Black Phosphorus Carbide as a Tunable Anisotropic Plasmonic Metasurface

Tailoring photonics for monolithic integration beyond the diffraction limit opens a new era of nanoscale electronic-photonic systems, including graphene plasmonics which exhibits low level of losses and high degree of spatial confinement. Limited to its isotropic optical conductivity, searching for new plasmonic building blocks which offer tunability and design flexibility beyond graphene is becoming quite crucial for next-generation optoelectronic device. Here, motivated by the recent emergence of a new 2D material, we develop a mid-infrared (mid-IR) metasurface by nanostructuring a thin layer of black phosphorus carbide (b-PC) and realize efficient excitation of hybrid plasmon mode at deep subwavelength-scale. Far-field infrared spectroscopy demonstrates that the hybrid plasmon mode displays an anticrossing behavior of two splitting optical modes, which can be attributed to the Fano resonance between plasmons and IR-active optical phonons in b-PC. Significantly, it further presents a strong anisotropic behavior along different crystal orientations, which arises from its peculiar puckered lattice structure with two clearly distinguishable axes. The results illustrate that anisotropic b-PC plasmon not only represents an important advance in subwavelength optoelectronics, but also provides a viable platform for hyperbolic metamaterials, bringing widespread applications into biosensors, single-photon source, nanoantenna, and subwavelength resolution imaging.