Optical properties of a spherical electron gas in the presence of a uniform magnetic field

We calculate the plasmon frequencies of an electron gas on a two-dimensional spherical surface within the framework of RPA (random phase approximation) when a weak uniform magnetic field is applied on the sphere. We show that a coupling between different angular momentum numbers in the excitation process takes place due to the existence of the magnetic field. We investigate how the plasmon energies vary as a function of the density of electrons on the sphere with and without the magnetic field. We also show that an electron Wigner lattice on a two-dimensional spherical surface can be regarded as a nanoshell with infinitesimal thickness by comparing the plasmon dispersion relation in former case with the semiclassical equation for nanoshells in zero magnetic field. Further issues regarding the finite thickness are discussed.