Global and local level dynamics in chaotic microwave billiards

The spectra of Sinai microwave billiards and rectangular billiards with statistically distributed circular scatterers have been taken as a function of the position of one wall, and of one of the scatterers, respectively. Whereas in the first case the velocity distribution and correlations obey the universal behaviour predicted by Simons and Altshuler, in the second case a completely different behaviour is observed. This is due to the fact that a shift of one wall changes the wave function globally whereas the displacement of one scatterer only leads to a local perturbance.