Static electric dipole polarizabilities of alkali clusters

We have measured the static dipole polarizability of lithium and sodium clu sters (n = 1 - 22). Values measured for sodium are in agreement with previo us experiments. While the polarizability per atom for sodium clusters decre ases slowly as a function of the cluster size, a sharp decrease between siz es 1 and 4 is observed for lithium clusters. Experimental values are compar ed to Density Functional Theory (DFT/PWS1) calculations. The size evolution s for sodium and lithium cluster polarizabilities are well reproduced by ou r calculations. The sharp decrease observed for small lithium clusters is d iscussed in terms of electronic density.