Landau-level mixing and skyrmion stability in quantum Hall ferromagnets

We present a Hartree-Fock study that incorporates the effects of Landau-level mixing and screening due to filled levels into the computation of energies and states of quasiparticles in quantum Hall ferromagnets. We use it to construct a phase diagram for skyrmion stability as a function of magnetic field and Zeeman coupling strengths. We find that Landau-level mixing tends to favor spin-polarized quasiparticles, while finite-thickness corrections favor skyrmions. Our studies show that skyrmion stability in high Landau levels is very sensitive to the way in which electron-electron interactions are modified by finite thickness, and indicate that it is crucial to use models with realistic short-distance behavior to obtain qualitatively correct results. We find that recent experimental evidence of skyrmions in higher Landau levels cannot be explained within our model.