SHAPE-AVERAGED WEAK-LOCALIZATION IN CHAOTIC AND INTEGRABLE BALLISTIC CAVITIES

We perform magnetotransport measurements in ballistic cavities and obt ained the average by small modulations on the shapes and/or on the Fer mi level. We work with cavities whose underlying classical dynamics is chaotic (stadia and stomachs) and integrable (circles and rectangles) . The former show a Lorentzian weak-localization peak, in agreement wi th semiclassical predictions and other averaging methods that have bee n used in recent measurements. For integrable cavities our measurement s are in disagreement with the existing experimental results. These di screpancies illustrate the non-generic behaviour of scattering through integrable geometries that we analyse taking into account the interpl ay of integrability with smooth disorder and geometrical effects. The power spectra of the conductance fluctuations are also analysed, the d educed typical areas are in good agreement with those obtained from th e weak localisation. The presence of periodic orbits in non-averaged F ourier transforms of the magnetoconductance for regular cavities indic ates the good quality of our samples. (C) 1997 Elsevier Science Ltd.