The pair-fluctuation contribution reduces the electrostatic screening length in superconductivity as compared to the normal state. When a conductor possesses a static background charge distribution, superconductivity arises even in the absence of an explicit pairing interaction, such that the Coulomb repulsion is reduced and the total energy is lowered. We demonstrate that the superconducting gap increases with increased background charge at first, after which the mixing of the Higgs and plasma modes suppresses superconductivity in the pseudogap phase. This indicates that the mechanism may be relevant to the cuprates and iron pnictides. When the background charge is identified with the incoherent component of optical conductivity in the cuprates, our results reproduce the shape, size and position of the superconducting dome with zero free parameters. A superconducting critical temperature of about 1000 K is possible in ion-doped conductors.
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