Fluctuation conductivity of granular vanadium films

The effect of fluctuations on the resistive transitions in thin granular vanadium films at temperatures T ≥ Tc is studied. As the temperature is increased and as a result of the change in the ratio of the coherence length ξ(T) and the average size of the granules g, the dimensionality of the fluctuations changes in all films studied from two [ξ (T) >g] to zero [ξ (T) >g] .Studies of the region of the two-dimensional behavior of the fluctuations showed that the Maki–Thompson mechanism makes the main contribution to the fluctuation conductivity σ′ of such films. The study of critical fluctuations showed that the theory describes well both the behavior of σ′ as a function of temperature and the width of the resistive transitions near Tc. The effect of microwave radiation with frequency ∽ 10 GHz and power P on the resistive transitions and σ′ of such films was studied. It was found that a) the dimensionality of the weak fluctuations changes; b) the region of critical fluctuations decreases as a result of stimulation and then expands as P increases; c) superconductivity is stimulated in the zero-dimensional ensemble of small particles near the temperature of their resistive transition. Most of the observed effects can be explained satisfactorily based on the granular nature of the films.

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