WHAT IS THE THOULESS ENERGY FOR BALLISTIC SYSTEMS

The Thouless energy E(c) characterizes numerous quantities associated with sensitivity to boundary conditions in diffusive mesoscopic conduc tors. What happens to these quantities if the disorder strength is dec reased and a transition to the ballistic regime takes place? In the pr esent analysis we refute the intuitively plausible assumption that E(c ) loses its meaning as an inverse diffusion time through the system at hand and generally disorder independent scales take over. Instead we find that a variety of (thermodynamic) observables are still character ized by the Thouless energy.