Nearly constant loss spectra in glasses: Dipolar interaction effects

The relaxation properties of dynamical probes in random dipolar systems exhibit pronounced non-Debye features even at moderate temperatures. These non-Debye features have their origin in broad Levy type local field distributions and strong correlations in the collective dynamics of nearby dipoles. We discuss two examples of experimental relevance: The dephasing and decay of polarization of an ensemble of spin-polarized particles brought into a random assembly of superparamagnetic clusters, and the nearly constant loss behavior widely observed in the dielectric response of disordered materials.