Magnetic impurity effect on superconductivity and Kondo temperature in ultrathin Pb films with adsorbed 3d transition metal atoms

Suppression of the superconducting transition temperature by magnetic adatoms is studied for a-few-atomiclayer-thick Pb films grown on a cleaved GaAs(110) surface. The normalized suppression rate eta varies greatly with the spin S of the adatom. Furthermore, we find that eta is strongly enhanced by a coating with Au or Ag on the Pb film. On the basis of calculations using the Matsuura, Ichinose, and Nagaoka theory of the Kondo effect in superconductors, the results are explained by a strong negative S dependence of the Kondo temperature TK and a reduction of TK due to the coating.