DIFFRACTION IN THE SEMICLASSICAL DESCRIPTION OF MESOSCOPIC DEVICES

In pseudo-integrable systems, diffractive scattering caused by wedges and impurities can be described within the framework of the Geometric Theory of Diffraction (GDT) in a way similar to the one used in the Pe riodic Orbit Theory of Diffraction (POTD). We derive formulas expressi ng the reflection and transition matrix elements for one and many diff ractive points and apply it for impurity and wedge diffraction. Diffra ction can cause backscattering in situations where usual semiclassical backscattering is absent causing an erodation of ideal conductance st eps. The length of diffractive periodic orbits and diffractive loops c an be detected in the power spectrum of the reflection matrix elements . The tail of the power spectrum shows similar to 1/l(1/2) decay due t o impurity scattering and similar to 1/l(3/2) decay due to wedge scatt ering. We think this is a universal sign of the presence of diffractiv e scattering in pseudo-integrable waveguides. (C) 1997 Elsevier Scienc e Ltd.