Superconducting transition of FeSe / SrTi O3 induced by adsorption of semiconducting organic molecules

We prepared superconducting and nonsuperconducting FeSe films on SrTiO3(001) substrates (FeSe/STO) and investigated the superconducting transition induced by charge transfer between organic molecules and FeSe layers by low temperature scanning tunneling microscopy and spectroscopy. At low coverage, donor- and acceptor-type molecules adsorbed preferentially on the nonsuperconducting and superconducting FeSe layers, respectively. Superconductivity was induced by donor molecules on nonsuperconducting FeSe layer, while the superconductivity was suppressed near acceptor molecules. The corresponding evolutions of electronic states and work function were also resolved by scanning tunneling microscopy. These results illustrate the important role played by local electron concentration in the superconducting transition of FeSe/STO.