Anisotropic Plasmon Dispersion and Damping in Multilayer 8-Pmmn Borophene Structures

We investigate the collective plasma oscillations theoretically in multilayer 8-Pmmn borophene structures,where the tilted Dirac electrons in spatially separated layers are coupled via the Coulomb interaction.We calculate the energy disper-sions and Landau dampings of the multilayer plasmon excitations as a function of the total number of layers,the interlayer separation,and the different orientations.Like multilayer graphene,the plasmon spectrum in multilayer borophene consists of one in-phase optical mode and N-1 out-of-phase acoustical modes.We show that the plasmon modes possess kinks at the boundary of the interband single-particle continuum and the apparent anisotropic behavior.All the plasmon modes ap-proach the same dispersion at a sufficiently large interlayer spacing in the short-wavelength limit.Especially along specific orientations,the optical mode could touch an energy maximum in the nondamping region,which shows non-monotonous behavior.Our work provides an understanding of the multilayer borophene plasmon and may pave the way for multilayer borophene-based plasmonic devices.