We study localization in layered, three-dimensional conductors in strong magnetic fields. We demonstrate the existence of three phases—insulator, metal, and quantized Hall conductor—in the two-dimensional parameter space obtained by varying the Fermi energy and the interlayer coupling strength. Transport in the quantized Hall conductor occurs via extended surface states. These surface states constitute a subsystem at a novel critical point, which we describe using a new, directed network model.

• Received 6 July 1995

DOI:https://doi.org/10.1103/PhysRevLett.75.4496