聚焦氦离子束直接构图Y-Ba-Cu-O纳米约瑟夫森超导隧道结
Nano Josephson Superconducting Tunnel Junctions in Y-Ba-Cu-O Direct- Patterned with a Focused Helium Ion Beam
摘要：
自从发现非常规的氧化铜高转变温度超导体（HTS）以来，研究人员已经探索了许多方法来制造超导隧道结，这些材料既用于在液氮（77 K）的实际温度下运行的超导电子学，也用于测试和指导这些卓越超导体理论所必需的基本测量。困难在于超导相干长度的传统估计非常短，并且在这些材料中是各向异性的，通常在a-b平面中为~2 nm，沿c轴为~0.2 nm。相干体积包含非常少的超导对，因此即使存在小尺度的不均匀性也可以局部破坏超导性，这与传统超导体不同。因此，约瑟夫森结的电学性质对原子尺度上的化学变化和结构缺陷敏感，因此为了制造多个均匀的HTS结，需要在原子水平上进行控制。在这封信中，我们展示了非常高质量的所有高温超导约瑟夫森超导隧道结（约瑟夫森和准粒子隧穿）创建使用直径为500 μ m的氦离子束聚焦直接写入隧道势垒到YBa 2Cu 3 O 7（YBCO）薄膜。通过这种方法，我们证明了通过改变辐照剂量来连续控制从导电到绝缘的阻挡特性的能力。该技术为在实际温度（~77 K）下操作的量子力学电路的放大提供了可靠且可再现的途径，并且为基础科学在HTS中进行超导隧穿研究提供了途径。
英文摘要：
Since the discovery of the unconventional copper-oxide high-transition-temperature superconductors (HTS), researchers have explored many methods to fabricate superconducting tunnel junctions from these materials for both superconducting electronics operating at the practical temperature of liquid nitrogen (77 K) and for fundamental measurements essential for testing and guiding theories of these remarkable superconductors. The difficulty is that the traditional estimate of the superconducting coherence length is very short and anisotropic in these materials, typically ~2 nm in the a-b plane and ~0.2 nm along the c-axis. The coherence volume encloses very few superconducting pairs, so even the presence of small scale inhomogeneities can locally disrupt superconductivity unlike in conventional superconductors. Therefore the electrical properties of Josephson junctions are sensitive to chemical variations and structural defects on atomic length scales, thus to make multiple uniform HTS junctions, control at the atomic level is required. In this letter, we demonstrate very high-quality all-HTS Josephson superconducting tunnel junctions (both Josephson and quasiparticle tunneling) created by using a 500 pm diameter focused beam of helium ions to direct-write tunnel barriers into YBa2Cu3O7(YBCO) thin films. With this method we demonstrate the ability to control the barrier properties continuously from conducting to insulating by varying the irradiation dose. This technique provides a reliable and reproducible pathway for the scaling up of quantum mechanical circuits operating at practical temperatures (~77 K) as well as an avenue to conduct superconducting tunneling studies in HTS for basic science.
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