Singlet-triplet transition of a two-electron quantum ring in magnetic and electric fields

We present an exact numerical calculation of the spin phase diagram of a two-electron quantum ring as a function of an applied in-plane electric field E and a perpendicular magnetic field B. In general, large E and B favour, respectively, singlet and triplet states. At low fields, however, the spin phase diagram shows singlet-triplet oscillations and the formation of spin islands surrounded by the complementary phase. Calculations of the density dipole excitation spectrum as a function of the electric field are also reported. (c) 2007 Elsevier B.V All rights reserved.