TOPOLOGICAL EXCITATIONS IN DOUBLE-LAYER QUANTUM-HALL-SYSTEMS

Double-layer quantum Hall systems with spontaneous broken symmetry can exhibit a novel many body quantum Hall effect due to the strong inter layer coherence. When the layer separation becomes close to the critic al value, quantum fluctuations can destroy the interlayer coherence an d the quantum Hall effect will disappear. We calculate the renormalize d isospin stiffness rho(s) due to quantum fluctuations within the Hart ree-Fock-RPA formalism. The activation energy of the topological excit ations thus obtained demonstrates a nice qualitative agreement with re cent experiment.