Berlin 2015 – wissenschaftliches Programm
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DY: Fachverband Dynamik und Statistische Physik
DY 15: Statistical Physics - general
DY 15.8: Vortrag
Dienstag, 17. März 2015, 11:30–11:45, BH-N 334
Critical adsorption and Casimir forces in systems with a globally constrained order parameter — •Markus Gross1,2, Oleg Vasilyev1,2, and Siegfried Dietrich1,2 — 1Max-Planck-Institut für Intelligente Systeme, Heisenbergstrasse 3, 70569 Stuttgart, Germany — 2Institut für Theoretische Physik IV, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany
Typically, critical phenomena are investigated in the grand canonical ensemble, in which the order parameter is free to fluctuate without constraints. However, confining systems with a locally conserved order parameter -- such as fluids in a closed environment -- imposes a global constraint on the order parameter and thereby changes its fluctuation spectrum. This situation is naturally encountered in particle- or hydrodynamics-based simulations, such as Molecular Dynamics or Lattice Boltzmann methods. Here, we explore the consequences of the global order-parameter conservation on critical adsorption at walls and critical Casimir forces in a fluid film. Analytical calculations have been performed within mean-field theory as well as statistical field theory of a Ginzburg-Landau model. These results are confronted with Monte-Carlo simulations of the Ising model. Depending on the boundary conditions, the constraint is found to induce significant changes in the shape of the order-parameter profile of the adsorbed fluid. For instance, within mean field theory the divergence of the order parameter at the wall is cut-off. For certain boundary conditions, the Casimir force experienced by the critical film can have a drastically different temperature dependence as a consequence of the constraint.