Nonlinear conduction in the spin-density-wave ground state

We have investigated the effect of hydrostatic pressure and magnetic field on the nonlinear electrical conduction in (TMTSF${)}_{2}$${\mathrm{PF}}_{6}$ at T=350 mK. The observed variations are described in terms of a tunneling expression, where the influence of pressure and of magnetic field can be separated. We establish the relation between the current density and the spin-density-wave order parameter and discuss the origin of possible tunneling barriers.