Numerical evidence of diffraction in electronic transmission through a stepped quantum wire

We show a new phenomenon which has been found numerically for coherent electronic transmission through a mesoscopic quantum wire with a step structure. The motion of free electrons in the wire is ballistic with specular reflections from the Dirichlet boundaries. The wire allows only a few modes for electronic transmission. We have found numerically that the electric current shows periodic oscillations with small but nonnegligible amplitudes as a function of a system parameter. We explain that this is purely the effects of diffraction and constructive interference of transmitting electrons at the step structure of the wire.