On the low temperature dependence of the threshold field of CDW in NbSe₃ : effect of uniaxial stress

Abstract
We investigated the effect of uniaxial stress on the threshold field in NbSe₃. For the upper CDW, we show a clear separation of the threshold field into two additive components, E'_T(t) and E"_T(t,ε) where t = T /Tp. The impurity dependence of E"_T(t,ε) indicates that this term is the impurity or bulk pinning term. E"_T(t,ε) shows strong temperature dependence near T_p but saturates to a t independent minimum below t ≈ 0.85. On the other hand, the term E'_T(t) takes nearly all the temperature dependence of the E_T below t_Min ; it varies as E_o exp(-t/t0). Comparison with contact effect and size effect data by other researchers indicates that E_o is very sensitive to size effects while t_o is independent of sample size and of impurity content as well. We argue that the temperature dependence of E_T is well described by the equation E_T(t) = E_FLR + E_oexp(T/T_o) with T_o = 16 K for the upper CDW.