▎ 摘　　要

At half-filling of the fourfold degenerate Landau levels vertical bar n vertical bar >= 1 in graphene, the ground states are spin-polarized quantum Hall states that support spin skyrmion excitations for vertical bar n vertical bar = 1,2,3. Working in the Hartree-Fock approximation, we compute the excitation energy of an unbound spin skyrmion-antiskyrmion excitation as a function of the Zeeman coupling strength for these Landau levels. We find for both the bare and screened Coulomb interactions that the spin skyrmion-antiskyrmion excitation energy is lower than the excitation energy of an unbound spin-1/2 electron-hole pair in a finite range of Zeeman coupling in Landau levels vertical bar n vertical bar = 1,2,3. This range decreases rapidly for increasing Landau level index and is extremely small for vertical bar n vertical bar = 3. For valley skyrmions, which should be present at 1/4 and 3/4 fillings of the Landau levels vertical bar n vertical bar = 1,2,3, we show that screening corrections are more important in the latter case. It follows that an unbound valley skyrmion-antiskyrmion excitation has lower energy at 3/4 filling than at 1/4. We compare our results with recent experiments on spin and valley skyrmion excitations in graphene.