Transition from strong to weak electron localization in a percolating gold film under the influence of an electric field

Abstract

The low-temperature (0.5–55 K) conductivity of a semicontinuous gold film near the percolation threshold is studied. It is found that the film resistance is very sensitive to the applied voltage U. By varying U, the film can be reversibly transformed from the insulating to the metallic type conductivity. This makes it possible to study the metal–insulator transition (MIT) by tuning the electric field. For low U⩽0.05 V, the film behaves as an insulator with the sheet resistance R□ up to 10 MΩ. In this state, the dependences R(T)∝exp(1/T) (for T⩽20 K) and R(U)∝exp(1/U) (for T⩽1 K and U>0.1 V) are observed. At high voltages (U≃10 V), the film has the resistance R□≃5 kΩ and behaves like a “dirty” metal. The magnetoresistance (MR) in the metallic state is positive and corresponds to the weak localization effect. In the insulating state, the MR is negative and is described by the formula ΔR(H)/R(0)∝−H2/T. The negative MR manifests itself for nearest-neighbor hopping. Such behavior is unusual, and its nature is unclear. The dependences of resistance on temperature, voltage, and magnetic field as well as the general nature of the observed MIT are considered on the basis of the obtained results.