Abstract-Terahertz photoresistivity of a high-mobility 3D topological insulator based on a strained HgTe film

M. L. Savchenko, M. Ottender, S. D. Ganichev, N. N. Mikhailov, Z. D. Kvon

https://arxiv.org/abs/2008.04695

We report on a detailed study of the terahertz (THz) photoresistivity in a strained HgTe three-dimensional topological insulator (3D TI) for all Fermi level positions: inside the conduction and valence bands, and in the bulk gap. In the presence of magnetic field we detected a resonance corresponding to the cyclotron resonance (CR) in top surface Dirac fermions (DF) and examined the nontrivial dependence of the surface state cyclotron mass on the Fermi level position. We also detected additional resonant features at moderate electron densities and demonstrated that they are caused by the interaction of surface DF and bulk electrons. At high electron densities, we observed THz radiation induced 1/B-periodic low-field magneto-oscillations coupled to harmonics of the CR and demonstrated that they have a common origin with microwave-induced resistance oscillations (MIRO) previously observed in high mobility GaAs based heterostructures.

Abstract-Sign-alternating photoconductivity and magnetoresistance oscillations induced by terahertz radiation in HgTe quantum wells

M. Otteneder, I. A. Dmitriev, S. Candussio, M. L. Savchenko, D. A. Kozlov, V. V. Bel'kov, Z. D. Kvon, N. N. Mikhailov, S. A. Dvoretsky, S. D. Ganichev

https://arxiv.org/abs/1807.10663

We report on the observation of terahertz radiation induced photoconductivity and of terahertz analog of the microwave-induced resistance oscillations (MIRO) in HgTe-based quantum well (QW) structures of different width. The MIRO-like effect has been detected in QWs of 20 nm thickness with inverted band structure and a rather low mobility of about 3 × 105 cm2/V s. In a number of other structures with QW widths ranging from 5 to 20 nm and lower mobility we observed an unconventional non-oscillatory photoconductivity signal which changes its sign upon magnetic field increase. This effect was observed in structures characterized by both normal and inverted band ordering, as well as in QWs with critical thickness and linear dispersion. In samples having Hall bar and Corbino geometries an increase of the magnetic field resulted in a single and double change of the sign of the photoresponse, respectively. We show that within the bolometric mechanism of the photoresponse these unusual features imply a non-monotonic behavior of the transport scattering rate, which should decrease (increase) with temperature for magnetic fields below (above) the certain value. This behavior is found to be consistent with the results of dark transport measurements of magnetoresistivity at different sample temperatures. Our experiments demonstrate that photoconductivity is a very sensitive probe of the temperature variations of the transport characteristics, even those that are hardly detectable using standard transport measurements

Abstract-Giant terahertz photoconductance of tunneling point contacts

M. Otteneder, Z. D. Kvon, O. A. Tkachenko, V. A. Tkachenko, A. S. Jaroshevich, E. E. Rodyakina, A. V. Latyshev, and S. D. Ganichev


https://journals.aps.org/prapplied/accepted/07074Ae7Z1f17b05b1811dd8e196af92cb8eaeaca

We report on the observation of the giant photoconductance of a quantum point contact (QPC) in tunneling regime excited by terahertz radiation. Studied QPCs are formed in a GaAs/AlGaAs heterostructure with a high-electron-mobility two-dimensional electron gas. We demonstrate that irradiation of strongly negatively biased QPCs by laser radiation with frequency $f=0.69$~THz and intensity 50~mW/cm${}^2$ results in two orders of magnitude enhancement of the QPC conductance. The effect increases with the dark conductivity decrease. It is also characterized by a strong polarization dependence and a drastic reduction of the signal by increasing the radiation frequency to 1.63 THz. We demonstrate that all experimental findings can be well explained by the photon-assisted tunneling through the QPC. Corresponding calculations are in good agreement with the experiment.

Abstract-Magnetoresistance oscillations induced by high-intensity terahertz radiation

T. Herrmann, Z. D. Kvon, I. A. Dmitriev, D. A. Kozlov, B. Jentzsch, M. Schneider, L. Schell, V. V. Bel’kov, A. Bayer, D. Schuh, D. Bougeard, T. Kuczmik, M. Oltscher, D. Weiss, and S. D. Ganichev

https://journals.aps.org/prb/accepted/7a079Oe8S5a1573025948ef2a7974268293e8629a

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/cm2 to 104 W/cm2 reveal high-power saturation of the MIRO amplitude, which is well described by an empirical fit function I/(1+I/I_s)^\beta with \beta~\sim 1. The saturation intensity I_s is of the order of tens of W/cm2and 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.

Abstract-Magneto-resistance oscillations induced by high-intensity terahertz radiation

T. Herrmann, Z. D. Kvon, I. A. Dmitriev, D. A. Kozlov, B. Jentzsch, M. Schneider, L. Schell, V. V. Bel'kov, A. Bayer, D. Schuh, D. Bougeard, T. Kuczmik, M. Oltscher, D. Weiss, S. D. Ganichev

(Submitted on 22 Jun 2017)

https://arxiv.org/abs/1706.07239

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/cm2 to 104 W/cm2 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/cm2 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.

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

K.-M. Dantscher, D. A. Kozlov, M. T. Scherr, S. Gebert, J. Bärenfänger, M. V. Durnev, S. A. Tarasenko, V. V. Bel'kov, N. N. Mikhailov, S. A. Dvoretsky, Z. D. Kvon, J. Ziegler, D. Weiss, and S. D. Ganichev

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.201103

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 $\approx 3\mu m$ 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.

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Quantum oscillations of photocurrents in HgTe quantum wells with Dirac and parabolic dispersions

C. Zoth1, P. Olbrich1, P. Vierling1, K.-M. Dantscher1, V. V. Bel'kov2, M. A. Semina2, M. M. Glazov2, L. E. Golub2, D. A. Kozlov3,4, Z. D. Kvon3,4, N. N. Mikhailov3, S. A. Dvoretsky3, and S. D. Ganichev1

• 1Terahertz Center, University of Regensburg, 93040 Regensburg, Germany
• 2Ioffe Physical-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg, Russia
• 3A.V. Rzhanov Institute of Semiconductor Physics, Novosibirsk 630090, Russia
• 4Novosibirsk State University, Novosibirsk 630090, Russia

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.205415

We report on the observation of magneto-oscillations of terahertz radiation induced photocurrent in HgTe/HgCdTe quantum wells of different widths, which are characterized by a Dirac-like, inverted, and normal parabolic band structure. The photocurrent data are accompanied by measurements of photoresistance (photoconductivity), radiation transmission, as well as magnetotransport. We develop a microscopic model of a cyclotron-resonance assisted photogalvanic effect, which describes main experimental findings. We demonstrate that the quantum oscillations of the photocurrent are caused by the crossing of Fermi level by Landau levels resulting in the oscillations of spin polarization and electron mobilities in spin subbands. Theory explains a photocurrent direction reversal with the variation of magnetic field observed in experiment. We describe the photoconductivity oscillations related with the thermal suppression of the Shubnikov–de Haas effect.

DOI: http://dx.doi.org/10.1103/PhysRevB.90.205415

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6 More

• Published 14 November 2014
• Received 4 July 2014
• Revised 29 August 2014

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