NUCLEAR SPINS AS PROBES FOR CONDUCTION ELECTRONS

Due to the short correlation time of conduction electrons at the nuclear sites the ensemble averages of the hyperfine interaction are observed. The nuclear magnetic resonance frequency is shifted by the polarization of the electrons (Knight shift) and the electron spin resonance frequency is shifted by the polarization of the nuclei (Overhauser shift). Both shifts allow to use nuclei as local probes for conduction electrons. In systems with low conduction electron densities, the Knight shift is very small, whereas the Overhauser shift is independent of the electron density. In these systems the Overhauser shift technique is a sensitive tool, since it can be combined with methods of dynamic nuclear polarization. Applications of this technique to conduction electron systems with different dimensions (3D, 2D, 1D) are reported.