  As it is well known most of charge density wave (CDW) and spin density wave
(SDW) exhibit the nonlinear transport with well defined threshold electric
field E_T. Here we study theoretically the threshold electric field of
unconventional density waves. We find that the threshold field increases
monotonically with temperature without divergent behaviour at T_c, unlike the
one in conventional CDW. The present result in the 3D weak pinning limit
appears to describe rather well the threshold electric field observed recently
in the low-temperature phase (LTP) of alpha-(BEDT-TTF)_2KHg(SCN)_4.
