1 F NOISE IN NONLINEAR INHOMOGENEOUS SYSTEMS

1/f noise has been measured in detail in a composite system of carbon- wax mixtures using a range of bias (V) that covered both linear and no nlinear regimes. S-V-V characteristics have been obtained and exhibit structures that can be correlated to those of conductance. It is found that the variation of S either by the conducting fraction or V is des cribed by the same power law, R(omega), but with different exponents 1 .7+/-0.2 and similar to 3, respectively. Here S is the relative noise power and R is the chordal resistance. The noise data are consistent w ith results obtained earlier with I-V or dI/dV measurements. It is sho wn that the data can be explained by the addition of tunneling bonds a s a result of applying voltage. Similar measurements have been carried out for comparison in samples of conducting polymer and V2O4 which fo llow Mott's variable-range hopping conduction and, thus, are different from mixtures. Differences in noise behavior with respect to the comp osites point to the usefulness of extending noise measurements to nonl inear regimes in other physical systems.