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TUCXA02 |
RF Vortex Nucleation in Superconductors within Time-Dependent Ginzburg-Landau Theory: Role of Surface Defects | |
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Funding: This work is funded by US Department of Energy / High Energy Physics through grant # DE-SC0017931 and the Maryland Quantum Materials Center. We use time-dependent Ginzburg-Landau (TDGL) numerical simulations to study the nucleation of RF vortices in Nb in the presence of surface defects when the material is subjected to an intense RF magnetic field in the GHz regime. In this work, we solve the TDGL equations, and Maxwell¿s equations, for a spatially nonuniform RF magnetic field created by a point RF magnetic dipole above the Nb surface. Here surface defects are notionally modeled as grain boundaries filled with a low-Tc impurity, such as oxidized Nb. The dynamics of RF currents induced in the resulting proximity-coupled superconductor are studied, and it is observed that RF vortex semi-loops penetrate the surface through the grain boundaries. Besides the RF vortex dynamics, the resulting third harmonic nonlinear response of the superconductor is calculated, and is shown to be closely related to RF vortex nucleation. The simulations show that RF vortex nucleation by surface defects can be studied by analyzing the third harmonic response of the superconductor. We make connections between these numerical studies and the results of our scanned near-field microwave microscopy efforts on a variety of SRF materials. |
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