Activation studies of pseudospin quantum Hall ferromagnets in double quantum wells

We study pseudospin quantum Hall ferromagnets realized in a strongly coupled double-quantum-well structure. The pseudospin dependence of the Coulomb interactions leads to magnetic anisotropy. Activation energies measured as a function of the single-particle gap, i.e. the pseudospin Zeeman energy, reveal a striking difference between the easy-axis and easy-plane ferromagnets. In the limit of zero single-particle gap, we observe a novel low-energy excitation, reminiscent of Skyrmions, for the ν=4 easy-axis ferromagnet. We discuss the reduced gap in terms of topological charge excitations in the domain walls.