SIZE-EFFECT OF KONDO SCATTERING BY FE IMPURITIES IN CU POINT CONTACTS

The low temperature dV/dI(V) characteristics are investigated for poin t contacts of various sizes (d approximate to 2-35 nm) using a mechani cally controlled breakjunction of a Kondo alloy CuFe (0.1 at. %), a si ze effect, being manifested in an increase in the effective Kondo temp erature with decreasing contact size, is found both on voltage and mag netic field dV/dI dependences. In accordance with the prediction of th e Zarand-Udvardi theory the enhancement of the Kondo temperature in th e CuFe alloy appears to be quantitatively much smaller than in CuMn al loy of the same concentration. This enhancement is due to the strong f luctuations of the local electron density of states in the ultrasmall metallic contacts. The Kondo temperature of a magnetic impurity provid es a local probe of these fluctuations.