Phase Boundary and Soliton Excitation in the XY Model with Competing Interactions in Twofold Field

Abstract

The ground state of the XY model with competing interaction, which is reduced to the axial next nearest neighbour Ising model at a limit of infinite value of strength of twofold field, is studied from the viewpoint of solitons. Excitation energies of compressed and stretched solitons at phases with periods 6, 5 and 7 are obtained by numerical analysis of periodic states, from which phase boundaries are determined. Each of these phases is shown to have a finite stable range, which indicates that the ground state of the model has a type of devil's staircase structure.