We introduce here a parity-time-($\mathcal{P}\mathcal{T}$) symmetric system using an optically pumped, active graphene metasurface paired with a resistive metallic filament, realizing a unidirectional reflectionless propagation of terahertz (THz) waves. The amplified THz stimulated emission and tailored plasmon resonances in the graphene metasurface may achieve an equivalent negative-resistance converter at THz frequencies. We theoretically demonstrate that the combination of the spectral singularity in a $\mathcal{P}\mathcal{T}$-symmetric system and the chemical sensitivity of graphene may give rise to exotic scattering responses, strongly influenced by the presence of charged impurities in graphene at the spontaneous $\mathcal{P}\mathcal{T}$-symmetry-breaking point. This graphene-based $\mathcal{P}\mathcal{T}$-symmetric device may have broad relevance beyond the extraordinary manipulation of THz waves, as it may also open exciting prospects for detecting gas, chemical, and biological agents with high sensitivities.

• Received 3 April 2016

DOI:https://doi.org/10.1103/PhysRevApplied.5.064018

© 2016 American Physical Society

Condensed Matter & Materials Physics

Source: https://link.aps.org/doi/10.1103/PhysRevApplied.5.064018