Dipole and quadrupole skyrmions in S=1 (pseudo)spin systems

Abstract

In terms of spin coherent states we have investigated topological defects in 2D S=1 (pseudo)spin quantum system with the bilinear and biquadratic isotropic exchange in the continuum limit. The proper Hamiltonian of the model can be written as bilinear on the generators of SU(3) group (Gell-Mann matrices). Knowledge of such group structure enables us to obtain some new exact analytical results. The analysis of the proper classical model and its topology allows to get different skyrmionic solutions with finite energy and the spatial distribution of spin-dipole and/or spin-quadrupole moments termed as dipole, quadrupole, and dipole–quadrupole skyrmions, respectively. Among the latter we would like note the in-plane vortices with the in-plane distribution of spin moment, varying spin length, and the non-trivial distribution of spin-quadrupole moments.