Polarization independent and non-reciprocal absorption in multi-layer anisotropic black phosphorus metamaterials

The polarization independent and non-reciprocal absorption is particularly crucial for the realization of non-reciprocal absorption devices. Herein, we proposed and studied the absorption response of two- and three-layer anisotropic black phosphorus (BP) metamaterials by using the finite-difference time-domain (FDTD) simulation and radiation oscillator theory (ROT) analysis. It is shown that, due to unequal surface plasmon resonant modes excited in zigzag (ZZ) and armchair (AC) directions of the anisotropic BP layer, tunable polarization independent and dependent absorption can be achieved for the proposed multi-layer anisotropic BP metamaterials with AC-AC, AC-ZZ, ZZ-AC, AC-AC-φ, AC-ZZ-φ, and ZZ-AC-φ configurations. Especially, the polarization independent absorption also can be realized for odd-layer BP nanostructures. Unlike previous reports, polarization independence only can be achieved in the even-layer BP nanostructure. Moreover, tunable non-reciprocal absorption with the extremely large non-reciprocal degree (NRD) is also found in the case of AC-ZZ and ZZ-AC configurations and AC-ZZ-φ and ZZ-AC-φ configurations. These results may open up the possibility of realizing tunable polarization independent and non-reciprocal plasmonic devices based on 2D materials.