The role of lead openings in regular mesoscopic billiards

We discuss the results of experimental studies of ballistic electron transport in regular (i.e. non-chaotic) quantum dots. At low temperatures, coherent interference between electrons gives rise to reproducible fluctuations in the magneto-resistance, as well as to a weak localization peak near zero field. The lineshape of the peak evolves from a Lorentzian to a linear form, as the leads of the dot are closed, while the fluctuations exhibit striking quasi-periodicity, suggesting that transport through regular dots is dominated by just a small group of trajectories. Simulations show that these characteristics in turn result from the ability of the quantum point contact leads, to strongly select which trajectories participate in transport.