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-Suppressed Auger scattering and tunable light emission of Landau-quantized massless Kane electrons

D. B. But, M. Mittendorff, C. Consejo, F. Teppe, N. N. Mikhailov, S. A. Dvoretskii, C. Faugeras, S. Winnerl, M. Helm, W. Knap, M. Potemski & M. Orlita

https://www.nature.com/articles/s41566-019-0496-1

The Landau level laser was proposed long ago as a unique source of monochromatic radiation that would be widely tunable in the THz and infrared spectral ranges using a magnetic field. However, despite many efforts, this appealing concept never progressed to the design of a reliable device. This is because of the efficient Auger scattering of Landau-quantized electrons, an intrinsic non-radiative recombination channel that eventually gains over cyclotron emission in all materials studied so far (conventional semiconductors with parabolic bands, but also in graphene with massless electrons). Auger processes are favoured in these systems because the Landau levels (or their subsets) are equally spaced in energy. Here, we show that this scheme does not apply to massless Kane electrons in gapless HgCdTe, where undesirable Auger scattering is strongly suppressed and sizeable cyclotron emission is observed. The gapless HgCdTe thus appears as a material of choice for future Landau level lasers.

Abstract-Features of Photoluminescence of Double Acceptors in HgTe/CdHgTe Heterostructures with Quantum Wells in a Terahertz Range

D. V. Kozlov, V. V. Rumyantsev, A. M. Kadykov, M. A. Fadeev, N. S. Kulikov, V. V. Utochkin, N. N. Mikhailov, S. A. Dvoretskii, V. I. Gavrilenko, H.-W. Hubers, F. Teppe, S. V. Morozov,

https://link.springer.com/article/10.1134%2FS0021364019100114

The terahertz photoluminescence spectra of HgTe/CdHgTe heterostructure with quantum wells under interband optical excitation with a power of 3 to 300 mW have been studied in the temperature range of 30–100 K. The photoluminescence spectrum includes a band corresponding to quantum energies below the width of the band gap. The position of this band does not change with increasing temperature. This property allows attributing it to the capture of holes by acceptor centers. It has been shown that these acceptor centers are singly ionized mercury vacancies, which are double acceptors. A nonmonotonic dependence of the intensity of a signal of a long-wavelength photoluminescence band on the power of an exciting source has been revealed. A short-wavelength photoluminescence band corresponding to interband transitions appears with an increase in the exciting power. It has been shown that this effect is caused by the saturation of the number of partially ionized mercury vacancies with increasing pump intensity.

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-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.

• 
• 
• 
• 
• 
• 

Abstract-Terahertz emission from CdHgTe/HgTe quantum wells with an inverted band structure

• G. Yu. Vasilyeva
• , Yu. L. Ivánov
• , A. O. Zakhar’in
• , A. V. Andrianov
• , L. E. Vorobiev
• , D. A. Firsov
• , M. N. Grigoriev
• , A. V. Antonov
• , A. V. Ikonnikov
• , V. I. Gavrilenko,

• https://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=7575245965608136870

The terahertz electroluminescence from Cd0.7Hg0.3Te/HgTe quantum wells with an inverted band structure in lateral electric fields is experimentally detected and studied. The emission-spectrum maximum for wells 6.5 and 7 nm wide is near 6 meV which corresponds to interband optical transitions. The emission is explained by state depletion in the valence band and conduction band filling due to Zener tunneling, which is confirmed by power-law current–voltage characteristics.

Abstract-Terahertz properties of Dirac fermions in HgTe films with optical doping

V. Dziom, A. Shuvaev, N. N. Mikhailov, A. Pimenov

http://arxiv.org/abs/1603.05926

Terahertz properties of mercury telluride (HgTe) films with critical thickness are presented and discussed. The density of the charge carriers is controlled using contact-free optical doping by visible light. In the magneto-optical response of HgTe the contribution of two types of carriers (electrons and holes) can be identified. The density of the electrons can be modified by light illumination by more than one order of magnitude. As the hole density is roughly illuminationindependent, the terahertz response of the illuminated samples becomes purely electronic. In some cases, light illumination may switch the qualitative electrodynamic response from hole-like to the electron-like. The cyclotron mass of the electrons could be extracted from the data and shows a square root dependence upon the charge concentration in the broad range of parameters. This can be interpreted as a clear proof of a linear dispersion relations, i.e. Dirac-type charge carriers.

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

• 
• 
• 
• 
• 
• 
• 

6 More

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

©2014 American Physical Society