EFFECT OF IMPURITIES ON THE LOW-TEMPERATURE NONLINEAR SPIN-DENSITY-WAVE TRANSPORT

We have measured the low-temperature nonlinear conductivity in the spi n-density-wave state of (TMTSF)(2)X alloys. We find that an expression of sigma(E) = sigma(0E)exp(-E(0)/E), suggestive of a tunneling proces s, describes the nonlinear conduction with the characteristic field E( 0) increasing with increasing disorder while sigma(0E) is independent of the impurity concentration within experimental error. We also discu ss the implications of our findings.