Evolution of the ESR spectrum at the metal-insulator transition in quasi-one-dimensional systems

The evolution of ESR spectra in metals containing both conduction electrons and localized paramagnetic centers with inhomogeneous broadening of the magnetic resonance is treated theoretically. It is shown that such a spectrum can be effectively narrowed when a relaxation bottleneck is present for an arbitrary distribution of inhomogeneous broadening. The temperature dependence of the ESR spectrum in the polymeric phase of RbC60 is investigated experimentally in the region of the metal-insulator transition. Application of the calculations to the experimental data demonstrates good agreement with the physical model if it is assumed that the given material is a quasi-one-dimensional system.