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

高温氧化物超导体的场效应因其低载流子密度和短相干长度的特性有望应用于超导三端器件，但要实现高品质超薄器件存在很多困难。几纳米厚度的ETSC薄膜和大介电常数的绝缘层仍然存在，从另一个角度来看，倾斜晶界不仅表现为约瑟夫森结，而且具有大介电常数。由于晶界缺氧，导致载流子局部缺乏，导致场敏感性降低。在这项研究中，我们研究了 YBCO 薄膜人工晶界的电场效应，并获得了以下结果。・评估了晶界的载流子密度根据对毗邻两个超导电 YBCO 晶粒的正常导电人造晶界的电场效应的测量，结果为 2-5*10^<20>cm^<-3> 载流子密度低了 1 级。与晶粒内部相比，预计会有较大的电场效应，这是表明晶粒边界作为场效应通道的有用性的第一个结果。・作为相对于 AC 和 DC 的电场效应，约瑟夫森对晶界的影响表现为约瑟夫森。对于前一种效应，我们观察到了临界电流 I_c 和自谐振频率的电场调制，结果表明 I_c 中的场效应可以通过晶界结中的电荷载流子调制来定性地解释。对于后一个模型，谐振频率的变化归因于有效介电常数 epsilon^GB_/d 的变化，反映了用作基板的 STO 介电常数的场强依赖性 epsilon^ 的电场调制。 GB_/d可能适用于磁通流振荡器(FFO)较小情况下在晶界传输的电磁波的相速度控制。