-Krumbhaar, and R. Spatschek, Coarsening Kinetics with Elastic Effects, Phys. Rev. Lett. 84, 4914 (2000)).