局部强磁场激励下Mgb2非线性特性的研究
Mgb2 Nonlinear Properties Investigated under Localized High RF Magnetic Field Excitation
摘要：
为了提高超导射频（SRF）腔体的加速梯度，二硼化镁（MgB 2）由于其高的转变温度和在高RF场区域中具有低表面电阻的潜力而打开了希望。然而，由于在π带中存在小的超导能隙，与诸如Nb的单能隙s波超导体（SC）相比，MgB 2的非线性响应潜在地相当大。了解非线性的机制，来自两个能带结构的MgB 2，以及外来的来源，是一个迫切的要求。由磁性写入头产生的局部和强RF磁场被集成到我们的非线性迈斯纳效应扫描微波显微镜中[1]。MgB 2薄膜厚度为50 nm，通过混合物理化学气相沉积技术在电介质基板上制造，在一个固定的位置进行测量，并显示出强烈的温度依赖性的三次谐波响应。我们建议，至少有两种机制是负责这种非线性响应，其中之一涉及涡旋成核和渗透到膜。[1]T. M. Tai，X. X. Xi角，澳-地G. Zhuang，D. I. Mircea，S. M.陈文辉，“非线性近场微波显微镜在超导体中的应用”，国立台湾大学电子工程学研究所硕士论文。21，2615（2011）。
英文摘要：
In order to increase the accelerating gradient of Superconducting Radio Frequency (SRF) cavities, Magnesium Diboride (MgB2) opens up hope because of its high transition temperature and potential for low surface resistance in the high RF field regime. However, due to the presence of the small superconducting gap in the π band, the nonlinear response of MgB2 is potentially quite large compared to a single gap s-wave superconductor (SC) such as Nb. Understanding the mechanisms of nonlinearity coming from the two-band structure of MgB2, as well as extrinsic sources, is an urgent requirement. A localized and strong RF magnetic field, created by a magnetic write head, is integrated into our nonlinear-Meissner-effect scanning microwave microscope [1]. MgB2 films with thickness 50 nm, fabricated by a hybrid physical-chemical vapor deposition technique on dielectric substrates, are measured at a fixed location and show a strongly temperature-dependent third harmonic response. We propose that at least two mechanisms are responsible for this nonlinear response, one of which involves vortex nucleation and penetration into the film. [1] T. M. Tai, X. X. Xi, C. G. Zhuang, D. I. Mircea, S. M. Anlage, "Nonlinear Near-Field Microwave Microscope for RF Defect Localization in Superconductors", IEEE Trans. Appl. Supercond. 21, 2615 (2011).
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