Lead-induced transition to chaos in ballistic mesoscopic billiards

We show a striking transition in the line shape of the weak localization peak, observed in the low-temperature magnetoresistance of square semiconductor billiards. More specifically, as the point-contact openings to the dots are closed, the line shape is found to develop a non-Lorentzian dependence. In the smaller dot studied, this can be clearly described as a transition to a linear peak, and within the framework of current theory this behavior can only be explained in terms of a transition, from chaotic to regular scattering in the dot. Appealing to the results of self-consistent potential-profile calculations, we argue that this occurs as the leads of the dot are closed, and the resulting geometry becomes more closely approximated as a square. Our results therefore demonstrate that the lead openings of real conductors exert an important bearing on the resulting electron scattering, which must be taken into account to achieve a satisfactory description of transport.