Bag formation in quantum Hall ferromagnets

Charged skyrmions or spin textures in the quantum Hall ferromagnet at a filling factor ν=1 are reinvestigated using the Hartree-Fock method in the lowest-Landau-level approximation. It is shown that a single Slater determinant with 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, an O(3) type of effective action is presented, which takes bag formation into account.