Magnetic control of Rashba splittings in symmetric InAs quantum wells

We propose a mechanism to control the Rashba-induced subband splitting by a magnetic field using a symmetric double quantum well (QW) system, where the lowest two subbands are coupled by a position-dependent Rashba parameter α(z). In such a system, all subbands are spin degenerate due to the time reversal symmetry and the spatial inversion symmetry at zero magnetic field, despite the presence of the Rashba spin-orbit interaction. Applying an external magnetic field parallel to the QW plane (B∥y^) lifts this spin degeneracy breaking the time reversal symmetry, where the spin splitting energies are controllable in the range between zero and 2.9 meV, the latter being on the same order of magnitude as a typical Rashba splitting in a narrow asymmetric QW. We find that the first and second subband energy levels for a selected spin state with k∥=(kF,0,0) anticross each other, and that the energy of the subband splitting Δ0, equivalent to the Rashba splitting for the case of single QWs, can be determined from the value of the anticrossing magnetic field Bac. These results suggest that the investigation in the symmetric double QWs would provide useful approaches for quantitative understanding of the Rashba spin-orbit interaction.