Composite metamaterials with dual-band magnetic resonances in the terahertz frequency regime

Composite metamaterials(CMMs) combining a subwavelength metallic hole array (i.e. one-layer fishnet structure) and an array of split-ring resonators(SRRs) on the same board are fabricated with gold films on silicon wafer. Transmission measurements of the CMMs in the terahertz range have been performed. Dual-band magnetic resonances, namely, a LC resonance at 4.40 THz and an additional magnetic resonance at 8.64 THz originating from the antiparallel current in wire pairs in the CMMs are observed when the electrical field polarization of the incident light is parallel to the gap of the component SRR. The numerical simulations agree well with the experimental results and further clarify the nature of the dual-band magnetic resonances.Comment: 4 figures, 14 page

Electronic correlations and energy gap in the bilayer nickelate La3_{3}Ni2_{2}O7_{7}

The discovery of superconductivity with a critical temperature of 80~K in La$_{3}$Ni$_{2}$O$_{7}$ under pressure has received enormous attention. La$_{3}$Ni$_{2}$O$_{7}$ is not superconducting under ambient pressure but exhibits a density-wave-like transition at $T^{\ast} \simeq 115$~K. Understanding the electronic correlations, charge dynamics and dominant orbitals are important steps towards the mechanism of superconductivity and other instabilities. Here, our optical study shows that La$_{3}$Ni$_{2}$O$_{7}$ features strong electronic correlations which significantly reduce the electron's kinetic energy and place it in the proximity of the Mott phase. The low-frequency optical conductivity reveals two Drude components arising from multiple bands dominated by the Ni-$d_{x^2 - y^2}$ and Ni-$d_{3z^2 - r^2}$ orbitals at the Fermi level. Above $T^{\ast}$, the scattering rates for both Drude components vary linearly with temperature, indicating non-Fermi-liquid behavior which may be associated with spin-fluctuation scattering. Below $T^{\ast}$, a gap opens in the Ni-$d_{3z^2 - r^2}$ orbital, suggesting the importance of the Ni-$d_{3z^2 - r^2}$ orbital in the density-wave-like instability. Our experimental results provide key insights into the mechanism of the density-wave-like order and superconductivity in La$_{3}$Ni$_{2}$O$_{7}$.Comment: 26 pages, 4 figures, Comments are welcome and appreciate