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 in the generators of SU(3) group (Gell-Mann matrices). The knowledge of such group structure allows us to obtain some new exact analytical results. Analysing the proper classical model we arrive at 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.