Superconducting RF Metamaterials Made with Magnetically Active Planar Spirals

TL;DR

This paper presents superconducting RF metamaterials made with planar Nb spirals that exhibit high quality factors, tunable magnetic responses, and nonlinear effects at low frequencies, enabling compact and efficient designs.

Contribution

The study introduces a novel superconducting metamaterial design using planar Nb spirals with high Q-factors and tunable magnetic properties, advancing low-frequency metamaterial applications.

Findings

High loaded quality factor (Q) in RF metamaterials

Tunable magnetic response via temperature and magnetic field

Observation of nonlinearity and meta-stable jumps

Abstract

Superconducting metamaterials combine the advantages of low-loss, large inductance (with the addition of kinetic inductance), and extreme tunability compared to their normal metal counterparts. Therefore, they allow realization of compact designs operating at low frequencies. We have recently developed radio frequency (RF) metamaterials with a high loaded quality factor and an electrical size as small as $\sim$$\lambda$658, ($\lambda$ is the free space wavelength) by using Nb thin films. The RF metamaterial is composed of truly planar spirals patterned with lithographic techniques. Linear transmission characteristics of these metamaterials show robust Lorentzian resonant peaks in the sub- 100 MHz frequency range below the $T_c$ of Nb. Though Nb is a non-magnetic material, the circulating currents in the spirals generated by RF signals produce a strong magnetic response, which can be tuned sensitively either by temperature or magnetic field thanks to the superconducting nature of the design. We have also observed strong nonlinearity and meta-stable jumps in the transmission data with increasing RF input power until the Nb is driven into the normal state. We discuss the factors modifying the induced magnetic response from single and 1-D arrays of spirals in the light of numerical simulations.