ELEMENTARY EXCITATIONS IN CYLINDER BUNDLES

Elementary excitations in a cylinder bundle, which is formed by packin g the same hollow tubules into a two-dimensional triangular lattice, a re studied. The dielectric response function is calculated within the linear response approximation. The electronic excitations of the cylin der bundle are the superposition of those of all tubules. Due to the i ntertube Coulomb interactions, their characteristics quite differ from those of an isolated tubule. The plasmon, which corresponds to the co herent oscillations of all carriers, could exhibit a prominent peak in excitation spectrum. The excitation properties strongly depend on the tubular radius, the effective electron mass, and the magnitude and th e direction of the momentum transfer (q). At small momentum, there exi sts a simple relation between excitation properties and polar angles ( theta's). Both intensity of excitation spectrum and plasmon frequency decrease as theta increases. The collective plasma oscillations parall el and perpendicular to the tubular axis contrast sharply with each ot her, which clearly illustrates the anisotropic behavior. The ratio bet ween these two plasmon frequencies is found to be smaller than root 2.