SKYRMION EXCITATIONS IN QUANTUM HALL SYSTEMS

Using finite-size calculations on the surface of a sphere we study the topological (Skyrmion) excitation in quantum Hall systems with spin d egrees of freedom at filling factors around nu=1. In the absence of Ze eman energy, we find, in systems with one quasiparticle or one quasiho le, the lowest-energy band consists of states with L=S, when L and S a re the total orbital and spin angular momentum. These different spin s tates are almost degenerate in the thermodynamic limit and their symme try-breaking ground state is the state with one Skyrmion of infinite s ize. In the presence of Zeeman energy, the Skyrmion size is determined by the interplay of the Zeeman energy and the electron-electron inter action and the Skyrmion shrinks to a spin texture of finite size. We h ave calculated the energy gap of the system at infinite wave-vector li mit as a function of the Zeeman energy and find there are kinks in the energy gap associated with the shrinking of the size of the Skyrmion.