Topological Excitations in Double-Layer Quantum Hall systems

Double layer quantum Hall systems with spontaneous broken symmetry can exhibit a novel manybody quantum Hall effect due to interlayer coherence. When layer separation becomes large and close to the critical one, quantum fluctuations destroy interlayer coherence and accordingly quantum Hall effect collapses. We calculate the renormalized isospin stiffness $\rho_s^R$ due to quantum fluctuations within Hartree-Fock-RPA formalism. The activation energy of the topological excitations thus obtained demonstrates a nice qualitative agreement with recent experiment.