Engineering Superconductivity by Molecular Charge Transfer

By mixing donor and acceptor molecular systems, different classes of materials such as insulators, metals, semiconductors and superconductors can be formed. Here we engineer nanoscale superconducting clusters by depositing donor BETS and acceptor GaCl$_{4}$ on a Ag(111) surface. First, we probe the electronic properties of individual species, BETS and Et4N-GaCl$_{4}$ on Ag(111) using tunneling spectroscopy at 5.4 K. Based on strong molecule-molecule interactions, both molecular species form clusters on the surface, and the corresponding tunneling spectroscopy data do not reveal any features around the Fermi level. A surprising structural transformation occurs when both molecular species are put together on this surface where the BETS start forming long chains. Tunneling spectroscopy data of the molecular clusters with mixed species shows formation of new HOMO-LUMO level. Most astoundingly, high resolution spectroscopy data reveal the existence of the superconducting gap within these clusters, thus opening a novel avenue of molecular superconductivity at the nanoscale spatial limit.