By using an electrochemical gating technique with a new combination of polymer and electrolyte, we were able to inject surface charge densities n2D as high as 3.5\ifmmode\times\else\texttimes\fi{}1015\,\,e/cm2 in gold films and to observe large relative variations in the film resistance, $\Delta${}R/R$'${}, up to 10% at low temperature. $\Delta${}R/R$'${} is a linear function of n2D\char22{}as expected within a free-electron model\char22{}if the film is thick enough ($\ge${}25\,\,nm); otherwise, a tendency to saturation due to size effects is observed. The application of this technique to 2D materials might allow extending the field-effect experiments to a range of charge doping where large conductance modulations and, in some cases, even the occurrence of superconductivity are expected.

In the last 60 years conventional solid and electrolyte gating has allowed sizable modulations of the surface carrier concentration in metallic superconductors, resulting in tuning of their conductivity and change of their critical temperature. Recent conventional gating experiments on superconducting metal nanostructures showed full suppression of the critical current without variation of the normal-state resistance and the critical temperature. These results still lack a microscopic explanation. In this article, we describe a complete set of gating experiments on $\mathrm{Ti}$-based superconducting Dayem-bridges and a proposed classical thermodynamic model that seems to account for several of our experimental findings. In particular, zero-bias resistance and critical-current $I_C$ measurements highlight the following: the suppression of $I_C$ with both polarities of gate voltage, the surface nature of the effect, the independence of critical temperature from the electric field, and the gate-induced growth of a subgap dissipative component. In addition, the temperature dependence of the Josephson critical current seems to show a transition from ballistic Kulik-Omelyanchuk behavior to Ambegaokar-Baratoff tunnellike behavior on increase of the electric field. Furthermore, the $I_C$ suppression persists in the presence of sizable perpendicular-to-plane magnetic fields. We propose a classical thermodynamic model able to describe some of the experimental observations of the present and previous work. Above all, the model grabs the bipolar-electric-field-induced suppression of $I_C$ and the emergence of a subgap dissipative component near full suppression of the supercurrent. Finally, applications using the effect discussed are proposed.