dc transport in perturbed multichannel quantum wires

We investigate the influence of local defects on the dc transport in mesoscopic quantum wires of finite width. Using the Anderson Hamiltonian for the description of the wires, we solve the Schrödinger equation for scattering boundary conditions. The conductance is then calculated within the Landauer approach. We present a detailed study of the defect-induced fluctuations in the conductance spectra, which are of the order of e²/h. These fluctuations can be related with Fano resonances in the electron transmission spectra, which are due to the coupling between localized defect states and the propagating states of the perfect waveguide. Different kinds of defects are investigated. The case of the double Anderson chain is treated with particular emphasis, since in spite of its simplicity this system possesses all the characteristic features of more complex systems. Our analytical and numerical results reveal the intimate relation between conduction spectra and localized impurity states and provide a basis for the understanding of conductance spectroscopy experiments in mesoscopic systems. The importance of the interaction between localized states and propagating states is also demonstrated by our results for the local current distribution, which becomes strongly inhomogeneous and even vortexlike for Fermi energies near the Fano resonances.