TRANSITION FROM CHAOTIC TO REGULAR QUANTUM SCATTERING IN MESOSCOPIC BILLIARDS WITH NOMINALLY REGULAR GEOMETRY

We discuss the origin of a striking transition in the weak localisatio n lineshape observed in the low temperature magneto-resistance of ball istic quantum dots with square geometry. As the dot openings are gradu ally closed, the lineshape evolves from a Lorentzian to a linear form and. within the framework of the present theory, this behaviour can on ly be explained in terms of a corresponding transition from chaotic to regular behaviour within the devices. In order to determine the origi n of this transition, we have performed classical simulations of balli stic transport within such dots, taking in to account the nature of th e self-consistent potential. Poincare sections for the motion then ind eed reveal a transition from chaotic to regular behaviour as the leads are pinched off, which appears to be associated with increasing colli mation of the incoming electron beam.