Kharkiv Quantum Seminar: 2023 November 21, 16:00 (EET)

Laser Scanning Microscopy of Superconducting Microwave Devices –

Collaborative Discoveries

Steven M. Anlage (Quantum Materials Center, Physics Department, University of Maryland, USA)

I have been very fortunate to collaborate with Dr. A. P. Zhuravel of the Institute of Low Temperature Physics and Engineering (NASU) in Kharkiv, Ukraine on laser scanning microscopy of superconducting microwave devices. Together we have enjoyed a fruitful collaboration spanning parts of two centuries, and we have discovered many fascinating phenomena. We have developed and refined a microwave microscope that can image the distribution of RF currents in resonant microwave devices, and metamaterials. We have imaged current distributions at the edges of patterned thin films and observe large enhancements of current density at these edges. We have also imaged the anisotropic nonlinear Meissner effect in cuprate superconductors, providing a real-space image of the direction-dependent superconducting energy gap on the Fermi surface. Later, we demonstrated the power of this microscope by examining the microscopic properties of RF SQUID metamaterials. The SQUID metamaterials have a collective resonant response between 10 and 20 GHz, tuned by very small dc magnetic fields. Through RF current imaging we find that the SQUIDs do not all oscillate in phase while being tuned, but break in to domains with different resonant frequencies. Learning how to tame this disorder through machine learning and in-situ modification of the metamaterial is an ongoing effort, inspired by our collaboration.

Acknowledgement: This work is funded by US Department of Energy through grant # DE-SC0017931, the US National Science Foundation through grant # DMR-2004386, and the Maryland Quantum Materials Center.