Boundary field induced first order transition in the 2D Ising model: Exact study

Abstract. We present in this paper an exact study concerning a first order transition induced by an inhomogeneous boundary magnetic field in the 2D Ising model. From a previous analysis of the interfacial free energy in the discrete case (J. Phys. A: Math. Gen. 38, 2849, 2005), we identify, using an asymptotic expansion in the thermodynamic limit, the transition line that separates the regime where the interface is localised near the boundary from the regime where it is propagating inside the bulk. In particular, the critical line has a strong dependence on the aspect ratio of the lattice. Generalisation to other interfacial problems is discussed.