Dielectric response of cylindrical nanostructures in a magnetic field

We study the magnetic field dependence of the dielectric response of large cylindrical molecules such as nanotubes. When a field-induced level crossin g takes place, an applied electric field has two effects: it may cause a. l inear instead of the usual quadratic Stark effect or the difference in the quadratic Stark coefficient of the two levels leads to a discontinuity in t he polarization. Explicit calculations are performed for doped nanotubes an d a rich structure in the real part of the low-frequency dielectric functio n epsilon'(H) is found when a magnetic field is applied along the cylinder axis. It is suggested that studies of epsilon'(H, T) can serve as a spectro scopic tool for the investigation of large ring-shaped or cylindrical molec ules.