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 interlayer coherence. When the layer separation becomes close to the critical value, quantum fluctuations can destroy the interlayer coherence and the quantum Hall effect will disappear. We calculate the renormalized isospin stiffness rho(s) due to quantum fluctuations within the Hartree-Fock-RPA formalism. The activation energy of the topological excitations thus obtained demonstrates a nice qualitative agreement with recent experiment.