Spin-density wave dynamics in the organic conductor (TMTSF)2X

We have measured current-voltage characteristic in the SDW phase of slightly pressurized (TMTSF)2AsF6 in order to investigate SDW dynamics. Using (TMTSF)2AsF6 crystals with various thickness the threshold electric field (ET) for the SDW depinning was determined. In thick samples, ET depends strongly on temperature above 8K and also below 3K. On the other hand, ET in thinner samples is temperature independent and is approximately 100 mV/cm. It is found that ET at 4.2K increases with decreasing the cross-sectional area (S) when S-4 cm2. Similar phenomenon has been reported in charge-density wave systems. In thin samples, the pinning mechanism seems to be different from that for thicker ones. Sliding properties might be also different between thin and thick samples. From measurements of transient voltage oscillations and excess current density, the pinning periodicity in the thinnest sample was found to be about 8 angstroms. The periodicity which is 4 times larger in thicker ones is almost the same as that expected in the washboard model. It is likely that the whole SDW slides collectively in thinner samples. The effect of the cross-sectional area for SDW dynamics is discussed.