Laser Scanning Microscopy to Interrogate Electromagnetic Responses of Superconducting Microwave Devices

Laser scanning microscopy (LSM) with its micron-scale resolution and millimeter-wide field of view has been employed to image the rf current distributions in superconducting devices and resonators [1-3]. In this work, we imaged the electromagnetic (EM) field distribution of two samples: a new generation of radio frequency superconducting quantum interference device (rf SQUID) metamaterials made up of strongly capacitively and inductively coupled rf SQUIDs [4], and a chip of frequency-multiplexed coplanar waveguide (CPW) resonators. We have visualized the modes dominated by the overlap capacitors in the capacitively-coupled stacked SQUID metamaterial as opposed to those dominated by the Josephson junctions in conventional SQUID metamaterials [2]. A new photoresponse mechanism arising from photo-induced charge carriers in the semiconducting dielectric gaps has been observed in the CPW resonators. These results demonstrate the ability of the LSM to investigate the EM field distribution in superconducting electronics.

We thank Robin Cantor of Star Cryoelectronics for help with the design and fabrication of the rf SQUID metamaterials in this work.

[1] Low Temp. Phys 32, 6 (2006) https://doi.org/10.1063/1.2215376

[2] Appl. Phys. Lett. 114, 082601 (2019) https://doi.org/10.1063/1.5064658

[3] Phys. Rev. Lett. 110, 087002 (2013) https://doi.org/10.1103/PhysRevLett.110.087002

[4] Supercond. Sci. Technol. 37, 075023 (2024) https://doi.org/10.1088/1361-6668/ad54f8