Evidence of unconvensional density wave in low dimensional organic compounds

在使用腔体进行电子自旋共振（ESR）测量时，为了使频率稳定，必须很好地控制温度以保持恒定。在ESR测量系统中，通过IEEE-488接口将用于检测输出的锁相放大器、用于精确磁场控制的恒压发生器和温度控制器与计算机相连。利用LabVIEW软件编制了自动测量程序。有机化合物λ-(BEDT-TSF)_2Fe_<1-x>Ga_xCl_4（x=0,0.4,1.0）是n-d体系的典型例子。BEDT-TSF分子中的Π电子与Fe离子中的d电子之间存在很强的相关性。当x=0时，材料在9K以上表现为顺磁性金属，在9K以下变为反铁磁绝缘体。随着Ga浓度x的增加，金属绝缘子转变温度降低。当x>5.0时，出现超导相。对于x=…> 0的材料，在70 K左右的介电响应、比热、质子核磁共振和x射线衍射测量以及在9 K时的金属绝缘体跃迁都报告了π电子的异常。在1.5 ~ 300 K的温度范围内测量了沿H//a^*、H//b^*和H//c的g值和线宽，在20 ~ 300 K的几个温度范围内测量了磁场方向依赖关系。在x=0晶体的ESR测量中，在7 ~ 300 K温度范围内只观察到一个共振信号。在120k时，磁场方向依赖关系不显示二维导电平面的对称性。因此，π电子的响应与铁离子的d电子的响应结合在一起。在70 K以下观察到g值的偏移和线宽的增强。π电子的ESR异常伴随π电子的异常发生，是π-d强耦合的有力证据。对于x=0.4的晶体，ESR信号也出现了类似的异常。这表明除了x=0外，化合物中也存在介电异常。在x=1.0晶体的情况下，温度依赖关系和磁场方向依赖关系都表明，ESR信号来源于π电子。少

In a electron spin resonance (ESR) measurement by using a cavity, it is important that the temperature is well controlled to be constant in order that the frequency should be stable. In the ESR measurement system, a lock-in amplifier to detect output, a constant voltage generator for the precise magnetic field control and the temperature controller are connected to a computer through IEEE-488 interface. The program is made to conduct the measurement automatically by using LabVIEW software.The organic compound λ-(BEDT-TSF)_2Fe_<1-x>Ga_xCl_4(x=0,0.4,1.0) is the typical example of so called n-d system. There is the strong correlation between the Π electrons at the BEDT-TSF molecules and the d electrons at Fe ions. For x=0, the material shows the paramagnetic metal above 9K and it becomes the antiferromagnetic insulator below 9 K. As the Ga concentration x increases, the metal insulator transition temperature decreases. For x>5.0, the superconducting phase appears. For the material with x= … More 0, the anomaly in the π electrons are reported by the dielectric response, the specific heat, the proton NMR and the X-ray diffraction measurements at around 70 K in addition to the metal insulator transition at 9 K.The g-value and the line width along H//a^*, H//b^* and H//c are measured in the temperature range from 1.5 to 300 K, The magnetic field direction dependencies are measured at several temperatures between 20 and 300 K. In the ESR measurements for the crystal with x=0, only one resonance signals observed in the temperature range from 7 to 300 K. The magnetic field direction dependencies at 120 K do not show the symmetry of the two-dimensional conducting plane. Therefore, the response from the π electrons is combined with that from the d electrons of Fe ions. The shift of the g-value and the enhancement of the line width are observed below 70 K. It is a strong evidence of the strong π-d coupling that the ESR anomaly occurs accompanied by the anomaly in the π electrons.For the crystal with x=0.4, similar anomaly in the ESR signal is observed. This suggests the dielectric anomaly also in the compounds except for x=0. In the case of the crystal with x=1.0, both of the temperature dependencies and magnetic field direction dependencies show that the ESR signal originates from the π electrons as expected. Less