Third-order intermodulation is studied in two-pole X-band high-temperature superconducting (HTS) HgBa2CaCu2O6+δ microstrip filters at >77K. The third-order intercept (IP3) of the HgBa2CaCu2O6+δ filters is consistently higher than that of the YBa2Cu3O7 filter of the same geometry in this temperature range. At 110K, the IP3 of 38dBm remains for the Hg-1212 filters, the best so far achieved at T>100K. The dc critical current density Jc and the rf one JIP3 derived from the IP3 have a similar reduced temperature dependence, suggesting that the magnetic vortex depinning in HTS materials dominates the microwave nonlinearity at elevated temperatures.

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A near-field scanning microwave microprobe (NSMM) has been integrated with electrical current-voltage (I–V) characterization for mapping electrical current density (J) in conducting films at room temperature (RT). In this technique, the focused microwave emitted at the tip of the NSMM was used to alter the local resistance of the sample via heating which results in a voltage response ΔV that depends linearly on the local J and the applied microwave power. In addition to the ΔV map generated during the NSMM scan over a sample, a microwave response map can be recorded simultaneously using the NSMM, providing complementary information of sample morphology and surface impedance. On silver microbridges with predefined patterns, a 10-μm spatial resolution has been demonstrated and better resolution may be achieved with further optimization. Hence, this technique provides a simple and nondestructive method for identification of current-limiting defects in conducting films and may be scaled for reel-to-reel quality control of the high-Tc superconductor coated conductors at RT.

A dual-channel scanning microprobe ͑dual probe͒ has been developed for simultaneous mapping of microwave and optical properties of a sample. It employs a tunable open-ended coaxial resonator with a tapered and metal-coated fiber optic tip, from which microwave and light can be emitted/ collected simultaneously. The microwave channel of this probe, operating at 1.5 GHz, can detect changes in sheet resistance (R x ) above 293 m⍀ with a spatial resolution ranging from 5 to 10 m. The optical channel, on the other hand, has a spatial resolution ϳ1 m. The poorer spatial resolution in the microwave channel was attributed to its lower sensitivity. Imaging of dielectric grid and high-T c superconducting microwave resonators was carried out at ambient temperature.

Identification of defects that obstruct electrical current in high-temperature superconductors (HTS) is of great importance for applications. A technique that combines near-field scanning microwave microscopy (NSMM) with transport measurement was developed to obtain multiple sets of complementary maps on the same sample area. This technique takes advantage of the NSMM's unique capability to function both as an EM wave emitter that can locally heat a spot on a current-biased sample and also as a detector to map the spatial non-uniformity in electromagnetic properties of the sample including loss, dielectric constant, and surface morphology. Macroscopic defects in YBa 2 Cu 3 O 7 (YBCO) films were clearly identified and imaged using this technique with adequate sensitivity and resolution.