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

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 two-dimensional 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 in-plane and out-of-plane components with space distribution scale comparable to the superlattice cell size which can be observed experimentally.Comment: 9 pages, 6 figure

Hall Conductance of a Two-Dimensional Electron Gas with Spin-Orbit Coupling at the Presence of Lateral Periodic Potential

We evaluate the distribution of Hall conductances in magnetic subbands of two-dimensional electron gas with Rashba spin-orbit (SO) coupling placed in a periodic potential and perpendicular magnetic field. In this semiconductor structure the spin-orbit coupling mixes the states of different magnetic subbands and changes the distribution of their Hall conductances in comparison with the case of spinless particles. The calculations were made for semiconductor structures with a weak ($AlGaAs/GaAs$) and relatively strong ($GaAs/InGaAs$) SO and Zeeman interactions. The Hall conductances of fully occupied magnetic subbands depend on the system parameters and can be changed when neighboring subbands touch each other. It was shown that in the real semiconductor structures with relatively strong SO coupling the distribution of Hall conductance differs from the quantization law predicted by Thouless et al\cite{Thoul} for systems without spin-orbit coupling. In the case of weak SO interaction and relatively large lattice period the Hall conductance of magnetic subbands are the same as for spinless particles, but as the lattice period decreases and two neighboring subbands touch each other the distribution of Hall conductances is changed drastically.Comment: 8 pages, 4 figure

Approximate Bayesian Image Interpretation using Generative Probabilistic Graphics Programs

The idea of computer vision as the Bayesian inverse problem to computer graphics has a long history and an appealing elegance, but it has proved difficult to directly implement. Instead, most vision tasks are approached via complex bottom-up processing pipelines. Here we show that it is possible to write short, simple probabilistic graphics programs that define flexible generative models and to automatically invert them to interpret real-world images. Generative probabilistic graphics programs consist of a stochastic scene generator, a renderer based on graphics software, a stochastic likelihood model linking the renderer's output and the data, and latent variables that adjust the fidelity of the renderer and the tolerance of the likelihood model. Representations and algorithms from computer graphics, originally designed to produce high-quality images, are instead used as the deterministic backbone for highly approximate and stochastic generative models. This formulation combines probabilistic programming, computer graphics, and approximate Bayesian computation, and depends only on general-purpose, automatic inference techniques. We describe two applications: reading sequences of degraded and adversarially obscured alphanumeric characters, and inferring 3D road models from vehicle-mounted camera images. Each of the probabilistic graphics programs we present relies on under 20 lines of probabilistic code, and supports accurate, approximately Bayesian inferences about ambiguous real-world images.Comment: The first two authors contributed equally to this wor

Evidence for field induced proximity type behavior in ferromagnetic nanofluid

We report some unusual magnetic properties observed in CoFe2O4 based ferrofluid (with an average particle size of D = 6 nm). More precisely, in addition to the low-field ferromagnetic (FM) phase transition with an intrinsic Curie temperature T_Cb=350K, a second phase transition with an extrinsic Curie temperature T_Cw = 266K emerges at higher (saturating) magnetic field. The transitions meet at the crossover point T_cr = 210 K. The origin of the second transition is attributed to magnetic field induced proximity type interaction between FM particles through non-FM layers

The long-term cyclotron dynamics of relativistic wave packets: spontaneous collapse and revival

In this work we study the effects of collapse and revival as well as {\it Zitterbewegung} (ZB) phenomenon, for the relativistic electron wave packets, which are a superposition of the states with quantum numbers sharply peaked around some level $n_0$ of the order of few tens. The probability densities as well as average velocities of the packet center and the average spin components were calculated analytically and visualized. Our computations demonstrate that due to dephasing of the states for times larger than the cyclotron period the initial wave packet (which includes the states with the positive energy only) loses the spatial localization so that the evolution can no longer be described classically. However, at the half-revival time $t=T_R/2$ its reshaping takes place firstly. The behavior of the wave packet containing the states of both energy bands (with $E_n>0$ and $E_n<0$) is more complicated. At short times of a few classical periods such packet splits into two parts which rotate with cyclotron frequency in the opposite directions and meet each other every one-half of the cyclotron period. At these moments their wave functions have significant overlap that leads to ZB. At the time of fractional revival each of two sub-packets is decomposed into few packets-fractions. However, at $t=T_R$ each of the two sub-packets (with positive or negative energy) restores at various points of the cyclotron orbit, that makes it impossible reshaping of initial wave packet entirely unlike the wave packet which consists of states with energies $E_n>0$ only. Obtained results can be useful for the description of electromagnetic radiation and absorption in relativistic plasma on astrophysics objects, where super high magnetic field has the value of the order $10^8-10^9$T, as well as for interpretation of experiments with trapped ions