Berlin 2008 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 29: Poster II
DY 29.5: Poster
Thursday, February 28, 2008, 16:00–18:00, Poster C
Crossover from attractive to repulsive thermodynamic Casimir forces — •Felix Schmidt and Hans Werner Diehl — Fachbereich Physik, Universität Duisburg-Essen, D-47048 Duisburg
Films whose long-length-scale behavior near the bulk critical point is described by n-vector φ4-models in slab geometries with free surfaces are considered. The confining surfaces are presumed to preserve the O(n) invariance of the Hamiltonian. Local enhancements or weakenings of the pair interactions at the two boundary planes B1 at z=0 and B2 at z=L are allowed and taken into account through quadratic surface contributions with different interaction constants c1≥ 0 and c2≥ 0 on B1 and B2, respectively. When c1≠ c2, the thermodynamic Casimir force that occurs near the bulk critical temperature can be repulsive or attractive. Using the field-theoretical renormalization group in d=4−є dimensions, the thermodynamic Casimir force is determined at and near the bulk critical temperature for general positive values of c1 and c2. For appropriate choices of c1−c2, crossovers from attractive to repulsive Casimir interactions (or vice versa) occur as the bulk critical temperature is approached.