The Collapse or Melting of the Charge Order in Organic Conductors

通过(DI-DCNQI)_2Ag和θ-(Et)_2RbZn(SCN)_4的输运和核磁共振测量，研究了有机导体中电荷有序的崩塌或熔化。(DI-DCNQ)_2AG具有准一维的四分之一填充带，其电荷有序现象得到了核磁共振、核磁共振、核磁共振和X-射线衍射谱的证实。这个系统在压力下已经金属化了。研究发现，电荷顺序熔化成一种奇特的金属状态，与电阻率的立方温度相关。我们构建了压力-温度相图，其中熔化线有一个临界点，它在低压下有一个三临界点，在高压下有一个临界点，在它消失之前。8-(Et)_2RbZn(SCN)_4具有准二维的四分之一填充带，具有三角形的Et晶格，这对半填充带系中的电荷位置和自旋排列造成了阻碍。当缓慢冷却时，它经历了电荷有序和晶格调制的强烈耦合。然而，如果它被迅速冷却，在室温下很尖锐的核磁共振谱变宽，弛豫速率变得不均匀。我们对这两个态进行了T_2测量，特别注意了后一个电子态的性质。研究发现，核磁共振的不均匀特征是受挫驱动的非均匀电荷的表现，可称为电荷玻璃。

The collapse or melting of the charge order in organic conductors have been studied by the transport and NMR measurements of (DI-DCNQI)_2Ag and θ-(ET)_2RbZn(SCN)_4.The (DI-DCNQI)_2Ag with a quasi-one-dimensional quarter-filled-band shows charge ordering, of which the evidences were provided by ^<13>C NMR, ^1H NMR and XRD measurements. This system has been metallized by pressure. It was found that the charge order melts into a curious metallic state with cubic temperature dependence of resistivity. We constructed the pressure-temperature phase diagram, where the melting line has a tricritical point dividing the second-order line at low pressures and the first-order line at high pressures just before it vanishes.The 8-(ET)_2RbZn(SCN)_4, with a quasi-two-dimensional quarter-filled band has triangular ET lattice, which imposes frustration on the charge location as on the spin alignment in the half-filled band system. It undergoes a charge ordering strongly coupled with the lattice modulation when cooled slowly. In case it is cooled rapidly, however, the NMR spectrum, which was sharp at room temperature, becomes broadened and the relaxation rate gets inhomogeneous. We have performed T_2 measurements on the two states, paying particular attention to the nature of the latter electronic state. It was found that the inhomogeneous NMR features are manifestations of the frustration-driven inhomogeneous charge, which can be called the charge glass.