Carrier doping into the molecular insulators and exploration of novel phases

在本研究中，我们针对基于a)BEDT-TTf和b)DCNQI分子的关联诱导分子绝缘体中掺杂载流子，探索了可能的新相。a)(BEDT-TTf)_4X[X=Hg_&lt；2.89&gt；Br8Hg_&lt；2.78&gt；Cl8]一类具有半填充带的二维有机系统κ-(BEDT-TTf)_2X跨越了超导相和反铁磁相之间的一阶Mott转变的相图。在本研究中，我们首先测量了掺杂有机Mott绝缘体κ-(BEDT-TTf)_4Hg&lt；2.78&gt；Cl8的核磁共振谱和弛豫速率1/T，L/(T_1T)继续按1/T的比例增加，下降到100mK，然后形成一个宽峰。光谱显示出低温展宽，表明了短程AF有序化，但不是三维有序化。这是首次观测到有机化合物中的量子临界自旋涨落，这与广泛研究的具有固定能带填充的κ-(BEDT-TTf)_2X的情况形成了惊人的对比。b)(DI-DCNO1)_2M(DI-DCNQI)_2AG是一种顺磁性绝缘体，它具有准一维的四分之一填充的π带。通过~&lt；13&gt；C-核磁共振研究发现，该绝缘相是通过在银位上掺入铜来尝试载流子掺杂而形成的电荷缠绕状态。随着铜含量的增加，带电带隙绝缘子转变为无带隙绝缘子，具有可变范围的跳跃行为，最后是金属相。这一结果显示了电荷有序的崩塌方式和随着载流子和无序的引入而进入金属相的途径。

In the present study, we aim at doping carriers into the correlation-induced molecular insulators based on a) BEDT-TTF and b) DCNQI molecules, and explore possible novel phases.a) (BEDT-TTF)_4X [X=Hg_<2.89>Br_8Hg_<2.78>Cl_8]A family of two-dimensional organic systems, κ-(BEDT-TTF)_2X, with half-filled bands span the phase diagram of the 1 st-order Mott transition between the superconducting and antiferromagnetic phases as a function of band-width. In the present sudy, we first measured the ^<13>C-NMR spectra and relaxation rate, 1/T, for a doped organic Mott insulator, κ-(BEDT-TTF)_4Hg_<2.78>Cl_8, down to 30 mK.The l/(T_1T) continues to increase in proportion to 1/T down to 100 mK and then forms a broad peak. The spectra show low-temperature broadening indicative of the short-range AF ordering, but not the three-dimensional one. This is the first observation of the quantum critical spin fluctuations in organics and indicates a surprising contrast to the widely studied case of κ-(BEDT-TTF)_2X with fixed band-filling.b) (DI-DCNOl)_2M(DI-DCNQI)_2Ag, which has a quasi-one-dimensional quarter-filled π band, is a paramagnetic insulator. By ^<13>C-NMR study, this insulating phase is found to be in a charge-rodered state, into which the carrier doping was attempted by Cu doping into the Ag sites. As the Cu content is increased, the charge-gapped insulator changes to the nongapped insulator with the variable range hopping behaviour, eventually followed by the metallic phase. This result shows a manner of the collapse of the charge ordering and a route to the metallic phase with introduction of carriers and disorder.