Physics Colloquium, 28 November, 2000

Critical Casimir Effects

Moses Chan

Penn State University

The thermodynamic properties of a bulk system near its critical point are dominated by the diverging correlation length, which measures the spatial extent of the order parameter fluctuations. For a finite system such as a liquid film adsorbed on a solid substrate, the fluctuations are limited to the thickness of the film. Just as the cutoff of electromagnetic zero-point fluctuations leads to a distance dependent energy in the Casimir effect, this cutoff of the order parameter fluctuations translates to a thickness-dependent free energy, which is predicted to perturb the equilibrium thickness of a wetted film. In this talk, I will present measurements that verify the existence of fluctuation induced thinning of He-4 film close to the lambda point and thickening of the helium mixture film near the tricritical point.

3.30 p.m., Smith Laboratory, Room 1005

Refreshments served in Smith 1094 at 3:00 p.m.