Microwave Current Imaging in Passive HTS Components by Low-Temperature Laser Scanning Microscopy (LTLSM)

Abstract

distributed parameters in SC films as a function of the local critical current [27]. It is possible to manifest local resistive characterization of the SC transition [28][29][30], the spatial variations of magnetic and electromagnetic fields [31][32][33][34], and to carry out 2-D defectoscopy of structural and technological faults in operating SC devices and circuits [35][36][37]. In this work, we apply the LTLSM technique to analyze the redistribution of rf current flow in the vicinity of typical microdefects in YBCO films leading to anomalously high rf photoresponse, and possibly to nonlinear microwave behavior of SC devices. We have used the LTLSM technique for a spatially resolved investigation of the microwave transport properties, nonlinearities and material inhomogeneities in an operating coplanar waveguide YBa2Cu3O7-d (YBCO) microwave resonator on an LaAlO3 (LAO) substrate. The influence of twin-domain blocks, inplane rotated grains, and micro-cracks in the YBCO film on the nonuniform rf current distribution were measured with a micrometer-scale spatial resolution. The impact of the peaked edge currents and rf field penetration into weak links on the linear device performance were studied as well. The LTLSM capabilities and its future potential for non-destructive characterization of the microwave properties of superconducting circuits are discussed

Realization and Modeling of Metamaterials Made of rf Superconducting Quantum-Interference Devices

“…A dc magnetic field was shown to add magnetic flux to a thin-film Nb SRR, increasing its inductance and loss [40]. The rf magnetic field created enhanced rf screening currents at discrete locations in the SRR, resulting in enhanced inductance and dissipation as magnetic flux moved into and out of the superconducting film at high frequency [40,[42][43][44][45][46]. It was also found that a superconducting resonator exhibiting an analogue of electromagnetically induced transparency showed a strong switching behavior at high excitation power [36], for similar reasons.…”

Imaging of Microscopic Sources of Resistive and Reactive Nonlinearities in Superconducting Microwave Devices

“…The power of the laser P L =10μW was fixed low enough to introduce minimal perturbation on the global microwave properties of the resonator. The intensity of the laser is modulated at a frequency of f M =100 kHz, producing an oscillating thermal probe of about 4 μm in diameter [3,4,6,7]. Transmitted HF signals are amplified and measured by a spectrum analyzer, as shown in Fig.2.…”

“…Alexander P. We have shown earlier that the low-temperature Laser Scanning Microscope (LSM) is a powerful nondestructive evaluation technique for non-contact, spatially-resolved probing of the local HF current density, J HF (x,y) in HTS films and devices [3]. This LSM method was applied next for mapping optical, thermal, HF and dc electron transport properties and superconducting critical parameters of HTS samples directly in their operating state at T < T c , with micronscale spatial resolution [4].…”

Imaging collective behavior in an rf-SQUID metamaterial tuned by DC and RF magnetic fields

“…Note that the LSM photoresponse is a linear function of laser power up to ∼ 100 µW of absorbed laser power when the critical state of the Josephson junction is achieved by overheating by laser. Temperature modulation estimates for LSM measurements have been published before in references [52][53][54][55]…”