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Research on High Tc superconducting three terminal devices utilizing the function of grain boundary

利用晶界作用的高温超导三端器件研究

基本信息

批准号：
06650349
负责人：
NAKAJIMA Kensuke
金额：
$ 1.47万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-06650349/
关键词：
High Tc Superconductivity Three terminal device Josephson junction Grain boundary 電界効果人工粒界 YBCO

项目摘要

Field effects of High-T_c Oxide Superconductors expected from their characterisctics of low carrier densities and short coherent lengths are hopefully applicable to superconducting three terminal devices. To achieve actual devices, however, a lot of difficulties, i. e fabrication of high quality ultra thin ETSC films with the thickness of several nm and development of insulating layr with a large dielectric constant still remains. From the another point of view, tilt grain boundaries not only behave as Josephson junctions but also have a large field sensitiviy because of local deficiency of charge carriers due to oxygen deficiency in the boundaries.In this research, we have investigated the electric field effects on artificial grain boundaries of YBCO films and obtained following results.・The carrier density of the grain boundary was evaluated to be 2-5*10^<20>cm^<-3> from the measurement of the electric field effect on a normal conducting artificial grain boundary adjoining two superc … More onducting YBCO grains. The carrier density was one drder lower than that in inner grains so that large electric field effects were expected. This is the first result indicating the usefulness of grain boudaries as field effect channels.・As electric field effects with respect to AC and DC Josephson effects on the grain boundaries behaving as Josephson junctions, electric field modulations of both critical current, I_c and self resonance frequency were observed. For former effect, it was shown that the field effect in I_c was qualititavely explained by a charge carrier modulation in grain boundary junctions on the basis of the SNS model. For later one, the variations of the resonance frequencies were attributed to changes in the effective dielectric constants, epsilon^GB_/d reflecting the field strength dependence ofthe dielectric constant of STO used as substrates. The electric field modulation of epsilon^GB_/d is possibly applicable to the phase velocity control of electromagnetic waves transmitting in the grain boundaries in the case of Flux Flow Oscilator (FFO). Less

高T_c氧化物超导体具有低载流子密度和短相干长度的特点，其场效应有望应用于超导三端器件。然而，要实现实际的器件，还存在很多困难.制备几nm厚的高质量超薄ETSC薄膜和开发具有大介电常数的绝缘层仍然是一个需要解决的问题。从另一个角度看，倾斜晶界不仅表现为约瑟夫森结，而且由于晶界中氧的缺乏，导致载流子的局部缺乏，使倾斜晶界具有很大的场敏感性.本文研究了电场对YBCO薄膜人工晶界的影响，得到以下结果.通过<20><-3>测量邻近两个超级电容器的正常导电人工晶界上的电场效应，估计晶界的载流子密度为2-5*10^ cm^ ...更多信息制备YBCO晶粒。载流子密度比晶粒内部低一个数量级，因此预期会产生大的电场效应。这是第一个表明晶粒边界作为场效应通道的有用性的结果。·由于电场对晶界的交、直流约瑟夫森效应的影响，观察到电场对临界电流、Ic和自谐振频率的调制。对于前者，本文用SNS模型定性地解释了I_c中的场效应是晶界结中的载流子调制。对于后者，谐振频率的变化归因于有效介电常数的变化，反映了STO作为衬底的介电常数与场强的关系。在磁通流振荡器（FFO）情况下，电场调制的Δ G/d可能适用于电磁波在晶界传播的相速度控制。少