Evidence of unconvensional density wave in low dimensional organic compounds

在使用腔体的电子自旋共振（ESR）测量中，为了使频率稳定，温度被很好地控制为恒定是重要的。在ESR测量系统中，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通过IEEE-488接口连接到计算机。有机化合物λ-（BEDT-TSF）_2Fe_xCl_4<1-x>（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9 K以上表现为顺磁金属，在9 K以下变为反铁磁绝缘体。随着Ga浓度x增加，金属绝缘体转变温度降低。当x&gt;5.0时，出现超导相。对于x= ...更多信息 0时，通过介电响应、比热、质子NMR和X射线衍射测量，以及在9 K时的金属-绝缘体转变，报告了π电子中的异常。在1.5 - 300 K的温度范围内测量了g值和沿着H//a^*，H//B^* 和H//c的线宽，在20 ~ 300 K的温度范围内测量了磁场方向的依赖性。对x=0的晶体，在7 ~ 300 K温度范围内，只观察到一个共振信号。在120 K的磁场方向依赖性不显示二维导电平面的对称性。因此，来自π电子的响应与来自Fe离子的d电子的响应相结合。在70 K以下，g值发生了漂移，线宽增大。ESR异常伴随着π电子的异常，这是强π-d耦合的有力证据，对于x=0.4的晶体，也观察到类似的ESR异常。这表明除了x=0之外，化合物中也存在介电异常。在x=1.0的晶体的情况下，温度依赖性和磁场方向依赖性都表明ESR信号如预期的那样源自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