Tunable natural terahertz and mid-infrared hyperbolic plasmons in carbon phosphide

Abstract

Hyperbolic polaritons in ultra thin materials such as few layers of van der Waals heterostructures provide a unique control over light-matter interaction at the nanoscale and with various applications in flat optics. Natural hyperbolic surface plasmons have been observed on thin films of WTe2 in the light wavelength range of 16–23 μm (≃13–18 THz) [Nat. Commun. 11, 1158 (2020)]. Using time-dependent density functional theory, it is found that carbon doped monolayer phosphorene (β-allotrope of carbon phosphide monolayer) exhibits natural hyperbolic plasmons at frequencies above ≃5 THz which is not observed in its parent materials, i.e. monolayer of black phosphorous and graphene. Furthermore, we found that by electrostatic doping the plasmonic frequency range can be extended to the mid-infrared.