QUANTUM DYNAMICAL ECHOES IN THE SPIN-DIFFUSION IN MESOSCOPIC SYSTEMS

The evolution of local spin polarization in finite systems involves in terference phenomena that give rise to quantum dynamical echoes and no nergodic behavior. We predict the conditions to observe these echoes b y exploiting the NMR sequences devised by Zhang er al. [Phys. Rev. Let t. 69, 2149 (1992)], which uses a rare C-13 as the local probe for a d ipolar coupled H-1 spin system. The nonideality of this probe when tes ting mesoscopic systems is carefully analyzed revealing the origin of various striking experimental features.