Electron wave interference in ballistic and quasi-ballistic nanostructures

We have studied electron wave interference effects in wires and dots in ballistic and quasi-ballistic transport regimes, fabricated by using split gate, or wet etching techniques. We observe conductance fluctuations as a function of magnetic field, and we show they arise from the different origin of the scattering source for interference. It is shown experimentally that scatterings occur at the boundaries of the wall in the ballistic sample, while they occur at impurities in quasi-ballistic sample. This difference is clearly demonstrated in the temperature dependence of the fluctuation amplitude and the shape dependent negative magnetoresistance peak due to the weak localization effect. We discuss also the phase breaking time in a ballistic dot, which is very important for the interference.