Superradiantly limited linewidth in complementary THz metamaterials on Si-membranes

TL;DR

This study investigates superradiant effects in THz metamaterials on silicon membranes, demonstrating linewidth narrowing and collective decay behavior, with implications for designing high-Q resonators at THz frequencies.

Contribution

The paper reveals how superradiant broadening can be controlled in THz metamaterials on Si membranes, highlighting the role of substrate and resonator spacing in linewidth tuning.

Findings

Linewidths of resonator modes narrow with increased spacing.

Decay rate of LC mode depends linearly on resonator density.

Metamaterials can be engineered for low superradiant broadening.

Abstract

We study complementary double split ring THz resonators fabricated on a 10 mum thin Si-membrane. The linewidths of the fundamental LC-mode and dipolar mode are drastically narrowing with increased resonator spacing. The extracted decay rate of the LC-mode as a function of the resonator density shows a linear dependence, evidencing a collective superradiant effect of the resonator array. Furthermore, we show that a metamaterial can be designed for a low superradiant broadening of the resonance at high resonator densities, i.e. in the metamaterial condition. The use of a thin membrane as a substrate is crucial, since it shifts the THz surface plasmon polaritons modes to much higher frequencies, preventing them to couple to the LC mode and unveiling the superradiant broadening mechanism for a large range of lattice spacings. At higher frequencies, not interfering with the high Q LC-mode, other additional modes, which we ascribe to photonic crystal modes, form in the Si-membrane. We map the angle dependent band structure and show corresponding simulated electric field distributions.