Applications and perspective of near-field microwave microscope in high-throughput characterizations of superconducting materials

Abstract

High- T c superconductors are promising in applications of power transmission, magnetic levitation, magnetic resonance imaging and other fields which are limited so far by the low critical temperature of present materials, so searching for superconducting materials with higher T c is of much significance. However, in the process of exploring new materials and establishing a complete phase diagram, a new route of high efficiency and accuracy is highly desired. Fortunately, the materials genome initiative (MGI) composed of calculations and data processing, high-throughput synthesis and fast screening technologies has been showing great advantages in shortening the R&D cycle and saving the cost. For example, in our recent work, the continuous-composition-spread La2− x Ce x CuO4 films synthesized by the third-generation com- binatorial film technique enable us to be closer to the quantum critical point in cuprate superconductors and the T c-continuous-variation FeSe film is helpful to track the superconductivity in the iron-based family. As the indispensable experimental component, the high-throughput synthesis and screening techniques play the key role in the MGI. In this review, we briefly introduce the commonly used combinatorial film synthesizing technologies as well as several rapid characterization techniques such as micro-area X-ray diffractometer, imaging ellipsometer and laser thermal characterization techniques. The common features for the high-throughput characterization methods are pointed out that the ″sharp tip″ which can scan on the sample surface or the probe array is necessary. The spatial resolution of the facility is determined by the dimension of the tip or the resolution of the virtual ″tip″. According to these clues, near-field microwave microscope (NMM) of high resolution and nondestructive scanning, a typical high-throughput electromagnetic characterization method, is beneficial for characterizing combinatorial superconducting films since the surface impedance of superconductors is related to the magnetic penetration depth which can reflect the feature of superconducting gap. Thus, taking the developing history of NMM as a starting point, we summarize its working principle, instrumental configuration including near-field microwave probe, distance-control component, microwave generation and detection circuit, as well as commonly used analysis methods, such as lumped element model and cavity perturbation theory. Then the design concept and theory support of evanescent microwave probe (EMP) are explained in detail as an example of NMM. Two prototypes about superconductors of EMP studies are also demonstrated. Finally, some potential applications of NMM in the high-throughput characterization of combinatorial superconducting films have been prospected. We expect that the NMM will play a more important role in disclosing the nature of pseudo gap and the vortex dynamics.