Current noise in stationary conditions in MgB2 thin films

The present paper concerns the analysis of the current noise taken in stationary conditions at different stages of the transition process in MgB₂ thin films. The specimen, during its transition, reaches an intermediate state characterized by resistive and superconductive regions. Except in the case where the specimen resistance is lower than about one tenth of its value at the end of the transition, both the amplitude and frequency behavior of the relative noise power spectra remain rigorously constant at different stages of the transition curve, until the transition is completed and the fully normal state is achieved. A different picture appears at the beginning of the transition, where the specimen resistance increases slowly with the temperature, before reaching the steepest part of the transition curve. Contrarily to the previous case, now the specimen reaches a mixed state, and the noise is produced by depinning and motion of fluxoids. Actually the amplitude of the reduced noise power spectrum becomes very sensitive to both to the magnetic field and the specimen resistance, and is largely dominant when this resistance tends to zero.