A Study on Transport Mechanism in High-Temperature Superconductor Josephson Junctions and Their Application to 60K-Electronics

这项工作的目的是了解基于高温超导体的约瑟夫森结的输运机制，从而导致在60k下工作的“可用”约瑟夫森结。研究了具有不同电阻率的prba_2cu_30_7基势垒的Yba_2Cu_3O_7斜坡边Josephson结的电学性质。实验结果表明，粒子对的输运机制为直接隧穿，而准粒子的输运机制除直接隧穿外还为共振隧穿。我们还发现，势垒中局域态的高密度降低了质量参数IcRn产品，其中Ic和Rn分别是临界电流和结电阻。事实上，在具有高阻性ga掺杂PBCO势垒的结中，可以获得高达6mV的高IoRn值。我们面临着开发可用结的几个缺点。其中最严重的是Ic、Rn等结参数的大扩散。我们发现屏障或反电极的沉积增加了扩散。为了打破这种情况，我们开发了无人工屏障的约瑟夫森结，成功地减少了传播。

The purpose of this work is to understand the transport mechanisms in Josephson junctions based on high-temperature superconductors, leading to 'usable' Josephson junctions operating at 60 K.We study electrical properties of Yba_2Cu_3O_7 ramp-edge Josephson junctions with PrBa_2Cu_30_7-based barriers having different resistivities. Experimental results show that the transport mechanism of the pair particles is direct tunneling, whereas that of quasipartioles is resonant tunneling in addition to the direct tunneling. We also find that the high density of the localized states in the barriers reduces the quality parameter, IcRn products, where Ic and Rn are a critical current and a junction resistance, respectively. In fact, high IoRn values are obtained up to 6mV in the junctions with highly resistive Ga-doped PBCO barriers.We face the several drawbacks to the development of the usable junctions. The most serious one is the large spread of the junction parameters such as Ic, Rn. We find that the deposition of the barriers or counter-electrodes increase the spread. To break this situation, we have developed the Josephson junctions without artificial barriers and succeeded in the reduction of the spread.