Mgb2 Nonlinear Properties Investigated under Localized High RF Magnetic Field Excitation

Abstract

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).

6 pages, 6 figures

References in corpus (11)

• Intrinsic Josephson effect and nonequilibrium soliton structures in two-gap superconductors
• Dynamics of vortex penetration, jumpwise instabilities and nonlinear surface resistance of type-II superconductors in strong rf fields
• Doping-Dependent Nonlinear Meissner Effect and Spontaneous Currents in High-Tc Superconductors
• Nonlinear microwave response of MgB2
• Microwave Nonlinearities of an Isolated Long YBa_2Cu_3O_(7-d) Bi-crystal Grain Boundary
• Pinning and creation of vortices in superconducting films by a magnetic dipole
• Phase-sensitive Harmonic Measurements of Microwave Nonlinearities in Cuprate Thin Films
• Strong surface contribution to the Nonlinear Meissner Effect
• Nonlinear Near-Field Microwave Microscope For RF Defect Localization in Superconductors
• Intrinsic nonlinearity probed by intermodulation distortion microwave measurements on high quality MgB2 thin films
• Nonlinear current response of one- and two-band superconductors