Chapter 24 - Fluctuations in Condensed Matter

Abstract

All condensed matter systems at finite temperature exhibit fluctuations over time and space. Thermodynamic properties such as heat capacity and thermal expansion coefficient can be directly calculated from the variance of these fluctuations. In addition, transport properties such as diffusivity and viscosity can be calculated from time correlation functions using the Green-Kubo relation and linear response theory. In broken ergodic systems, the variance of fluctuations is different in the time and ensemble domains. Condensed systems exhibit spatial variations in relaxation time scales known as dynamical heterogeneities. Dynamical heterogeneities can be calculated using molecular dynamics simulations in the isoconfigurational ensemble. Owing to such localized differences in kinetics, the relaxation of density fluctuations exhibits a nonmonotonic decay behavior. Control of fluctuations is critical for many industrial materials, such as high performance display glass substrates, where the relaxation magnitude must be controlled to be as consistent as possible. One strategy to minimize fluctuations in the relaxation behavior of a glass is to use compositions having higher fragility of the corresponding supercooled liquid state.