Surface anisotropy and the Kondo effect in restricted geometry (invited)

In recent years, several groups have demonstrated experimentally that in th in films the Kondo effect has a smaller amplitude but roughly the same Kond o temperature compared to the bulk values. We have developed a theory of su rface anisotropy proportional to KdSz2, where S-z is the component of the i mpurity spin perpendicular to the surface and K-d is an amplitude which is proportional to the inverse of the distance measured from the surface. The anisotropy is due to the fact that conduction electrons interact not only w ith the magnetic impurity by the exchange interaction, but also with the ho st atoms by the spin-orbit interaction, which allows the impurity spin to g et information about the shape of the sample. Near the surface of the sampl e and at low temperature, the spin degrees of freedom freeze in the singlet ground state for spin S=2 so that the impurities at the surface cannot con tribute to the Kondo anomaly, in contrast to the case S=5/2 where the groun d state is degenerate. The theory of the surface anisotropy is in good agre ement with experiments examining Kondo resistivity and magnetoresistance in the ballistic regime, while in the dirty limit, a different theory is requ ired, which has recently been developed by I. Martin, Y. Wan, and P. Philli ps. (C) 2000 American Institute of Physics. [S0021-8979(00)93408-X].