Kondo tunneling through real and artificial molecules

When a cerocene molecule is chemisorbed on metallic substrate, or when an asymmetric double dot is hybridized with itinerant electrons, its singlet ground state crosses its lowly excited triplet state, leading to a competition between the Zhang-Rice mechanism of singlet-triplet splitting in a confined cluster and the Kondo effect (which accompanies the tunneling through quantum dot under a Coulomb blockade restriction). The rich physics of an underscreened S=1 Kondo impurity in the presence of low-lying triplet/singlet excitations is exposed. Estimates of the magnetic susceptibility and the electric conductance are presented.