Tunability of Superconducting Metamaterials

TL;DR

This paper explores three superconducting methods—temperature, dc magnetic field, and rf magnetic field—to tune the electromagnetic response of metamaterials, demonstrating experimental results with superconducting split-ring resonators.

Contribution

It introduces three novel superconducting tuning techniques for metamaterials, with experimental validation and analysis of their effects on resonator properties.

Findings

Dc magnetic field tuning is hysteretic in frequency.

Rf magnetic field tuning suppresses the quality factor at high power.

Magneto-optical imaging shows inhomogeneous vortex entry during dc tuning.

Abstract

Metamaterials are artificial structures with unique electromagnetic properties, such as relative dielectric permittivity and magnetic permeability with values less than 1, or even negative. Because these properties are so sensitive to loss, we have developed metamaterials comprised of superconducting waveguides, wires, and split-ring resonators. An important requirement for applications of these metamaterials is the ability to tune the frequency at which the unique electromagnetic response occurs. In this paper we present three methods (unique to superconductors) to accomplish this tuning: temperature, dc magnetic field, and rf magnetic field. Data are shown for dc and rf magnetic field tuning of a single Nb split-ring resonator (SRR). It was found that the dc field tuning was hysteritic in the resonant frequency data, while the quality factor, $Q$, was less hystertic. The rf power tuning showed no hysteresis, but did show supression of the $Q$ at high power. Magneto-optical images reveal inhomogeneous magnetic vortex entry in the dc field tuning, and laser scanning photoresponse images for a YBa$_2$Cu$_3$O$_{7-\delta}$ SRR reveals the current distribution in the rings.