REENTRANT LOCALIZATION AND A MOBILITY GAP IN SUPERLATTICE MINIBANDS

We develop a theory of the mobility edge for transport in superlattice minibands. For small W, where 2W is the bandwidth, the mobility edge Ec diverges as ln1/W, so that all states are localized in the limit W0. For large values of Wwe find Ec1/W, and the system behaves as an anisotropic conductor. For intermediate values of W, the system can develop a mobility gapa band of localized statesat the Van Hove singularity in the density of states. This reentrant localization behavior should be experimentally observable and may explain some recent experimental results. © 1990 The American Physical Society.