Size effects on superconductivity and Kondo behavior in CeCo2

Size effects on superconductivity and Kondo behavior were studied on a series of CeCo$_{2}$ nanoparticles (5.8-24 nm) by heat capacity measurements at T=0.4-30 K and H=0-8 T. In contrast to bulk CeCo$_{2}$ superconductor ($T_{C}\sim $1.3 K), no superconductivity instead an enhancement of Kondo anomaly with $T_{K }$= 1.6-8.8 K was revealed. Anderson's criterion can't explain the results, especially for $d \quad \ge $ 11 nm. To answer the problem the competition between Kondo interactions and superconductivity was proposed. In addition, the size dependence of $T_{K}$ and its correlation with lattice constant were observed.