Ground state and far-infrared absorption of two-electron rings in a magnetic field

Motivated by recent experiments [A. Lorke {\em et al.}, Phys. Rev. Lett.\ {\bf 84}, 2223 (2000)] an analysis of the ground state and far-infrared absorption of two electrons confined in a quantum ring is presented. The height of the repulsive central barrier in the confining potential is shown to influence in an important way the ring properties. The experiments are best explained assuming the presence of both high- and low-barrier quantum rings in the sample. The formation of a two-electron Wigner molecule in certain cases is discussed.