SPONTANEOUS INTERLAYER COHERENCE IN DOUBLE-LAYER QUANTUM HALL SYSTEMS- SYMMETRY-BREAKING INTERACTIONS, INPLANE FIELDS, AND PHASE SOLITONS

At strong magnetic fields double-layer two-dimensional-electron-gas sy stems can form an unusual broken symmetry state with spontaneous inter layer phase coherence. The system can be mapped to an equivalent syste m of pseudospin 1/2 particles with pseudospin-dependent interactions a nd easy-plane magnetic order. In this paper we discuss how the presenc e of a weak interlayer tunneling term alters the properties of double- layer systems when the broken symmetry is present. We use the energy f unctional and equations of motion derived earlier to evaluate the zero -temperature response functions of the double-layer system and use our results to discuss analogies between this system and Josephson-couple d superconducting films. We also present a qualitative picture of the low-energy charged excitations of this system. We show that parallel f ields induce a highly collective phase transition to an incommensurate state with broken translational symmetry.