T. Bodineau, E. Presutti
Surface tension and Wulff shape for a lattice model without 
spin flip symmetry.
(952K, Postscript)

ABSTRACT.  We propose a new definition of surface tension and check it in a spin model of the 
Pirogov-Sinai class where the spin flip symmetry is broken. We study the model at low 
temperatures on the phase transitions line and prove: 
(i) existence of the surface tension in the thermodynamic limit, for any orientation 
of the surface and in all dimensions $d\ge 2$; 
(ii) the Wulff shape constructed with such a surface tension coincides with the 
equilibrium shape of the cluster which appears when fixing the total spin 
magnetization (Wulff problem).