Imaging microwave response of rf-SQUID metasurface in dc magnetic field

We report direct visualization of spatially localized excitations in an array of 27×27 coupled rf-SQUIDs forming a magnetic meta-surface for electromagnetic wave propagation. The technique of low-temperature Laser Scanning Microscopy (LSM) is applied to investigate contributions of individual meta-atoms to the macroscopic dc flux tuned microwave response in the high rf flux limit. The obtained LSM images of the RF current distributions across the SQUID array at zero dc flux confirms a high degree of coherence of the entire meta-surface assuming radially anisotropic nearest neighbor coupling in 2D arrays of rf-SQUIDs. We also find a rich variety of spatially clustered stable dissipative states of the rf-SQUID array due to the non-uniform penetration of magnetic flux in the direction perpendicular to the uniform external magnetic field. Our measurements show that the LSM technique is a powerful tool for spatially-resolved characterization of complicated meta-materials and may be useful for their optimization.