The Properties of the Series of Organic Conductors (TMTSF)2X: Spin Density Waves and Charge Density Waves

Abstract

The series of one-dimensional organic conductors (TMTSF)2X, X = PF6-, AsF6-, NO3-, BF4-, ReO4-, ClO4- and others has shown a remarkable richness of interesting properties. Most members of the series become superconductors under modest pressures ranging from ambient to 15 kbar at temperatures between 0.9 and 1.6 K. Metal-insulator transitions occur in the majority of compounds in the family but the nature hereof and the transition temperature is widely different among the individual members: The hexafluorides seem to be very much alike and they all probably undergo antiferromagnetic phase transitions into spin density wave states near 15 K. By contrast the ReO4- compound undergoes a Peierls type of transition near 180 K. (TMTSF)2ClO4 does not undergo a complete metal-insulator transition and remains highly conducting down to 1.5 K at which temperature it becomes superconducting. However, an anomaly is found in the spin susceptibility of (TMTSF)2ClO4 near 6 K, so the existence of spin density waves in this material is not yet ruled out.Experimental results reported here include electron spin resonance, nuclear magnetic resonance, microwave conductivity, microwave dielectric constant and static magnetic susceptibility of various members of the family of organic conductors (TMTSF)2X.