Bag Formation in Quantum Hall Ferromagnets

Charged skyrmions or spin–textures in the quantum Hall ferromagnet at filling factor ν = 1 are reinvestigated using the Hartree–Fock method in the lowest Landau level approximation. It is shown that the single Slater determinant with the minimum energy in the unit charge sector is always of the hedgehog form. It is observed that the magnetization vector’s length deviates locally from unity, i.e. a bag is formed which accommodates the excess charge. In terms of a gradient expansion for extended spin–textures a novel O(3) type of effective action is presented, which takes bag formation into account. PACS 73.40.Hm, 73.20.Dx, 12.39.Dc