SIMULATIONS OF FLUCTUATIONS IN QUANTUM-WIRE MESOSCOPIC SYSTEMS

We examine the geometry dependence of the conductance fluctuations in a quantum wire, using the recursive Green's function technique, by changing the width of a wire with fixed length. In the experimental situation, the quantum wire is 'connected' to 'wide' and 'long' disordered contact regions which are often ignored in calculations. This more complicated quantum wire geometry lends itself to a numerical approach but would be very difficult to tackle from the viewpoint of the diagrammatic perturbation theory. We can include these disordered contact regions easily in our calculations: and our numerical results suggest that the presence of these contacts tends to reduce the fluctuations. This is a consequence of entering the transport 'localization regime', where the sample length is of the order of the localization length, for the longer structure with the disordered contacts.