Spin–orbit effects on two-electron states in nanowhisker double quantum dots

We investigate theoretically the combined effects of the electron–electron and the Rashba spin–orbit interactions on two electrons confined in quasi-one-dimensional semiconductor double quantum dots. We study both InSb-based structures, which are of interest due to their strong spin–orbit coupling, and also InAs-based systems, which have been recently studied experimentally. We calculate the two-electron wave functions in the effective-mass approximation and explore the interplay between the two interactions on the energy levels and the spin of the states. The energy spectrum as a function of an applied magnetic field shows crossings and anticrossings between triplet and singlet states, associated with level mixing induced by the spin–orbit coupling. We find that the fields at which these crossings occur can be naturally controlled by the interdot barrier width, which controls the exchange integral in the structure.