Tunable plasmons in black phosphorus-coated nanowire waveguides

Abstract The unique atomic-puckering crystal structure of layered black phosphorus gives rise to pronounced in-plane anisotropy. As a result, it is essential to consider this property when considering plasmon waveguides with black phosphors. In this work, surface plasmons in armchair (AC-) and zigzag (ZZ-) type black phosphorus coated nanowires (BPCNWs) are exhibited and analyzed in the infrared range. The common mode cutoff condition are found to be only applicable in ZZ-BPCNWs, while the cut-off frequencies in AC-BPCNWs are restricted by the conservation of energy due to the in-plane anisotropy of black phosphorus. Moreover, increasing the electrical doping, reducing the radius and permittivity of nanowire are beneficial to realize single mode regime without sacrificing the propagation length. The proposed model provides a fast insight into the mode behavior of cylindrical anisotropic 2D materials, which would be useful for applications based on cylindrical plasmonic waveguides with anisotropic 2D materials.