Transition between compressible and incompressible states in infinite-layer fractional quantum Hall systems

Possible phase transitions between incompressible quantum Hall states and compressible three-dimensional states are discussed for infinite-layer electron systems in strong magnetic field. By variational Monte Carlo calculation, relative stability of some trial states is studied. If the interlayer distance is large enough, the Laughlin state is stabilized for the Landau level filling $\nu =1/3\mathrm{}$ of each layer. When the interlayer distance is comparable to the magnetic length, the Laughlin state becomes unstable against a different fractional quantum Hall state with interlayer correlation, and/or against a three-dimensional compressible state. It is discussed how the quantum phase transition between them can be controlled in actual systems.