Semifluxons in ferromagnetic Josephson junctions

铁磁约瑟夫森结中的半通量子

• 批准号: 163475902
• 负责人: Dr. Edward Goldobin
• 金额: --
• 依托单位: Physikalisches Institut
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2010
• 资助国家: 德国
• 起止时间: 2009-12-31 至 2013-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/163475902?language=en
• 关键词: Semifluxons; ferromagnetic; Josephson; junctions

In a O-π Josephson junction, vortices carrying only a half of the magnetic flux quantum (semifluxons) may appear spontaneously. The physics of such vortices has attracted a lot of interest both in view of their novel fundamental physics and in view of potential applications in superconducting electronics. Using superconductor-insulator-ferromagnet-superconductor (SIFS) technology O- π Josephson junctions with low damping (required when using Josephson junctions as active elements) and of almost arbitrary shape of both the junction and the O- π discontinuity can be fabricated. However, the existing technology has drawbacks: the maximum supercurrent density jc π in the π parts of the junctions is low (40 A/cm² or less), leading to a vortex size ( ) often exceeding 60 µm. Consequently, structures containing arrangements of several semifluxons are almost impossible to realize.Within this project we focus on (a) the further development of the ferromagnetic O- π Josephson junction technology and (b) the experimental investigation of semifluxons in such junctions.The technological aim is to substantially increase jc π in the π state (ideally by at least one order of magnitude), still keeping the junction normal state resistance Rn high and thus damping low. This will make fractional vortices (and devices) much smaller and suitable for circuits operating in either the classical or quantum regime. This aim will be persued by the following two routes. First, the existing (S|I|F|S) Josephson junction technology will be modified to include a clean ferromagnet with low damping. Second, the existing Superconductor-Ferromagnetic lnsulator-Superconductor (S|FIlS) Josephson junction technology (e.g., FI=FeSi) will be optimized in terms of stoichiometry and the thickness of the Fl-layer. The crossover from S|FI|S to S|F|S limit at high concentration of the ferromagnet will be investigated.Using these structures experiments will be performed in the temperature range between 300 mK and 6 K where the fractional vortices can be considered as classical nonlinear objects. The reduced vortex size will enable investigation of not yet explored multi-vortex systems such as two- or three-vortex molecules and even ID vortex crystals. The interaction of fractional vortices with each other, e.g., mutual flipping or splitting of eigenfrequencies, as well as interaction with integer fluxons will be studied.As a result, this project will push forward the ferromagnetic 0- π Josephson junction technology, which is also useful for many other applications such as self-biased classical and quantum circuits. The project will improve the understanding of the fractional vortex physics and may suggest new applications.

在O-π约瑟夫森结中，可能会自发地出现只携带一半磁通量量子的涡旋（半磁通子）。这种涡旋的物理特性吸引了很多人的兴趣，无论是在其新颖的基础物理，并在超导电子学的潜在应用。利用超导体-绝缘体-铁磁体-超导体（SIFS）技术，可以制备出具有低阻尼（当使用约瑟夫森结作为有源元件时需要）和几乎任意形状的结和O- π不连续的O- π约瑟夫森结。然而，现有技术存在缺点：结的π部分中的最大超电流密度jc π较低（40 A/cm²或更低），导致涡流尺寸（ 通常超过60 μm。因此，包含多个半流子排列的结构几乎是不可能实现的。在本项目中，我们着重于（a）铁磁O- π约瑟夫森结技术的进一步发展和（B）这种结中半流子的实验研究。技术目标是大幅度提高π态的jc π（理想地，至少一个数量级），仍然保持结正常状态电阻Rn高并且因此阻尼低。这将使分数涡旋（和设备）小得多，适用于在经典或量子状态下运行的电路。这一目标将通过以下两条途径实现。首先，现有的（S|我|F|约瑟夫森结技术将被修改，包括一个干净的低阻尼铁磁体。第二，现有的超导体-铁磁绝缘体-超导体（S|约瑟夫森结技术（例如，FI=FeSi）将在化学计量和FI层的厚度方面进行优化。从S的交叉|Fi| S到S| F|在300 mK ~ 6 K温度范围内，分数涡旋可以看作是经典的非线性对象，利用这些结构进行实验。减小的涡旋尺寸将使尚未探索的多涡旋系统，如两个或三个涡旋分子，甚至ID涡旋晶体的调查。分数涡相互作用，例如，本课题将研究本征频率的相互翻转或分裂，以及与整数磁通子的相互作用，从而推动铁磁0- π约瑟夫森结技术的发展，这对自偏置经典电路和量子电路等许多应用也是有用的。该项目将提高分数涡物理学的理解，并可能提出新的应用。