Observation of Chiral Surface States in the Integer Quantum Hall Effect

We have made experimental studies of low-temperature, high-magnetic field electronic transport in layered, three-dimensional semiconductor structures. In fields that produce the integer quantum Hall effect for transport parallel to the layers, we find deep minima in the vertical conductance G_zz. Between these quantum Hall states, the size dependence of G_zz indicates that vertical transport is through the bulk. Within quantum Hall states, we find that vertical transport is along the surface of the sample, via a “sheath” of extended surface states. This surface sheath is a novel two-dimensional system that exhibits a metallic conductivity ≪e²/h.