ESR and Cyclotron Resonance of Strongly Correlated Materials

继去年的实验之后，我们利用最新研制的矢量网络分析仪系统，在超低温、强磁场条件下对一些稀土化合物进行了磁共振和回旋共振实验。微波腔具有很高的灵敏度。频率范围为40 ~ 110 GHz，温度范围为0.5 ~ 300 K。所得结果如下：1)GdAs：用ESR测定了该化合物具有易（111）平面的磁性结构，这是迄今为止未知的。在0.5 K下观察到回旋共振，确定了载流子的有效质量为0.48 m0。这一结果表明，费米表面是球形的，有效质量是量子振荡得到的有效质量的两倍。2) LaSb：在4.2 K以下观测到回旋共振。从共振位置的各向异性行为来看，这种共振是由于具有椭球费米表面的载流子引起的。在<100>方向得到的有效质量为0.26 m0，是量子振荡得到的有效质量的2倍。在低维有机导体中，用回旋共振和量子振荡得到的质量存在差异。但前者大于后者，且与理论预测一致，这与我们的结果不符。在本研究中，我们首次在强相关材料上观察到从未报道过的回旋共振，并直接确定了有效质量。解释我们的结果的理论还没有建立起来。

Continuing the experiments done last year, we have performed the magnetic resonance and cyclotron resonance on some rare-earth compounds using vector network analyzer system developed recently at ultra low temperatures and high magnetic fields. A microwave cavity has been used for high sensitivity. The frequency range is 40〜110 GHz and the temperature range is 0.5〜300 K. The obtained results are as follows :1) GdAs : The magnetic structure of this compound with easy (111) plane, which had been unknown so far, has been determined by ESR. The cyclotron resonance has been observed at 0.5 K and the effective mass of the carrier is detemined as 0.48 m0. This result suggests that the fermi surface is spherical and the effective mass is two times larger than that obtained by quantum oscillation.2) LaSb : The cyclotron resonance has been observed below 4.2 K. From the anisotropic behavior of the resonance position, this resonance occurs due to carriers with a ellipsoidal fermi surface. The effective mass obtained is 0.26 m0 along the <100> direction and is two times larger than that obtained by quantum oscillation.The difference between masses obtained by cyclotron resonance and quantum oscillaation has been observed for low dimensional organic conductors. However the former is larger than the latter and consistent with the theoretical prediction, which is against our result. In this study, we have first observed the cyclotron resonance on strongly correlated materials, which has never reported, and determined the effective mass directly. The theory to explain our result has not been done yet.