Neutral superfluid modes and ‘‘magnetic’’ monopoles in multilayered quantum Hall systems

We show that, in the absence of interlayer hopping, the ν=1/m quantum Hall states in double-layer systems contain a neutral gapless mode with linear dispersion, describing the relative fluctuations of the electron densities in the two layers. At finite temperature the system experiences a Kosterlitz-Thouless transition. In the presence of interlayer hopping an energy gap proportional to the square root of the hopping amplitude will be opened. In field theory this corresponds to a U(1) gauge field acquiring a mass due to the monopole-antimonopole plasma in the (2+1)-dimensional spacetime.