Terahertz radiation-induced conductivity, Kerr and Faraday angles, and spin textures in a two-dimensional electron gas with spin-orbit coupling subjected to a high magnetic field and periodic potential

Abstract

The terahertz radiation-induced conductivity and dielectric polarization tensors as well as the Faraday and Kerr rotation angles and the non-equilibrium spin textures are studied for twodimensional electron gas with strong spin-orbit coupling subjected to high magnetic field and to tunable periodic potential of a two-dimensional gated superlattice. It is found that both real and imaginary parts of the frequency-dependent induced conductivity approach maximum values with sharp and detectable peaks at frequencies corresponding to the inter-subband transitions between spin-split magnetic subbands. The observed properties of the conductivity tensor frequency dependence are applied for the description of the Kerr and Faraday rotation angles which can be used as another experimental tool for describing the electron gas in periodic structures with significant spin-orbit coupling. The formation of radiation-induced spin textures is predicted having both inplane and out-of-plane components with space distribution scale comparable to the superlattice cell size which can be observed experimentally.

Energy spectrum, the spin polarization, and the optical selection rules of the Kronig-Penney superlattice model with spin-orbit coupling

“…An electron in a fully occupied valence band can absorb a photon and then be excited to the high-energy conduction band; the formation of the exciton state in a semiconductor is an illustration. To understand the optical properties [25] of the spin-orbital superlattice system, it is instructive to know the electric-dipole transition rate between different bands [40],…”

Quantum states and linear response in dc and electromagnetic fields for the charge current and spin polarization of electrons at the Bi/Si interface with the giant spin-orbit coupling

“…The photon energy interval is chosen to cover the whole energy band range of the four lowest bands shown in Fig.2 where the most effective transitions occur between the states below and above the Fermi level. One can see that both the in-plane spin components S x , S y and the out-of plane component S z can be excited on a comparable scale which is a distinguishable feature of the lower hexagonal symmetry combined with Rashba SO coupling compared with one-dimensional 26,34,36 or twodimensional square 35 lattices with Rashba SO coupling. If one compares the results for x-and y-polarized radiation in Fig.6 and Fig.7, it can be seen that, similar to the dc current properties discussed in the previous Sec., the x ↔ y lattice and energy band asymmetry in the hexagonal geometry of the whole problem is reflected here in different shape and amplitude for the absorption coefficients in Fig.6(a) and 7(a).…”

“…[24][25][26][27] Besides the response to the dc electric field, the optical properties of SO-split band spectrum always attracted significant attention starting from the conventional semiconductor structures with big SO coupling. [28][29][30][31][32] In our previous papers we have observed an important role of SO coupling in conventional InGaAs-based semiconductor superlattices on the energy band formation 33 which directly affected both charge and spin response for the excitation by the electromagnetic radiation 34,35 and by the dc electric field. 36 It is known that the spin polarization configurations in semiconduc-tors may have a rather long relaxation time 4,37,38 which makes them as important as the conventional charge current setups for their applications in the nanoelectronics and spintronics.…”

“…(9). The examples of such systems with zero total spin polarization but non-zero spin spatial distribution (spin textures) can be found among the models of semiconductor superlattices with SO coupling both with 35 and without 34,36 external magnetic field, but their experimental observation and device application are currently limited by the probe and manipulation technology of the size of artificial superlattices and quantum wells rather then probing and utilizing the spatial magnetic configurations on the scale of individual atoms in the lattice. As to the predicted non-zero mean values of the induced spin such as those predicted here for Bi/Si, they are related to the whole sample and thus should be detectable.…”

“…The second quantity which frequency dependence we shall present together with the absorption is the induced spin polarization S m (ω) which can be derived by applying the Kubo linear response theory 35,41,42 and has the following form:…”