Phase transition and non-Ohmic electrical transport in the spin-density-wave state of the organic conductor tetramethyltetraselenafulvalinium hexafluorophosphate [(TMTSF)2PF6]

We report the electric field dependent conductivity in the spin-density-wave (SDW) state of the organic conductor (TMTSF)2PF6 using two different methods for making contacts. A new clamped-contact method reveals that the onset of the SDW transition of (TMTSF)2PF6 may be first order when the sample is strain free. A non-Ohmic behavior of the conductivity is observed above a threshold field in the range of 15 mV/cm. The temperature dependence of the threshold field agrees with a pinning mechanism due to commensurability between the SDW and the underlying lattice. The use of classical painted contacts leads to a smearing of the originally sharp transition and modifies the temperature dependence of the threshold field.