Electrostatic tuning of the superconductor-insulator transition in two dimensions.

Superconductivity has been induced in insulating ultrathin films of amorphous bismuth using the electric field effect. The screening of the electron-electron interaction was found to increase with electron concentration in a manner correlated with the tendency towards superconductivity. This does not preclude an increase in the density of states being important in the development of superconductivity. The superconductor-insulator transition appears to belong to the universality class of the three dimensional XY model.