A new boundary-controlled phase transition: Phase separation in an Ising bi-pyramid with competing surface fieldsA. Milchev1, 2, M. Müller1, 3 and K. Binder1
1 Institut für Physik, WA331, Johannes Gutenberg-Universität 55099 Mainz, Germany
2 Institute for Physical Chemistry, Bulgarian Academy of Sciences 1113 Sofia, Bulgaria
3 Department of Physics, University of Wisconsin-Madison 1150 University Avenue, Madison, WI 53706-1390, USA
received 1 February 2005; accepted in final form 18 March 2005
published online 8 April 2005
We study phase coexistence of an Ising ferromagnet in a bi-pyramid geometry with a square basal plane of linear extension 2L+1. Antisymmetric surface fields act on the pyramid surfaces above and below the basal plane. In the limit , the magnetisation stays zero at the bulk critical temperature, but becomes discontinuously non-zero at the cone filling critical temperature associated with a single pyramid. Monte Carlo simulations and scaling considerations show that this transition is described by a Landau theory with size-dependent coefficients that give rise to singular critical amplitudes.
68.08.Bc - Wetting.
05.70.Fh - Phase transitions: general studies.
68.35.Rh - Phase transitions and critical phenomena.
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