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Development of high-frequency impedance measurement under magnetic fields over wide range of temperature

宽温磁场下高频阻抗测量的发展

基本信息

批准号：
07555022
负责人：
MAEDA Atsutaka
金额：
$ 5.25万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

To study the low energy excitation in the highly correlated electrons and vortices in superconductors, we have developed two kinds of apparatuses that can measure the high-frequency impedance under magnetic fields over wide range of temperature. First, we constructed a surface resistance measurement system based on a bolometric technique. In this system, samples were located inside the cavity resonator to specify the RF field direction. Although the sensitivity of the bolometer decreases with increasing temperature, we could extend the upper limit of temperature over 80 K by the optimization of various conditions. Furthermore, we succeeded in measuring the-surface resistance as function of temperature instead of applied field. This is important for superconductors because the field inhomogeneity, which is originated from the pinning effect, can be excluded. Using the above system, we investigated the Josephson plasma resonance in high-T_c superconductors. Secondly, we constructed a system that can measure the surface resistance and the surface reactance simultaneously by applying a cavity perturbation technique. We prepared several cavities whose resonant frequencies were up to 98 GHz. Typical Q-factors of the cavities were about 10^4 and the reproducibility of the resonant frequency and the Q-factor were 10^<-6> and 10^<-3>, respectively. This system should also be useful to determine the absolute value of the surface impedance.

为了研究超导体中高关联电子和涡旋的低能激发，我们研制了两种能在宽温度范围内测量磁场作用下的高频阻抗的装置。首先，我们建立了一个基于测热技术的表面电阻测量系统。在该系统中，样品位于空腔谐振器内以指定RF场方向。虽然测辐射热计的灵敏度随温度的升高而降低，但通过各种条件的优化，我们可以将温度上限扩展到80 K以上。此外，我们成功地测量了表面电阻作为温度的函数，而不是施加的电场。这对超导体很重要，因为可以排除由钉扎效应引起的场不均匀性。利用上述系统，我们研究了高温超导体中的约瑟夫森等离子体共振。其次，我们利用腔微扰技术，建立了一个可以同时测量表面电阻和表面电抗的系统。我们准备了几个谐振频率高达98 GHz的腔体。谐振腔的典型品质因数约为10^4，谐振频率和品质因数的再现性分别为10^1<-6>和<-3>10^2。该系统还可用于确定表面阻抗的绝对值。