We report on the observation of photogalvanic effects in epitaxially grown Sb2Te3 and Bi2Te3 three-dimensional (3D) topological insulators (TI). We show that asymmetric scattering of Dirac fermions driven back and forth by the terahertz electric field results in a dc electric current. Because of the "symmetry filtration" the dc current is generated by the surface electrons only and provides an optoelectronic access to probe the electron transport in TI, surface domains orientation, and details of electron scattering in 3D TI even at room temperature.
We report on the observation of a terahertz radiation-induced photon drag effect in epitaxially grown nand p-type (Bi 1−x Sb x ) 2 Te 3 three-dimensional topological insulators with different antimony concentrations x varying from 0 to 1. We demonstrate that the excitation with polarized terahertz radiation results in a dc electric photocurrent. While at normal incidence a current arises due to the photogalvanic effect in the surface states, at oblique incidence it is outweighed by the trigonal photon drag effect. The developed microscopic model and theory show that the photon drag photocurrent can be generated in surface states. It arises due to the dynamical momentum alignment by time-and space-dependent radiation electric field and implies the radiation-induced asymmetric scattering in the electron momentum space. We show that the photon drag current may also be generated in the bulk. Both surface states and bulk photon drag currents behave identically upon variation of such macroscopic parameters as radiation polarization and photocurrent direction with respect to the radiation propagation. This fact complicates the assignment of the trigonal photon drag effect to a specific electronic system.
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. DOI: 10.1103/PhysRevB.94.081301 One of the most interesting phenomena recently observed in two-dimensional electron systems (2DES) is microwave (MW) -induced resistance oscillations (MIRO) and associated zero resistance states (ZRS) [1][2][3][4][5][6][7], reviewed, e.g., in [8]. Like Shubnikov-de Haas oscillations (SdH), MIRO are periodic on a 1/B scale, but occur at lower magnetic fields and show much weaker temperature dependence. Phenomenologically, they are very similar to Weiss oscillations [9], which reflect the commensurability between the cyclotron orbit radius and the period of a periodic potential. MIRO by contrast, reflect the commensurability between the MW photon energy 2π f and the cyclotron energy ω c . In extremely clean samples the minima of the MIRO develop into ZRS [3][4][5], which are explained [10] in terms of an instability of the system and formation of current domains, occurring when the conductivity becomes negative under MW irradiation (see also [8,11,12]).In spite of numerous experiments and significant advances in their theoretical understanding, there is still no commonly accepted microscopic description of the effect [13,14] and the ongoing MIRO investigations remain challenging [15][16][17][18][19][20][21]. Consequently, new materials have been studied [22][23][24][25] and new theoretical models have been put forward [26][27][28][29][30]. To the most pressing issues which need to be clarified experimentally and which might help to differentiate between the different models belong the MIRO polarization dependence [7,8,31] and the "bulk" or "edge" nature of the effect.So far the majority of experimental work has been done in the MW regime (1-350 GHz) and there are only a few reports on MIRO excited at terahertz (THz) frequencies [32][33][34]. Here we report on the observation of pronounced MIRO-like oscillations induced by THz radiation. We exploit the specific advantages of THz laser radiation not present in the MW regime, i.e., the possibility to focus it onto a spot smaller than the sample's size and easy control of the radiation's polarization. The most important features clearly detected on a large variety of samples are (i) a very weak dependence of the oscillations' amplitude on the photon helicity and (ii) the bulk nature of the effect. Furthermore, our study shows that the MIRO oscillations can be excited at THz frequencies even in the samples with low mobility, whereas in the MW range ultrahigh mobility samples are crucially needed for this type of experimen...
We report on observation of pronounced terahertz radiation-induced magneto-resistivity oscillations in AlGaAs/GaAs two-dimensional electron systems, the THz analog of the microwave induced resistivity oscillations (MIRO). Applying high power radiation of a pulsed molecular laser we demonstrate that MIRO, so far observed at low power only, are not destroyed even at very high intensities. Experiments with radiation intensity ranging over five orders of magnitude from 0.1 W/cm 2 to 10 4 W/cm 2 reveal high-power saturation of the MIRO amplitude, which is well described by an empirical fit function I/(1 + I/Is) β with β ∼ 1. The saturation intensity Is is of the order of tens of W/cm 2 and increases by six times by increasing the radiation frequency from 0.6 to 1.1 THz. The results are discussed in terms of microscopic mechanisms of MIRO and compared to nonlinear effects observed earlier at significantly lower excitation frequencies.Magnetotransport experiments in low-dimensional systems containing high mobility two-dimensional electron gases (2DEG) reveal many fundamental phenomena of quite different physical nature. The most prominent and well-known examples in linear dc transport are integer and fractional quantum Hall effects 1,2 in stronger magnetic field and Shubnikov -de Haas (SdH) 3,4 and Weiss 5oscillations at moderate fields. While linear transport phenomena in low-dimensional semiconductor systems have been systematically studied for several decades, in the last years terahertz/microwave-induced nonequilibrium transport in 2DEG is attracting an ever growing attention. In part, this is caused by the steadily expanding frequency range and rapid developments of terahertz science and technology [6][7][8][9][10][11] . Following the discovery of the microwave-induced resistance oscillations (MIRO) 12,13 and associated zero-resistance states 14-18 , the focus of recent research has largely shifted to nonequilibrium magnetotransport phenomena 19 . Similar to the SdH and Weiss oscillations, MIRO are 1/B-periodic oscillations and reflect the commensurability between the photon energy 2π f and the cyclotron energy ω c . Here, is the reduced Planck constant, f the microwave frequency and ω c the cyclotron frequency. Very recently, it was demonstrated that MIRO can be efficiently excited at substantially higher frequencies of several terahertz 20 . This work gave an experimental answer to two currently most intriguing questions regarding radiation helicity 18 and the role of the contacts/edges 21,22 . So far all studies of MIRO were performed at low radiation power smaller or of the order of a milliwatt19 . Here we demonstrate that MIRO are very robust and do not vanish even at very high power up to tens of kW/cm 2 . We have studied MIRO for frequencies between 0.6 and 1.1 THz and intensities varying by five orders of magnitude. We observe that high radiation intensity affects exclusively the amplitude of MIRO while both shape and phase of the oscillations are preserved. For all frequencies and all oscillation orde...
We report on the study of terahertz radiation induced MIRO-like oscillations of magneto-resistivity in GaAs heterostructures. Our experiments provide an answer on two most intriguing questionseffect of radiation helicity and the role of the edges -yielding crucial information for understanding of the MIRO origin. Moreover, we demonstrate that the range of materials exhibiting radiationinduced magneto-oscillations can be largely extended by using high-frequency radiation. ǫ /A CRI ǫ can only increase, see Suppl. Material.
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