|Nonlinear Properties of Superconductors|
One of the characteristics of superconductivity is the Meissner effect. A superconductor will actively screen out a static or dynamic magnetic field from its interior. It does so by generating a diamagnetic screening current within a penetration depth of its surface. However the superconductor must pay an energy penalty for creating this current and this leads to degradation of the superfluid density. This is a nonlinearity intrinsic to the superconductor. This nonlinearity is most easily measured with sensitive microwave techniques such as harmonic generation and intermodulation distortion.
We developed the first microscopes capable of making quantitative spatially-resolved images of intrinsic and extrinsic superconducting nonlinearities. We have imaged the intermodulation electric fields above a superconducting microwave resonator (papers 62, 66, 71). Another microscope was developed to image harmonic generation from a single Josephson junction in a high-Tc film. The images are in quantitative agreement with numerical models of vortex generation and motion in the junction, induced by the measurement current (papers 90, 93, 106). The microscope was also used to measure the temperature and doping dependence of nonlinear response near Tc in under-doped and optimally-doped cuprate materials (papers 93, 102, 127). It was discovered that nonlinear response extends well above Tc in the under-doped cuprates in the pseudo-gap phase. This work now continues with Department of Energy support to investigate the local origins of quench phenomena in bulk Nb superconductors used in superconducitng RF applications (papers 138, 154). For this work we have developed a high-RF-field localized microwave microscope that can produce fields that locally exceed the thermodynamic critical field of bulk Nb (~ 200 mT).
See our related work on the nonlinear properties of superconductors investigated through laser scanning microscopy.
This work is supported by the National Science Foundation, Department of Energy, and the Maryland Center for Nanophysics and Advanced Materials.
Some relevant papers: (All papers can be downloaded from the full publication list)
62. Ashfaq S. Thanawalla, S. K. Dutta, C. P. Vlahacos, D. E. Steinhauer, B. J. Feenstra, Steven M. Anlage, and F. C. Wellstood, "Microwave Near-Field Imaging of Electric Fields in a Superconducting Microstrip Resonator," Appl. Phys. Lett. 73, 2491-2493 (1998) .
66. Steven M. Anlage, Wensheng Hu, C. P. Vlahacos, David Steinhauer, B. J. Feenstra, Sudeep K. Dutta, Ashfaq Thanawalla, and F. C. Wellstood, "Microwave Nonlinearities in High-Tc Superconductors: The Truth Is Out There," J. Supercond. 12, 3 53-362 (1999) .
71. Wensheng Hu, B. J. Feenstra, A. S. Thanawalla, F. C. Wellstood, and Steven M. Anlage, "Imaging of Microwave Intermodulation Fields in a Superconducting Microstrip Resonator," Appl. Phys. Lett. 75, 2824-2826 (1999) . pdf
93. Sheng-Chiang Lee and Steven M. Anlage, “Study of Local Nonlinear Properties Using a Near-Field Microwave Microscope,” IEEE Trans. Applied Supercond. 13, 3594-3597 (2003) . pdf
102. Sheng-Chiang Lee, Mathew Sullivan, Gregory R. Ruchti, Steven M. Anlage, Benjamin Palmer, B. Maiorov, E. Osquiguil, “Doping-Dependent Nonlinear Meissner Effect and Spontaneous Currents in High-Tc Superconductors,” Phys. Rev. B 71, 014507 (2005). pdfIEEE Trans. Appl. Supercond. 21, 2615-2618 (2011). pdf
154. Tamin Tai, Behnood G. Ghamsari, Steven M. Anlage, C. G. Zhuang, X. X. Xi, “MgB2 nonlinear properties investigated under localized high rf magnetic field excitation,” Phys. Rev. ST Accel. Beams 15, 122002 (2012). pdf
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