In layered semiconductors with spin-orbit interaction (SOI) a persistent spin helix (PSH) state with suppressed spin relaxation is expected if the strengths of the Rashba and Dresselhaus SOI terms, α and β, are equal. Here we demonstrate gate control and detection of the PSH in two-dimensional electron systems with strong SOI including terms cubic in momentum. We consider strain-free InGaAs/InAlAs quantum wells and first determine a ratio α/β 1 for nongated structures by measuring the spin-galvanic and circular photogalvanic effects. Upon gate tuning the Rashba SOI strength in a complementary magnetotransport experiment, we monitor the complete crossover from weak antilocalization via weak localization to weak antilocalization, where the emergence of weak localization reflects a PSH-type state. A corresponding numerical analysis reveals that such a PSH-type state indeed prevails even in presence of strong cubic SOI, however no longer at α = β. An electron moving in an electric field experiences, in its rest frame, an effective magnetic field pointing perpendicularly to its momentum. The coupling of the electron's spin to this magnetic field is known as spin-orbit interaction (SOI). The ability to control the corresponding magnetic field, and thereby spin states, all electrically in gated semiconductor heterostructures 1,2 is a major prerequisite and motivation for research towards future semiconductor spintronics. However, on the downside, the momentum changes of an electron moving through a semiconductor cause sudden changes in the magnetic field leading to spin randomization. Hence, suppression of spin relaxation in the presence of strong, tunable SOI is a major challenge of semiconductor spintronics.In III-V semiconductor heterostructures two different types of SOI exist: (i) Rashba SOI, 3 originating from structure inversion asymmetry (SIA), is linear in momentum k with a strength α that can be controlled by an electric gate.(ii) Dresselhaus SOI 4 is due to bulk inversion asymmetry (BIA), which gives rise to a band spin splitting, given by k-linear and k-cubic contributions. 5 The strength of the linear in k term β = γ k 2 z (where γ is a material parameter) can hardly be changed as it stems from crystal fields. These various spin-orbit terms in layered semiconductors are described by the Hamiltonian H SO = H R + H D with Rashba and Dresselhaus termswith σ x ,σ y the Pauli spin matrices. 7 If the k-cubic terms can be neglected, a special situation emerges if Rashba and Dresselhaus SOI are of equal strength: α = ±β.Then spin relaxation is suppressed. 8,9 A collinear alignment of Rashba and Dresselhaus effective magnetic fields gives rise to spin precession around a fixed axis, leading to spatially periodic modes referred to as persistent spin helix (PSH) and reflecting the underlying SU (2) symmetry in this case. 10The PSH is robust against all forms of spin-independent scattering. This favorable situation where spin relaxation is suppressed while the spin degree of freedom is still susceptible to electric...

We measured the Dresselhaus spin-orbit interaction coefficient β 1 for (001)-grown GaAs/Al 0.3 Ga 0.7 As quantum wells for six different well widths w between 6 and 30 nm. The varying size quantization of the electron wave vector z-component k 2 z ∼ (π/w) 2 influences β 1 = −γ k 2 z linearly. The value of the bulk Dresselhaus coefficient γ = (−11 ± 2) eVÅ 3 was determined. We discuss the absolute sign of the Landé g factors and the effective momentum scattering times.

Both structure and bulk inversion asymmetry in modulation-doped ͑001͒-grown GaAs quantum wells were investigated employing the magnetic field induced photogalvanic effect. We demonstrate that the structure inversion asymmetry ͑SIA͒ can be accurately tailored by the delta-doping layer position. Symmetrically doped structures exhibit a substantial SIA due to impurity segregation during the growth process. Tuning the SIA by the delta-doping position, we can grow samples with almost equal degrees of structure and bulk inversion asymmetry.

We report on the study of the linear and circular magnetogyrotropic photogalvanic effect (MPGE) in GaAs/AlGaAs quantum well structures. Using the fact that in such structures the Landé factor g * depends on the quantum well (QW) width and has different signs for narrow and wide QWs, we succeeded to separate spin and orbital contributions to both MPGEs. Our experiments show that, for most QW widths, the MPGEs are mainly driven by spin-related mechanisms, which results in a photocurrent proportional to the g * factor. In structures with a vanishingly small g * factor, however, linear and circular MPGE are also detected, proving the existence of orbital mechanisms.

We report on microwave (mw) radiation induced electric currents in (Cd,Mn)Te/(Cd,Mg)Te and InAs/(In,Ga)As quantum wells subjected to an external in-plane magnetic field. The current generation is attributed to the spin-dependent energy relaxation of electrons heated by mw radiation. The relaxation produces equal and oppositely directed electron flows in the spin-up and spin-down subbands yielding a pure spin current. The Zeeman splitting of the subbands in the magnetic field leads to the conversion of the spin flow into a spin-polarized electric current.

In layered semiconductors with spin-orbit interaction (SOI) a persistent spin helix (PSH) state with suppressed spin relaxation is expected if the strengths of the Rashba and Dresselhaus SOI terms, α and β, are equal. Here we demonstrate gate control and detection of the PSH in two-dimensional electron systems with strong SOI including terms cubic in momentum. We consider strain-free InGaAs/InAlAs quantum wells and first determine a ratio α/β ≃ 1 for non-gated structures by measuring the spin-galvanic and circular photogalvanic effects. Upon gate tuning the Rashba SOI strength in a complementary magneto-transport experiment, we then monitor the complete crossover from weak antilocalization via weak localization to weak antilocalization, where the emergence of weak localization reflects a PSH type state. A corresponding numerical analysis reveals that such a PSH type state indeed prevails even in presence of strong cubic SOI, however no longer at α = β.

We report on microwave (mw) radiation induced electric currents in (Cd,Mn)Te/(Cd,Mg)Te and InAs/(In,Ga)As quantum wells subjected to an external in-plane magnetic field. The current generation is attributed to the spin-dependent energy relaxation of electrons heated by mw radiation. The relaxation produces equal and oppositely directed electron flows in the spin-up and spin-down subbands yielding a pure spin current. The Zeeman splitting of the subbands in the magnetic field leads to the conversion of the spin flow into a spin-polarized electric current.PACS numbers: 73.21. Fg, 72.25.Fe, 78.67.De, 73.63.Hs The discovery of microwave induced oscillations in the resistivity of a two-dimensional electron gas (2DEG) attracted growing attention to an electron magnetotransport in semiconductor nanostructures subjected to mw radiation, see, e.g., [1,2]. The experimental observation of mw-induced effects stimulated much theoretical interest (see [3] and references therein) since they provide information which is complementary to conventional transport. In addition, the mw-induced effects offer new ways for developing sensitive microwave detectors [4]. All these effects have been observed applying an external magnetic field perpendicularly to a 2DEG plane.In this Letter we demonstrate that microwave radiation induces a novel electron transport effect also under an in-plane magnetic field, i.e., in the geometry that excludes the cyclotron motion and Landau quantization of the two-dimensional electrons. The effect is caused by an asymmetric spin-dependent electron energy relaxation of the 2DEG heated by mw radiation [5,6]. In an external magnetic field, this process results in a spin-polarized electric current. The mw-induced currents are observed in two different semiconductor systems: diluted magnetic semiconductor (DMS) (Cd,Mn)Te/(Cd,Mg)Te quantum wells (QWs) and InAs/(In,Ga)As QWs. In these structures the spin-polarized electric currents are enhanced due to either the presence of magnetic Mn 2+ ions [6] or the strong spin-orbit coupling in InAs [5].Two n-type doped QW structures have been grown by molecular-beam epitaxy on (001)-oriented substrates. The first sample has a digital alloy DMS QW [7], which is a 10 nm-wide CdTe QW containing three monolayers of Cd 0.86 Mn 0.14 Te (see inset in . Insets show the experimental geometry and the structure sketch.

The concept of spin-based electronics demands heterostructures possessing high electron mobility, pronounced ferromagnetic properties, and strong spin-orbit interaction (SOI).1,2 In particular, manganese doped diluted magnetic semiconductors (DMS) showing high Curie temperature and large Landé factor are in the focus of current research. While enhanced magnetic properties have been obtained in (Cd,Mn)Te-and (Ga,Mn)As-based quantum wells (QWs), the SOI in these materials is rather small. Thus, realization of DMS heterostructures based on materials which possess a strong SOI, e.g., InAs, becomes important. Most recently, it has been demonstrated that the incorporation of Mn into a heterostructure device containing an InAlAs/InGaAs QW leads to a two-dimensional hole gas.3 In these structures, the Mn ions are in close proximity to the InGaAs channel hosting the hole gas. While DMS hole systems with strong SOI have been realized and demonstrate very interesting magnetotransport properties, 4 the fabrication of InAs-based DMS with high mobility two-dimensional electron gas (2DEG) channels is still a challenge. The 2DEG is characterized by a simple parabolic band structure and much higher mobility compared to that of the holes, even in Mn-doped DMS structures like (Cd,Mn)Te QW (Ref. 5) features making 2DEG systems attractive for various applications. The only In(Mn)As-based superlattice with electron mobility l from 10 2 to 10 3 cm 2 /Vs has been realized in Ref. 6. Here, we report on the fabrication of Mn modulation doped structures with an InAs 2DEG channel. The QWs were grown applying III-V/II-VI "hybrid" technique following the recipes given in Ref. 7. The Mn layers have been inserted into the II-VI barrier. To explore the magnetic properties of the 2DEG, we investigated spin polarized electric currents induced by microwave (mw) radiation. 8,9 Our measurements show that hybrid AlSb/InAs/(Zn,Mn)Te QWs are characterized by enhanced magnetic properties which can be changed by tuning of the spatial position of Mn-doping layer as well as by the variation of temperature.The structures were grown on (001)-oriented GaAs semiinsulating substrates at temperature of 280 C. For the fabrication of AlSb/InAs/(Zn,Mn)Te heterovalent structures with Mn-containing barriers, we used two separated MBE setups. The first, Riber 32P, was employed to obtain the III-V part consisting of the 0.2 lm-thick GaAs and 2 lm-thick GaSb buffer layers capped with a 4 nm-thick AlSb barrier and a 15 nm-thick InAs QW (two last layers have common InSb-like interface). A (2.5 nm-GaSb/2.5 nm-AlSb) 10 superlattice was placed within the first third of the GaSb buffer to suppress propagation of misfit-induced threading dislocations. The II-VI parts of the structures were deposited pseudomorphically on the III-V part in the second two-chambers MBE setup (Semiteq) after the ex-situ sulfur chemical passivation in a 1M Na 2 S 9H 2 O solution of the top InAs layer. The coherent growth of ZnTe on InAs was initiated by simultaneous opening of Zn and Te fluxes onto ...