DYNAMICS AND PHASE TRANSITIONS OF SPIN-DENSITY WAVES

研究了一种典型的有机电荷转移盐(TMTSF)2AsF6的电导率。得到了电导率随压力、温度和电场的变化关系。确定了金属-半金属转变温度和自旋密度波相的热激活能与压力的函数关系。结果表明，金属-半金属相转变与法向自旋密度波相变无关，在相变温度以上，特别是在中压临界压力附近，存在半金属自旋密度波相，得到了自旋密度波滑移引起的非线性电导的阈值电场随温度的变化。将计算结果与Maki等人的理论进行了比较。在3K以上的温度范围内，该系统中的自旋密度波很可能是由与晶格的可公度性而不是杂质所钉扎的。这是Th…的首次发现在贝克加德盐类中有更多的自旋密度波和相称的波矢量。在3K的低压下，阈值电场和非线性电导率的温度依赖关系都发生了变化。结果表明，自旋密度波有序相中存在相变，但尚不能确定相变机制。使用HE3将测量范围扩展到0.6K。从较低温度下得到的结果可以发现，在整个温度范围内唯一的滑动机制可以用半经典图像来理解。结果表明，阈值电场随样品截面积的减小而增大，薄样品的阈值电场与粗晶样品的阈值电场的温度关系不同。指出晶体表面对密度波的钉扎和滑动是有效的。在脉冲电流作用下观察到响应电压波形的暂态振荡。其频率与电流的非线性分量成正比，等于直流电流作用下的窄带噪声频率。它的比例常数与温度无关，与滑动速度成正比。较少

Electrical conductivity of (TMTSF)_2AsF_6, a typical organic charge transfer salt was studied. Pressure, temperature and electric field-dependences of the conductivity were obtained. The metal-semimetal transition temperature and the thermal activation energy in the spin-density wave phase were determined as functions of pressure. It was concluded that the metal-semimetal transition is not associated with the normal to the spin-density wave transition ; a semi-metallic spin-density wave phase exists above the transition temperature especially near the critical presure At moderate pressure, the threshold electric field for the non-linear conductivity due to the sliding of the spin-density wave was obtained as the function of temperature. The results were compared with the theory by Maki and others. It is likely that the spin-density wave in this system in the temperature range above 3K is pinned by the commensurability with the lattice, not by impurities. This is the first finding of th … More e spin-density wave with the commensurate wave vector among the Bechgaard salts. It was that the temperature dependences of both the threshold field and of the non-linear conductivity change at 3K under low pressure. From the results, it was concluded that there is a phase transition in the spin-density wave ordered phase, though it has not been possible to identify the trasiton mechanism. The measurements were extended down to 0.6K using He3. From results obtained at lower temperature, it was found that the sliding mechanism unique in the entire temperature range can be understood in terms of a semi-classical picture. It was found that the threshold field increases with decreasing cross-sectional area of samples, and that the temperature dependence of the threshold field of thin samples is different from that of thick crystals. It was pointed out that furface of crystals is effective in pinning and sliding of density waves. Transient oscillation was observed in response voltage wave form under pulse current. Its frequency is proportional to the non-linear component of current and is equal to the frequency of narrow band noise under DC current. Its proportionality constant, independent of temperature, is proportional to the sliding velocity. Less