E. L. Ivchenko

Experimental Separation of Rashba and Dresselhaus Spin Splittings in Semiconductor Quantum Wells

The relative strengths of Rashba and Dresselhaus terms describing the spin-orbit coupling in semiconductor quantum well (QW) structures are extracted from photocurrent measurements on n-type InAs QWs containing a two-dimensional electron gas (2DEG). This novel technique makes use of the angular distribution of the spin-galvanic effect at certain directions of spin orientation in the plane of a QW. The ratio of the relevant Rashba and Dresselhaus coefficients can be deduced directly from experiment and does not relay on theoretically obtained quantities. Thus our experiments open a new way to determine the different contributions to spin-orbit coupling.

Electronic g factor in biased quantum wells

A theory of the Zeeman splitting of electronic spin states in biased quantum-well structures has been developed. The g factor tensor has been calculated as a function of the applied electric field and the well width. The longitudinal g factor has been shown to be more sensitive to the field than the transverse, or in-plane, component. For a fixed electric field and increasing the well width, the g factor components saturate towards the corresponding values for a single heterojunction. The theoretical results has been compared with available experimental data.

Precession spin relaxation mechanism caused by frequent electron-electron collisions

It is shown that the D’yakonov-Perel’ spin relaxation mechanism in a two-dimensional electron gas is controlled not only by the electron-momentum relaxation that accounts for the electron mobility but also by the electron-electron collisions. The kinetic equation describing the mixing of electron spin in the k space was solved, and the spin relaxation time τs caused by frequent electron-electron collisions was determined. The time τ s was calculated for a nondegenerate electron gas both with and without allowance for the exchange interaction.

Circular photogalvanic effect induced by monopolar spin orientation in p-GaAs/AlGaAs multiple-quantum wells

The circular photogalvanic effect (CPGE) has been observed in (100)-oriented p-GaAs/AlGaAs quantum wells at normal incidence of far-infrared radiation. It is shown that monopolar optical spin orientation of free carriers causes an electric current which reverses its direction upon changing from left to right circularly polarized radiation. CPGE at normal incidence and the occurrence of the linear photogalvanic effect indicate a reduced point symmetry of studied multilayered heterostructures. As proposed, CPGE can be utilized to investigate separately spin polarization of electrons and holes and the symmetry of quantum wells.

Spin coherence of a two-dimensional electron gas induced by resonant excitation of trions and excitons in Cd Te ∕ ( Cd , Mg ) Te quantum wells

The mechanisms for generation of long-lived spin coherence in a two-dimensional electron gas (2DEG) have been studied experimentally by means of a picosecond pump-probe Kerr rotation technique.

Resonant inversion of the circular photogalvanic effect in n-doped quantum wells

\mathrm{Cd}\mathrm{Te}∕(\mathrm{Cd},\mathrm{Mg})\mathrm{Te}

Spin and valley-orbit splittings in Si Ge ∕ Si heterostructures

quantum wells with a diluted 2DEG were investigated. The strong Coulomb interaction between electrons and holes, which results in large binding energies of neutral excitons and negatively charged excitons (trions), allows one to address selectively the exciton or trion states by resonant optical excitation. Different scenarios of spin coherence generation were analyzed theoretically, among them the direct trion photocreation, the formation of trions from photogenerated excitons, and the electron-exciton exchange scattering. Good agreement between experiment and theory is found.

Magneto-gyrotropic photogalvanic effects in semiconductor quantum wells

We show that the sign of the circular photogalvanic effect can be changed by tuning the radiation frequency of circularly polarized light. Here resonant inversion of the photogalvanic effect has been observed for direct intersubband transition in n-type GaAs quantum well structures. This inversion of the photon helicity driven current is a direct consequence of the lifting of the spin degeneracy due to k-linear terms in the Hamiltonian in combination with energy and momentum conservation and optical selection rules.

Spin-dependent recombination in GaAsN solid solutions

Spin and valley-orbit splittings are calculated in symmetric

Interface optical anisotropy in a heterostructure with different cations and anions

\mathrm{Si}\mathrm{Ge}∕\mathrm{Si}∕\mathrm{Si}\mathrm{Ge}