ON THE LOW-TEMPERATURE DEPENDENCE OF THE THRESHOLD FIELD OF CDW IN NBSE3 - EFFECT OF UNIAXIAL-STRESS

We investigated the effect of uniaxial stress on the threshold field i n NbSe3. For the upper CDW, we show a clear separation of the threshol d field into two additive components, E(T)'(t) and E(T)''(t, epsilon) where t = T/T p, The impurity dependence of E(T)''(t, epsilon) indicat es that this term is the impurity or bulk pinning term. E(T)''(t, epsi lon) shows strong temperature dependence near T(p) but saturates to a t independent minimum below t almost-equal-to 85. On the other hand, t he term E(T)'(t) takes nearly all the temperature dependence of the E( T) below t(min); it varies as E0 exp[-t/t0]. Comparison with contact e ffect and size effect data by other researchers indicates that E0 is v ery sensitive to size effects while t0 is independent of sample size a nd of impurity content as well. We argue that the temperature dependen ce of E(T) is well described by the equation E(T)(T) = E(FLR) + E0exp( T/T0) with T0 = 16 K for the upper CDW.