Transition from laminar to vortical current flow in electron waveguides with circular bends

We have analyzed the spatial flow pattern in two-dimensional ballistic electron waveguides with circular bends. For a double bend the conductance may still be perfectly quantized in spite of the strong mixing of modes. In narrow energy regions just below the subband thresholds there is strong interference between localized and propagating solutions, causing an interference blockade. Within these regions the current flow becomes vortical. Minor changes in, e.g., energy cause drastic changes in the flow pattern.