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

P. Faltermeier, G. V. Budkin, J. Unverzagt, S. Hubmann, A. Pfaller, V. V. Bel'kov, L. E. Golub, E. L. Ivchenko, Z. Adamus, G. Karczewski, T. Wojtowicz, V. V. Popov, D. V. Fateev, D. A. Kozlov, D. Weiss, S. D. Ganichev

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.155442

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.

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Abstract-Terahertz ratchet effects in graphene with a lateral superlattice

P. Olbrich, J. Kamann, M. König, J. Munzert, L. Tutsch, J. Eroms, D. Weiss, Ming-Hao Liu (劉明豪), L. E. Golub, E. L. Ivchenko, V. V. Popov, D. V. Fateev, K. V. Mashinsky, F. Fromm, Th. Seyller, and S. D. Ganichev

Phys. Rev. B 93, 075422 – Published 12 February 2016

http://journals.aps.org/prb/abstract/10.1103/PhysRevB.93.075422

Experimental and theoretical studies on ratchet effects in graphene with a lateral superlattice excited by alternating electric fields of terahertz frequency range are presented. A lateral superlattice deposited on top of monolayer graphene is formed either by periodically repeated metal stripes having different widths and spacings or by interdigitated comblike dual-grating-gate (DGG) structures. We show that the ratchet photocurrent excited by terahertz radiation and sensitive to the radiation polarization state can be efficiently controlled by the back gate driving the system through the Dirac point as well as by the lateral asymmetry varied by applying unequal voltages to the DGG subgratings. The ratchet photocurrent includes the Seebeck thermoratchet effect as well as the effects of “linear” and “circular” ratchets, sensitive to the corresponding polarization of the driving electromagnetic force. The experimental data are analyzed for the electronic and plasmonic ratchets taking into account the calculated potential profile and the near field acting on carriers in graphene. We show that the photocurrent generation is based on a combined action of a spatially periodic in-plane potential and the spatially modulated light due to the near-field effects of the light diffraction.

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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

©2014 American Physical Society