Phase transitions in a multiple quantum well in strong magnetic fields

We study the phases of a multiple-quantum-well system of layered two-dimensional electrons in a strong perpendicular magnetic field. Solid phases are found at small fillings of the lowest Landau level which are the hexagonal-close-packed lattice at large interlayer separations and the body-centered-tetragonal lattice at small separations. We find that a sequence of incompressible-Laughlin-liquid-like states occurs at larger fillings. The energies and correlation functions of these states have been calculated by using Monte Carlo simulations. We also discuss the quasiparticle and collective excitations of the liquid states. We find that the electric charge carried by a quasiparticle can have a contribution in one layer which is an irrational fraction of the electron charge. It should be possible to observe the transitions between different Laughlin-like phases experimentally. Transport and microwave experiments are particularly promising in this regard.