Terahertz metamaterial with asymmetric transmission

TL;DR

This paper demonstrates that a planar, asymmetric metamaterial can exhibit asymmetric transmission of terahertz radiation, enabled by lossy, low-symmetry chiral structures that excite enantiomerically sensitive plasmons, with potential applications in negative index and slow light devices.

Contribution

First experimental demonstration of asymmetric terahertz transmission in a planar, asymmetric metamaterial with chiral properties, linking it to enantiomerically sensitive plasmon excitation.

Findings

Asymmetric transmission observed in 0.25-2.5 THz range.

Linked asymmetric transmission to excitation of enantiomerically sensitive plasmons.

Identified bands with positive, negative, and zero phase/group velocities.

Abstract

We show for the first time that a planar metamaterial, an array of coupled metal split-ring resonators with a unit cell lacking mirror symmetry, exhibits asymmetric transmission of terahertz radiation (0.25-2.5 THz) propagating through it in opposite directions. This intriguing effect, that is compatible with Lorentz reciprocity and time-reversal, depends on a directional difference in conversion efficiency of the incident circularly polarized wave into one of opposite handedness, that is only possible in lossy low-symmetry planar chiral metamaterials. We show that asymmetric transmission is linked to excitation of enantiomerically sensitive plasmons, these are induced charge-field excitations that depend on the mutual handedness of incident wave and metamaterial pattern. Various bands of positive, negative and zero phase and group velocities have been identified indicating the opportunity to develop polarization sensitive negative index and slow light media based on such metamaterials.