MAGNETOPLASMA OSCILLATIONS IN NANOSCALE TUBULES WITH HELICAL SYMMETRY

The collective excitations associated with density fluctuations of a s ystem of electrons on nanoscale tubules when a constant magnetic field is present along the tube axes are presented. Several types of acoust ic and optical magnetoplasma modes are found. The Kohn anomalies assoc iated with the static density response for appropriate particle-hole e xcitations across the Fermi surface are also discussed. When the spin- paramagnetic contribution is ignored, it is found that the Fermi energ y, magnetization, magnetic susceptibility, and the collective properti es are periodic in the magnetic flux enclosed by the cylinder. For the se to be relevant to graphitic tubules, which are thought to be obtain ed by rolling two-dimensional graphite sheets into cylinders, their in herent helical structures must be incorporated into the theory. It is shown that a transformation of the cylindrical wave states to helical wave states allows these results to be made relevant to nanoscale tubu les with helical symmetry.