Tunneling measurements of fluctuation effects near the superconductor to insulator transition

We present measurements of the temperature dependence of the tunneling density of states near the Fermi energy, G₀(T), and resistive transitions, R(T), of ultrathin PbBi films. Both R(T) and G₀(T) broaden substantially near the superconductor to insulator transition (SIT). The broadening in R(T) is not affected by the proximity of a ground plane suggesting that long range Coulomb interactions are not important to the SIT. The results suggest that the transport properties of films near the SIT are influenced by fluctuations in both the phase and the amplitude of the order parameter. We discuss the data in terms of recent theories of the superconducting transition in low superfluid density systems.