Current-induced voltage noise at zero field in thick and thin films of a-MoxSi1-x

We have performed current-voltage (I-V) and current-induced voltage noise S -V measurements of thick (100 nm) and thin (6 nm) films of amorphous MoxSi1 -x to study vortex dynamics in zero field (B = 0) below the transition temp erature T-c. It is commonly observed that (i) the large 1/f-type noise appe ars in the low current region where the I-V characteristics show strong non linearity; (ii) with increasing I at fixed T, S-V/V (at low frequency f) de creases; and (iii) by applying small B or with increasing T, S-V/V decrease s drastically. These results are consistent with the view that large noise at B = 0 is due to density fluctuations of thermally excited and subsequent ly grown vortex loops and dissociated vortex-antivortex pairs for thick and thin films, respectively. At high I the spectral shape of the thick film. differs from that of the thin film. For the thick film the presence of the long characteristic time has been suggested. (C) 2001 Elsevier Science B.V. All rights reserved.