Coherent-potential approximation calculations in compositionally disordered quantum wires: density of states

The authors have investigated the influence of different types of disorder on the electronic density of states in compositionally disordered quantum wires, using the tight-binding, coherent-potential approximation (CPA). In order to embed the correlations that are present in any wire structure the single-site CPA condition (t i ') config =0, has been generalized to the matrix equation for a slice (L) of the wire as a scatterer (t L ') config =0. Essentially this approximation is similar to the molecular CPA (MCPA) or the cluster CPA but due to the geometry of the system translational invariance along the effective wire is not broken. Calculations for monolayer wires reveal that the boundary roughness of a wire degrades the ideal quasi-one dimensional density of states in a characteristic way. This degradation is even stronger in the presence of islands. The subband representation reveals that the density of states in each channel is affected by the edge disorder in proportion to the Fermi energy or channel number. By contrast the effect of the presence of islands is independent of the channel number.