Superconductor-insulator transition with non-universal conductivity
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Motivated by experimental evidence for the importance of fermionic degrees of freedom near the superconductor-insulator transition, we take into account gapless electronic excitations for the description of the transition. Integrating them out yields a damping for the phase of the superconducting grains. We derive a Ginzburg-Landau-Wilson description for the onset of superfluidity which shows a non-ohmic dynamics. This dynamics depends qualitatively on the strength of the damping. Sufficiently strong damping modifies both, the critical behavior and the response near the transition. The critical exponents depend on the damping strength. The conductivity at the transition is finite but non-universal.