Far-infrared excitations in an antidot at finite magnetic fields

We have investigated the far-infrared dipole modes of an antidot submitted to a perpendicularly applied magnetic field B. The ground state of the anti dot is described in local spin-density functional theory, and the spectrum in time-dependent local spin-density functional theory. The results are com pared with those corresponding to a quantum dot of similar electronic surfa ce density. The method is able to reproduce two of the more salient experim ental features, namely,that the main bulk and edge modes have the same circ ular polarization, and that the negative B dispersion edge branch oscillate s, with minima at the B values corresponding to fully occupied Landau level s. It fails, however, to achieve the unique feature of short-period antidot lattices that the energy of the edge magnetoplasmon approaches the cyclotr on frequency for small B values. The existence of anticyclotron-polarized b ulk modes is discussed, and a detailed account of the dipole spin mode is p resented.