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Dr. Stephen K. Remillard, Physics

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Second and third order intermodulation (IM) signals in two superconducting microwave devices are measured before, during, and after the application of an approximately 50G static magnetic field. Each device under test is a roughly identical thin film YBa2Cu3O7−δ (YBCO) hairpin microwave resonator with a resonant frequency of approximately 840MHz. The first sample contains columnar defects orthogonal to the transmission line on its magnetic end. The second (control) sample contains no engineered defects. The defects were produced by irradiation of the sample with a beam of 250 MeV Au ions and serve as pinning centers for trapped magnetic flux. Flux pinning is a significant component of microwave nonlinearity in superconducting devices, which links pinning to the strength of produced IM. Second order IM in the control sample exhibits three distinct temperature dependent relaxation processes: an “ultrafast” exponential decay of unknown origin with a time constant on the order of 10-1 seconds, a fast exponential decay due to remanent demagnetization with a time constant on the order of 101 seconds, and a slow logarithmic relaxation due to Bean-Livingston surface barrier penetration with a duration on the order of 102 seconds. The irradiated sample does not exhibit the fast process. The influence of magnetic fluxons on second order IM is compared with the influence on third order IM, and the contributions of the columnar defects to each influence are examined.


This material is based upon work supported by the National Science Foundation under Grant No. 1505617.

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