Kondo effect in systems of reduced dimensionality

This paper describes a series of experiments concerning the Kondo effect in metal films and wires which have revealed some surprising aspects of the Kondo behavior in quasi-two- and quasi-one-dimensional systems. We have studied two different Kondo alloys, Au(Fe) and Cu(Fe), and found that in both cases the Kondo contribution to the resistivity {Δ}ρK is sensitive to the size of the sample, and is suppressed at length scales below about 1500 {}. This critical length scale is observed in both quasi-two- and quasi-one-dimensional systems. Studies of bilayer samples composed of a Kondo film in contact with a layer of the pure host material [e.g., Cu(Fe) overcoated with Cu] reveal the existence of a Kondo proximity effect, which is also length scale dependent. Results for the spin scattering rate τₛ^-1 for conduction electrons, obtained via weak localization measurements, indicate that τₛ^-1 is suppressed in quasi-two-dimensional systems in a manner similar to that found for {Δ}ρK. Finally, we find that disorder plays a central role; increasing the amount of disorder (i.e., elastic scattering) suppresses {Δ}ρK. Surprisingly, the length scale which controls the Kondo behavior seems to be essentially independent of the Kondo temperature TK. This implies that physics beyond that contained in the simplest Kondo models is responsible.