TRANSITION FROM STRONG TO WEAK ELECTRON LOCALIZATION IN A PERCOLATINGGOLD FILM UNDER THE INFLUENCE OF AN ELECTRIC-FIELD

The low-temperature (0.5-55 K) conductivity of a semicontinuous gold f ilm near the percolation threshold is studied. It is found that the hi m resistance is very sensitive to the applied voltage U. By varying U, the him can be reversibly transformed from the insulating to the meta llic type conductivity. This makes it possible to study the metal-insu lator transition (MIT) by tuning the electric field. For low U less th an or equal to 0.05 V, the film behaves as an insulator with the sheet resistance R-square up to 10 M Omega. In this state, the dependences R(T)(proportional to)exp(1/T) (for T less than or equal to 20 K) and R (U)(proportional to)exp(1/U) (for T less than or equal to 1 K and U>0. 1 V) are observed. At high voltages (U similar or equal to 10 V), the film has the resistance R(square)similar or equal to 5 k Omega and beh aves like a ''dirty'' metal. The magnetoresistance (MR) in the metalli c state is positive and corresponds to the weak localization effect. I n the insulating state, the MR is negative and is described by the for mula Delta R(H)/R(0)(proportional to)-H-2/T. The negative MR manifests itself for nearest-neighbor hopping. Such behavior is unusual, and it s nature is unclear. The dependences of resistance on temperature, vol tage, and magnetic field as well as the general nature of the observed MIT are considered on the basis of the obtained results. (C) 1997 Ame rican Institute of Physics.