Josephson Coupled Quantum Dot Artificial Solids

Josephson coupled quantum dot artificial solids were prepared from 20 ± 4 nm diameter organically functionalized Pb particles. Interparticle separation distances were varied from approximately 26 to 11 Å by varying the passivating organic ligand. Isolated particles were too small to exhibit a Meisner effect by themselves, and so it was possible to employ SQUID magnetometry as a zero-background probe for Cooper pair delocalization in these solids. As the interparticle separation distance was decreased, the quantum dot solids progressed from a Mott insulator to a strongly localized superfluid, and finally to a superfluid.