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.