Imaging of microwave intermodulation fields in a superconducting microstrip resonator

Abstract

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.

Microwave nonlinearities of an isolated longYBa2Cu3O7−δbicrystal grain boundary

“…17,19 Most of these experiments are done with resonant techniques, which by their nature study the averaged nonlinear response from the whole sample rather than locally. 25 Such techniques usually have difficulty in avoiding edge effects, which give undesired vortex entry due to the enhanced currents and defects along the etched edges, 16 and do not reveal the local intrinsic nonlinear properties of superconductors.…”

Spatially-resolved nonlinearity measurements of YBa2Cu3O7−δ bicrystal grain boundaries

“…In addition, most existing experimental techniques focus on 3rd order nonlinearities, which can be conveniently studied by intermodulation techniques, but rarely address the 2nd order nonlinear response. Here we present a technique to locally characterize 2nd and 3rd order nonlinearities through spatially localized harmonic generation.In prior work, [9] we studied the intermodulation signal from a high-T c superconducting microwave resonator * Electronic address: sycamore@wam.umd.edu † Electronic address: anlage@squid.umd.edu using a scanned electric field pick-up probe. Both the "global" and the "local" intermodulation power measured with the open-end coaxial probe were presented.…”

“…In prior work, [9] we studied the intermodulation signal from a high-T c superconducting microwave resonator * Electronic address: sycamore@wam.umd.edu † Electronic address: anlage@squid.umd.edu using a scanned electric field pick-up probe. Both the "global" and the "local" intermodulation power measured with the open-end coaxial probe were presented.…”

“…Fy, 74.25.Nf, 74.62.Dh, 74.72.Bk The nonlinear properties of high-T c superconductors have been of great concern in microwave applications, although the microscopic origins of the nonlinear response still remain uncertain. [7] Many experiments have studied the intermodulation power, [8,9] harmonic generation, [10,11] or the nonlinear surface impedance of superconductors [12,13] as a function of applied microwave power. However, most nonlinear experiments are done with resonant techniques, which by their nature study the averaged nonlinear response from the whole sample rather than locally.…”

Study of local nonlinear properties using a near-field microwave microscope

“…Many experiments have studied the nonlinearity of superconductors in terms of intermodulation distortion [5], [6], harmonic generation [7], [8], or the nonlinear surface impedance [9]- [11]. However, most of these experiments are done with resonant techniques, which by their nature study the averaged nonlinear response from the sample rather than locally, hence have difficulty in either avoiding edge effects, or determining the homogeneity, in terms of nonlinearities, of the sample.…”