By using an electrochemical gating technique with a new combination of polymer and electrolyte, we were able to inject surface charge densities $n_{2\mathrm{D}}$ as high as $3.5\times {10}^{15}e/{\mathrm{cm}}^2$ in gold films and to observe large relative variations in the film resistance, $\Delta R/R^{\prime }$, up to $10\%$ at low temperature. $\Delta R/R^{\prime }$ is a linear function of $n_{2\mathrm{D}}$—as expected within a free-electron model—if the film is thick enough ($\ge 25\mathrm{nm}$); 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.

• Received 15 August 2011

DOI:https://doi.org/10.1103/PhysRevLett.108.066807