Analog of microwave-induced resistance oscillations induced in GaAs heterostructures by terahertz radiation

We report on the study of terahertz radiation-induced MIRO-like oscillations of magnetoresistivity in GaAs heterostructures. Our experiments provide an answer on two most intriguing questions-effect of radiation helicity and the role of the edges-yielding crucial information for an understanding of the MIRO (microwave-induced resistance oscillations) origin. Moreover, we demonstrate that the range of materials exhibiting radiation-induced magneto-oscillations can be largely extended by using high-frequency radiation

Magnetic quantum ratchet effect in (Cd,Mn)Te- and CdTe-based quantum well structures with a lateral asymmetric superlattice

We report on the observation of magnetic quantum ratchet effect in (Cd, Mn) Te-and CdTe-based quantum well structures with an asymmetric lateral dual grating gate superlattice subjected to an external magnetic field applied normal to the quantum well plane. A dc electric current excited by cw terahertz laser radiation shows 1/B oscillations with an amplitude much larger as compared to the photocurrent at zero magnetic field. We show that the photocurrent is caused by the combined action of a spatially periodic in-plane potential and the spatially modulated radiation due to the near-field effects of light diffraction. Magnitude and direction of the photocurrent are determined by the degree of the lateral asymmetry controlled by the variation of voltages applied to the individual gates. The observed magneto-oscillations with enhanced photocurrent amplitude result from Landau quantization and, for (Cd, Mn) Te at low temperatures, from the exchange enhanced Zeeman splitting in diluted magnetic heterostructures. Theoretical analysis, considering the magnetic quantum ratchet effect in the framework of semiclassical approach, describes quite well the experimental results

Photogalvanic probing of helical edge channels in two-dimensional HgTe topological insulators

We report on the observation of a circular photogalvanic current excited by terahertz laser radiation in helical edge channels of two-dimensional (2D) HgTe topological insulators (TIs). The direction of the photocurrent reverses by switching the radiation polarization from a right-handed to a left-handed one and, for fixed photon helicity, is opposite for the opposite edges. The photocurrent is detected in a wide range of gate voltages. With decreasing the Fermi level below the conduction band bottom, the current emerges, reaches a maximum, decreases, changes its sign close to the charge neutrality point (CNP), and again rises. Conductance measured over a approximate to 3 mu m distance at CNP approaches 2e(2)/ h, the value characteristic for ballistic transport in 2D TIs. The data reveal that the photocurrent is caused by photoionization of helical edge electrons to the conduction band. We discuss the microscopic model of this phenomenon and compare calculations with experimental data

Spin-orbit coupling in gyrotropic quantum wells by far-infrared radiation induced spin-galvanic effect

The Rashba effect, whose experimental access is usually masked by the Dresselhaus effect, allows manipulation of spins in semiconductor spintronics. Based on the far-infrared radiation induced spin-galvanic effect, we present a unique way to separate both types of spin-orbit coupling

Spin-galvanic effect

There is much recent interest in exploiting the spin of conduction electrons in semiconductor heterostructures together with their charge to realize new device concepts1. Electrical currents are usually generated by electric or magnetic fields, or by gradients of, for example, carrier concentration or temperature. The electron spin in a spin-polarized electron gas can, in principle, also drive an electrical current, even at room temperature, if some general symmetry requirements are met. Here we demonstrate such a ‘spin-galvanic’ effect in semiconductor heterostructures, induced by a non-equilibrium, but uniform population of electron spins. The microscopic origin for this effect is that the two electronic sub-bands for spin-up and spin-down electrons are shifted in momentum space and, although the electron distribution in each sub-band is symmetric, there is an inherent asymmetry in the spin-flip scattering events between the two sub-bands. The resulting current flow has been detected by applying a magnetic field to rotate an optically oriented nonequilibrium spin polarization in the direction of the sample plane. In contrast to previous experiments, where spin-polarized currents were driven by electric fields in semiconductor2,3, we have here the complementary situation where electron spins drive a current without the need of an external electric field

Magneto-Gyrotropic Photogalvanic Effect in Semiconductor Quantum Wells

A new type of infrared induced photocurrents is reported occurring in gyrotropic quantum wells in the presence of a magnetic field. The effect is caused by spin-orbit interaction and may be observed even for unpolarized radiation. The current occurs for particular relative orientation between magnetic field, current and crystallographic orientation