Metastable Conduction States in Mo\u3csub\u3e2\u3c/sub\u3eS\u3csub\u3e3\u3c/sub\u3e: Conductivity Fluctuations

In this paper, we present the results of measurements of the frequency and temperature dependences of the electrical noise in Mo2S3. It will be seen that the frequency dependence of the noise is completely consistent with the double-well potential model for the carriers in Mo2S3 introduced in an earlier paper [Phys. Rev. B 38, 3973 (1988)]. In the earlier paper, we showed that at temperatures below 145 K, the carriers in Mo2S3 could exist in either a weakly conducting ground state or a relatively highly conducting metastable state. The conductivity behavior of Mo2S3 was found to be consistent with a phenomenological double-well potential model in which the ground state is separated from the metastable state by a large energy barrier of height W. The model predicts that carriers transfer from one state to the other by thermal activation, so that the lifetime of the carriers in the metastable state varies strongly with temperature according to τ= τ0exp (W/kT), with W=0.25 eV and τ0=5X10-15 sec. The magnitude of the electrical noise measurements reported here, when coupled with the magnitude of the conductivity and the carrier density, require either that the carriers in Mo2S3 have a very large mobility (~4X104 cm2/Vs), or that the carriers behave cooperatively, as they would if Mo2S3 were a charge-density-wave system