title: Casimir force in the rotor model with twisted boundary conditions.
abstract: We investigate the three-dimensional lattice XY model with nearest neighbor interaction. The vector order parameter of this system lies on the vertices of a cubic lattice, which is embedded in a system with a film geometry. The orientations of the vectors are fixed at the two opposite sides of the film. The angle between the vectors at the two boundaries is α where 0≤α≤π. We make use of the mean field approximation to study the mean length and orientation of the vector order parameter throughout the film--and the Casimir force it generates--as a function of the temperature T, the angle α, and the thickness L of the system. Among the results of that calculation are a Casimir force that depends in a continuous way on both the parameter α and the temperature and that can be attractive or repulsive. In particular, by varying α and/or T one controls both the sign and the magnitude of the Casimir force in a reversible way. Furthermore, for the case α=π, we discover an additional phase transition occurring only in the finite system associated with the variation of the orientations of the vectors.
authors.affiliation: Department of Physics and Astronomy, UCLA, Los Angeles, California 90095-1547, USA. jbergk@physics.ucla.edu
authors.forename: Jonathan
authors.initials: J
authors.lastname: Bergknoff
authors.forename: Daniel
authors.initials: D
authors.lastname: Dantchev
authors.forename: Joseph
authors.initials: J
authors.lastname: Rudnick