Nonlinearities give rise to intermodulation distortion in superconducting microwave devices and currently limit their use to low power applications. We have developed a cryogenic imaging technique to spatially resolve intermodulation distortion and used it to image an 8.2 GHz high temperature superconducting Tl2Ba2CaCu2O8 microwave resonator. The images reveal that the fundamental and intermodulation electric fields obey a fixed relation throughout the device. We note that further refinements of intermodulation theory in resonant devices may be required to fully describe the data.
We have developed scanning near-field microwave microscopes which can image electrodynamic properties of superconducting materials on length scales down to about 2 Fm. The microscopes are capable of quantitative imaging o f sheet resistance of thin films, and surface topography.We demonstrate the utility of the microscopes through images of the sheet resistance of a YBa2Cu307.s thin film wafer, images of bulk Nb surfaces, and spatially resolved measurements of T, of a YBazCujO,.s thin film. We also discuss some o f the limitations of the microscope and conclude with a summary of its present capabilities.
Abstract-We have developed a scanning near-field microwave microscope that operates at cryogenic temperatures. Our system uses an open-ended coaxial probe with a 200 µ µm inner conductor diameter and operates from 77 to 300 K in the 0.01-20 GHz frequency range. In this paper, we present microwave images of the electric field distribution above a Tl 2 Ba 2 CaCu 2 O 8 microstrip resonator at 77 K, measured at several heights. In addition, we describe the use of a frequency-following circuit to study the influence of the probe on the resonant frequency of the device.
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