Research of Quantum tunneling phenomena in mesoscopic Josephson superlattice

本文研究了（Bil-xPbx）_2Sr_2CaCu_2O_y单晶本征约瑟夫森超晶格中的量子隧穿现象。在本研究中，我们获得了以下结果.我们开发了一种新的制造工艺来制造一堆小的本征约瑟夫森结。通过使用该工艺，成功制备了横向尺寸从亚μm^2到几十μm^2的样品。2. BPSCCO本征约瑟夫森结的电流-电压特性显示出明显的多分支和高滞后，以及定义明确的间隙结构，没有负电阻。准粒子的I-V特性符合加权动量平均d波模型的特征.在中间温度下，从零电压状态到有限电压状态的切换机制是由于热激活过程。低温下，由于多种开关模式的影响，开关电流分布变宽.为了分析涡流的动力学特性，提出了考虑热涨落的感应耦合模型。该模型再现了以往的实验结果，并表明涡的异相流动是稳定的而非同相流动，涡流动阻力的振荡与涡格结构没有直接关系.使用该工艺成功地制作了具有面内回路几何结构和两个本征约瑟夫森结叠层的直流SQUID。由于叠层间的量子干涉，所制备的SQUID具有明显的周期性和对称性的磁通-电压特性.制备了Fe/BSCCO混合结构。在外加磁场后，观察到自旋注入对本征约瑟夫森结临界电流的抑制。

We studied quantum tunneling phenomena in intrinsic Josephson superlattice of (Bil-xPbx)_2Sr_2CaCu_2O_y single crystals. In this study, we obtained the following results.1. We developed the new fabricated process to make a stack of small intrinsic Josephson junctions. By using this process, samples with lateral dimensions ranging from sub-μm^2 to several tens μm^2 were successfully fabricated.2. The current-voltage characteristics of BPSCCO intrinsic Josephson junctions showed clear multiple branches with high hysteresis and a well-defined gap structure without negative resistance. The quasiparticle I-V characteristics were in agreement with the feature of a weighted, momentum-averaged d-wave model.3. At intermediate temperature the switching mechanism from zero voltage state to a finite voltage state is due to thermal activation process. At lower temperature switching current distribution became wider due to the influence of multiple switching modes.4. To analyze the vortex dynamics, the inductive coupling model taking into account thermal fluctuations was proposed. The model reproduced the previous experimental results and suggests that the out-of-phase flow of vortices is stable rather than the in-phase flow, and the oscillations of the vortex flow resistance are not directly related to the structure of the vortex lattice.5. The dc SQUIDs with in-plane loop geometry and two stacks of intrinsic Josephson junctions were successfully fabricated using the developed process. The fabricated SQUID showed clear periodic and symmetric flux-voltage characteristics due to the quantum interference between the stacks.6. The hybrid Fe/BSCCO structure was fabricated. After an application of a magnetic field, the suppression of the critical current of intrinsic Josephson junctions due to the spin injection was observed.