Anlage Research Group |
| High Frequency Superconductivity, Microscopy, Nanophysics, and Chaos |
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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 is supported by the National Science Foundation 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) .
90. Sheng-Chiang Lee and Steven M. Anlage, “Spatially Resolved Nonlinearity Measurements of YBa2Cu3O7-d Bi-crystal Grain Boundaries,” Appl. Phys. Lett. 82, 1893-1895 (2003).
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) .
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).
106. Sheng-Chiang Lee, Su-Young Lee, and Steven M. Anlage, “Microwave Nonlinearities of an Isolated Long YBa2Cu3O7-d Bicrystal Grain Boundary,” Phys. Rev. B 72 , 024527 (2005).
127. Dragos I. Mircea, Sheng-Chiang Lee, M. C. Sullivan, Benjamin S. Palmer, Boris Maiorov, and Steven M. Anlage, “Evidence for Fluctuation-induced Resistive Microwave Nonlinearities above Tc in Underdoped Cuprates,” submitted to Phys. Rev. B.
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