Quantized Hall Effect and zero resistance state in a three- dimensional electron system.

Quantization of the Hall effect and vanishing diagonal resistivity is observed in a GaAs-(A1Ga)As superlattice which, in the absence of a magnetic field, conducts in all three spatial dimensions. In the quantized state, the conductivity parallel to the magnetic field tends toward zero. These findings suggest that rather than two-dimensionality of the electronic system, it is the absence of conductivity along the magnetic field which is a necessary condition for the observation of the quantized Hall effect.