本征约瑟夫森结与超导金属膜界面性质研究及相关器件制备

Exploring stable high-temperature superconducting SQUID and array preparation process is the urgent need to solve the core problem of high temperature superconducting Josephson devices. For the coherence length of high temperatue superconductor is very short (less than 1nm), prepared samples, applying traditional methods such as: grain boundary junction, step-edge junction, proximity effect junction, are usually unstable. Based on the intrinsic Josephson effect of the layered copper oxide superconductor, provided by the stable nature of the inner crystal structure, the junction and the junction between the superconducting electrodes connected to become a high quality SQUID and array devices. Single junctions fabricated using low-temperature single-crystal cleavage, vacuum in situ rapid evaporation of the metal electrode; connection between the knot and the knot with BiSrCaCuO (2212) / stable metal / superconducting metals program, through the establishment of the proximity effect model and experimental validation of combination of methods to achieve the device internal superconducting circuit. Combined with low-temperature superconducting existing theory and experience in the field, the design prepared Qubit Squid has the largest magnetic field modulation depth and the maximum coupling strength. Study high-temperature superconducting SQUID and array low-temperature physical properties, revealing the d-wave superconducting electron pairing under the conditions of new quantum mechanics. Therefore, the implementation of this project for the research to lay the theoretical and technical basis.

探索稳定的高温超导SQUID等器件制备工艺是高温超导约瑟夫森器件研究亟待解决的核心问题。由于高温超导相干长度很短（小于1nm），应用传统方法如：晶界结、台阶结、邻近效应结等制备出的样品稳定性不足。本项目利用层状铜氧化物超导体内存在的本征约瑟夫森效应，制备出性质稳定的约瑟夫森结，结和结之间由超导电极相连成为高质量SQUID和阵列等器件。单个结的制备采用低温解理单晶，真空原位快速蒸发金属电极的方法；结和结之间的连接采用BiSrCaCuO(2212)/稳定金属/超导金属方案，通过建立邻近效应模型和实验验证相结合方法，实现器件内部超导通路。结合低温超导领域已有理论和经验，设计制备出具有最大磁场调制深度的SQUID和阵列。研究高温超导SQUID和阵列的低温物理特性，揭示d波超导电子配对条件下新颖的量子力学规律。因此，本项目的实施可以为相关研究奠定理论和技术基础。

温超导材料结构复杂及相干长度短，这限制了高温超导电子器件的深入发展。高温超导体特别是BiSrCaCuO（Bi-2212）内部存在本征的约瑟夫森效应，相比人为加工的约瑟夫森结，本征约瑟夫森结有着突出的优点：它制作工艺简单，重复性好，稳定性高。然而，如何在一块单晶上制备多个本征约瑟夫森结，使他们按照设计要求很好的集成起来，形成超导回路，这是一个亟需解决的问题。本项目以高温超导体和常规超导体的界面为研究对象，摸索出这类结构的制备工艺，并研究其物理性质。项目采用Bi-2212/稳定金属/超导金属方案，通过真空原位解理单晶，快速蒸发金属电极的方法，实现了Bi-2212和稳定金属之间干净理想界面的制备。用四端法表征其性质，结果显示：表面铜氧层与内部铜氧层具有相同的超导转变温度，界面电阻大约为0.3欧姆（样品横截面积100平方微米），比已经报道的结果降低了一个量级。在极低噪声环境的系统中更加细致的表征显示：流过Bi-2212/稳定金属/超导金属结构中的电流不存在约瑟夫森电流，理论分析显示理想掺杂Bi-2212中d波配对占据主导地位，s波分量相对d波分量小6个量级以上。本项目从实验上展示了d波超导体和s波超导体之间新奇的隧穿现象，为相关研究奠定了理论和技术基础。