Electronic Excitations in Cylinder Superlattices

A cylinder superlattice is formed by arranging the same hollow tubules in a linear lattice. Excitation properties are studied by evaluating the dielectric function within the linear-response approximation. The electronic excitations of a cylinder superlattice are the superposition of those of the individual tubules. However, these two systems an very different from each other. The excitations of different transferred angular momenta (L's) are generally coupled in the former, while they are decoupled in the latter. A cylinder superlattice has a highly anisotropic structure, so the electronic excitations strongly depend on the magnitude (q) and the direction (θ) of the transferred momentum. It might exhibit two plasmon branches. The low- and high-frequency plasmons, respectively, come from the L = 0 and L = 1 collective excitations in all tubules. Whether they could exist is determined by q and θ. The comparison among multi-cylinder systems, cylinder superlattices, and cylinder bundles shows that they, respectively, exhibit one-, two-, and three-dimensional characteristics in the collective excitations, e.g., the q-dependence of the plasmon frequency. This important difference is caused by the different Coulomb interactions.