The paper reviews the interplay of Rashba/Dresselhaus spin splittings in various two‐dimensional systems made zinc‐blende III–V, wurtzite, and SiGe semiconductors. We discuss symmetry aspects linear cubic electron wavevector splitting heterostructures prepared on (001)‐, (110)‐, (111)‐, (113)‐, (112)‐, (013)‐ oriented substrates address requirements for suppression relaxation realization persistent helix state. In experimental part paper, we overview results probed by photogalvanic...

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 angular distribution spin-galvanic effect at certain directions spin orientation plane QW. ratio relevant coefficients can be deduced directly experiment does not relay theoretically obtained quantities. Thus our...

Spin relaxation in-plane anisotropy is predicted for heterostructures based on zinc-blende semiconductors. It shown that it manifests itself especially brightly if the two spin mechanisms (D'yakonov-Perel' and Rashba) are comparable in efficiency. demonstrated quantum well grown along [0 0 1] direction, main axes of rate tensor [1 1 0] -1 0].

The spin-galvanic effect and the circular photogalvanic induced by terahertz radiation are applied to determine relative strengths of Rashba Dresselhaus band spin splitting in (001)-grown GaAs InAs based two dimensional electron systems. We observed that shifting $\ensuremath{\delta}$-doping plane from one side quantum well other results a change sign photocurrent caused while term remains. measurements give necessary feedback for technologists looking structures with equal splittings or...

In layered semiconductors with spin-orbit interaction (SOI) a persistent spin helix (PSH) state suppressed relaxation is expected if the strengths of Rashba and Dresselhaus SOI terms, $\ensuremath{\alpha}$ $\ensuremath{\beta}$, are equal. Here we demonstrate gate control detection PSH in two-dimensional electron systems strong including terms cubic momentum. We consider strain-free InGaAs/InAlAs quantum wells first determine ratio $\ensuremath{\alpha}/\ensuremath{\beta}\ensuremath{\simeq}1$...

We report on the observation of photogalvanic effects in epitaxially grown Sb2Te3 and Bi2Te3 three-dimensional (3D) topological insulators (TI). show that asymmetric scattering Dirac fermions driven back forth by terahertz electric field results a dc current. Because "symmetry filtration" current is generated surface electrons only provides an optoelectronic access to probe electron transport TI, domains orientation, details 3D TI even at room temperature.

Experimental and theoretical studies on ratchet effects in graphene with a lateral superlattice excited by alternating electric fields of terahertz frequency range are presented. A superlatice deposited top monolayer is formed either periodically repeated metal stripes having different widths spacings or inter-digitated comb-like dual-grating-gate (DGG) structures. We show that the photocurrent radiation sensitive to polarization state can be efficiently controlled back gate driving system...

Abstract Second-harmonic generation (SHG) is a non-linear optical process, where two photons coherently combine into one photon of twice their energy. Efficient SHG occurs for crystals with broken inversion symmetry, such as transition metal dichalcogenide monolayers. Here we show tuning processes in an symmetric crystal. This tunability based on the unique properties bilayer MoS 2 , that shows strong oscillator strength intra- but also interlayer exciton resonances. As tune signal onto...

Spin relaxation is investigated theoretically in two-dimensional systems. Various semiconductor structures of both n and p types are studied detail. The most important spin mechanisms considered. times calculated taking into account the contributions to spin-orbit interaction due bulk inversion asymmetry structure asymmetry. It shown that in-plane anisotropy electron appears III-V asymmetrical heterostructures. This may be controlled by external parameters, differ several orders magnitude.

We report experimental and theoretical investigations of the quantized hole states in a magnetic field. observe spin quantum beats time-resolved photoluminescence N-modulation-doped ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ wells field perpendicular to growth direction. The measurement these beats, which originate from Larmor precession heavy-hole spins, yields accurate determination transverse Land\'e g factor. find...

We show that the optical excitation of graphene with polarized light leads to pure valley current for which carriers in valleys counterflow. The each originates from asymmetry transitions and electron scattering by impurities owing warping energy spectrum. has strong polarization dependence; its direction is opposite normally incident beams orthogonal linear polarizations. In undoped on a substrate high susceptibility, electron-electron an additional contribution can dominate.

We report on the observation of a terahertz radiation induced photon drag effect in epitaxially grown $n$- and $p$-type (Bi$_{1-x}$Sb$_{x}$)$_{2}$Te$_{3}$ three dimensional topological insulators with different antimony concentrations $x$ varying from 0 to 1. demonstrate that excitation polarized results $dc$ electric photocurrent. While at normal incidence current arises due photogalvanic surface states, oblique it is outweighed by trigonal effect. The developed microscopic model theory...

Emission from excited excitons in monolayers of transition metal dichalcogenides, which are ultrathin semiconductors, is more efficient than conventional The studied interactions between important for devices such as lasers and optical amplifiers.

Optical properties of transition metal dichalcogenides monolayers are controlled by Wannier-Mott excitons forming a series $1s,2s,2p,...$ hydrogen-like states. We develop the theory excited excitonic states energy spectrum fine structure. predict that $p$- and $s$-shell mixed due to specific ${D}_{3h}$ point symmetry dichalcogenide monolayers. Hence, both $s$- $p$-shell active in single- two-photon processes, providing an efficient mechanism second harmonic generation. The corresponding...

Spin-relaxation times of two-dimensional electrons in asymmetrical (001) AlGaAs quantum wells are measured by means Hanle effect. Three different spin-relaxation for spins oriented along [110], $[1\overline{1}0]$, and [001] crystallographic directions extracted demonstrating anisotropy the D'yakonov-Perel' spin relaxation mechanism. The relative strengths Rashba Dresselhaus terms describing spin-orbit coupling semiconductor well structures obtained. It is shown that splitting about four...

Spin splitting of conduction electron states has been analyzed for all possible point symmetries SiGe quantum well structures. A particular attention is paid to removal spin degeneracy caused by the rotoinversion asymmetry a (001) heterointerface between two diamond-lattice materials. The shown result in both Rashba and Dresselhaus types symmetrical wells. Consequences on relaxation are discussed.

Spin and valley-orbit splittings are calculated in symmetric $\mathrm{Si}\mathrm{Ge}∕\mathrm{Si}∕\mathrm{Si}\mathrm{Ge}$ quantum wells (QWs) by using the tight-binding approach. In accordance with symmetry considerations an existence of spin splitting electronic states perfect QWs odd number Si atomic planes is microscopically demonstrated. The oscillates QW width these oscillations related to intervalley reflection electron wave from interfaces. It shown that under study can efficiently be...

The circular photon drag effect is observed in a bulk semiconductor. photocurrent caused by transfer of both translational and angular momenta light to charge carriers detected tellurium the midinfrared frequency range. Dependencies on polarization incidence angle agree with symmetry analysis effect. Microscopic models are developed for intra- intersubband optical absorption valence band tellurium. shift contribution current calculated. An decrease increase energy explained theory...

This paper suggests that an optical method can be used to reliably probe valley polarization in graphene. It shows at normal incidence of photons, imbalance carrier populations two valleys gives rise second harmonic generation graphene which experimentally determine both the degree and sign polarization.

We develop a theory of the direct interband and indirect intraband photogalvanic effects in Weyl semimetals belonging to gyrotropic classes with improper symmetry operations. At zero magnetic field, an excitation such material circularly polarized light leads photocurrent whose direction depends on helicity. show that C$_{2v}$ symmetry, allowance for tilt term effective Hamiltonian is enough prevent cancellation contributions from cones opposite chiralities. In case C$_{4v}$ addition it...

We report on the observation of ratchet effect -- generation direct electric current in response to external terahertz (THz) radiation bilayer graphene, where inversion symmetry is broken by an asymmetric dual-grating gate potential. As a central result, we demonstrate that at high temperature, $T = 150~\textrm{K}$, decreases frequencies as $ \propto 1/\omega^2$, while low 4.2~\textrm{K}$, frequency dependence becomes much stronger $\propto 1/\omega^6$. The developed theory shows very...

The theory of the linear photogalvanic effect is developed for direct optical transitions between surface states three-dimensional topological insulators. photocurrent governed by orientation polarization plane light and caused warping energy dispersion two-dimensional carriers calculated. It shown that both shift contribution coordinate shifts particle wave packets during ballistic interference absorption scattering disorder have generally same order magnitude. present owing to...

A theory of weak antilocalization is developed for high-mobility two-dimensional systems. Spin-orbit interaction Rashba and Dresselhaus types taken into account. Anomalous magnetoresistance calculated in the whole range classically magnetic fields arbitrary strength spin-orbit splitting. The obtained expressions are valid both ballistic diffusive regimes localization. proposed includes backscattering nonbackscattering contributions to conductivity. It shown that field dependence conductivity...

The circular photogalvanic effect, induced by infrared radiation, has been observed in (0001)-oriented n-GaN low dimensional structures. photocurrent changes sign upon reversing the radiation helicity demonstrating existence of spin splitting conduction band k space this type materials. observation suggests presence a sizeable Rashba splitting, caused built-in asymmetry at AlGaN∕GaN interface.