38 research outputs found
Cyclotron Resonance Assisted Photocurrents in Surface States of a 3D Topological Insulator Based on a Strained High Mobility HgTe Film
We report on the observation of cyclotron resonance induced photocurrents,
excited by continuous wave terahertz radiation, in a 3D topological insulator
(TI) based on an 80 nm strained HgTe film. The analysis of the photocurrent
formation is supported by complimentary measurements of magneto-transport and
radiation transmission. We demonstrate that the photocurrent is generated in
the topologically protected surface states. Studying the resonance response in
a gated sample we examined the behavior of the photocurrent, which enables us
to extract the mobility and the cyclotron mass as a function of the Fermi
energy. For high gate voltages we also detected cyclotron resonance (CR) of
bulk carriers, with a mass about two times larger than that obtained for the
surface states. The origin of the CR assisted photocurrent is discussed in
terms of asymmetric scattering of TI surface carriers in the momentum space.
Furthermore, we show that studying the photocurrent in gated samples provides a
sensitive method to probe the effective masses and the mobility of 2D Dirac
surface states, when the Fermi level lies in the bulk energy gap or even in the
conduction band
Impact ionization induced by terahertz radiation in HgTe quantum wells of critical thickness
We report on the observation of terahertz (THz) radiation induced
band-to-band impact ionization in \HgTe quantum well (QW) structures of
critical thickness, which are characterized by a nearly linear energy
dispersion. The THz electric field drives the carriers initializing
electron-hole pair generation. The carrier multiplication is observed for
photon energies less than the energy gap under the condition that the product
of the radiation angular frequency and momentum relaxation time
larger than unity. In this case, the charge carriers acquire
high energies solely because of collisions in the presence of a high-frequency
electric field. The developed microscopic theory shows that the probability of
the light impact ionization is proportional to , with the
radiation electric field amplitude and the characteristic field parameter
. As observed in experiment, it exhibits a strong frequency dependence for
characterized by the characteristic field linearly
increasing with the radiation frequency
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
Symmetry breaking and circular photogalvanic effect in epitaxial CdxHg1-xTe films
We report on the observation of symmetry breaking and the circular photogalvanic effect in CdxHg1-xTe alloys. We demonstrate that irradiation of bulk epitaxial films with circularly polarized terahertz radiation leads to the circular photogalvanic effect (CPGE) yielding a photocurrent whose direction reverses upon switching the photon helicity. This effect is forbidden in bulk zinc-blende crystals by symmetry arguments; therefore, its observation indicates either the symmetry reduction of bulk material or that the photocurrent is excited in the topological surface states formed in a material with low cadmium concentration. We show that the bulk states play a crucial role because the CPGE was also clearly detected in samples with noninverted band structure. We suggest that strain is a reason for the symmetry reduction. We develop a theory of the CPGE showing that the photocurrent results from the quantum interference of different pathways contributing to the free-carrier absorption (Drude-like) of monochromatic radiation
Development of the Market of Themed Hotels with Historical Interior Style in Russia
Π Π°ΡΡΠΌΠ°ΡΡΠΈΠ²Π°ΡΡΡΡ ΠΏΡΠΈΠΌΠ΅ΡΡ ΡΠ΅ΠΌΠ°ΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΎΡΠ΅Π»Π΅ΠΉ Ρ ΠΈΡΡΠΎΡΠΈΡΠ΅ΡΠΊΠΈΠΌ ΡΡΠΈΠ»Π΅ΠΌ ΠΈΠ½ΡΠ΅ΡΡΠ΅ΡΠ° Π² ΠΠ²ΡΠΎΠΏΠ΅ ΠΈ Π ΠΎΡΡΠΈΠΈ, ΠΈΠ·ΡΡΠ°Π΅ΡΡΡ Π²ΠΎΠ·ΠΌΠΎΠΆΠ½ΠΎΡΡΡ ΡΠ°Π·Π²ΠΈΡΠΈΡ ΡΡΠ½ΠΊΠ° ΡΠ΅ΠΌΠ°ΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΎΡΠ΅Π»Π΅ΠΉ Π² ΠΈΡΡΠΎΡΠΈΡΠ΅ΡΠΊΠΎΠΌ ΡΡΠΈΠ»Π΅ Π² Π ΠΎΡΡΠΈΠΈ. ΠΠ° ΡΠΎΠ²ΡΠ΅ΠΌΠ΅Π½Π½ΠΎΠΌ ΡΡΠ°ΠΏΠ΅ ΡΠ°Π·Π²ΠΈΡΠΈΡ Π³ΠΎΡΡΠΈΠ½ΠΈΡΠ½ΠΎΠΉ ΠΈΠ½Π΄ΡΡΡΡΠΈΠΈ ΠΎΠ΄Π½ΠΈΠΌ ΠΈΠ· ΡΡΠ΅Π½Π΄ΠΎΠ² ΡΡΠ°Π½ΠΎΠ²ΠΈΡΡΡ ΡΡΡΠ΅ΠΌΠ»Π΅Π½ΠΈΠ΅ ΠΏΡΠ΅Π΄Π»ΠΎΠΆΠΈΡΡ ΠΏΠΎΡΡΠ΅Π±ΠΈΡΠ΅Π»Ρ ΠΎΡΠΈΠ³ΠΈΠ½Π°Π»ΡΠ½ΡΠΉ Π³ΠΎΡΡΠΈΠ½ΠΈΡΠ½ΡΠΉ ΠΏΡΠΎΠ΄ΡΠΊΡ. ΠΡΡΠ²Π»Π΅Π½ΠΈΠ΅ ΠΏΠ΅ΡΡΠΏΠ΅ΠΊΡΠΈΠ² ΡΠ°Π·Π²ΠΈΡΠΈΡ ΡΠ΅ΠΌΠ°ΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΎΡΠ΅Π»Π΅ΠΉ Π½Π° ΡΠ΅ΡΡΠΈΡΠΎΡΠΈΠΈ Π ΠΎΡΡΠΈΠΈ ΡΠ²Π»ΡΠ΅ΡΡΡ Π·Π°Π΄Π°ΡΠ΅ΠΉ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ, Π² ΡΠ°ΠΌΠΊΠ°Ρ
ΠΊΠΎΡΠΎΡΠΎΠ³ΠΎ Π±ΡΠ» ΠΏΡΠΎΠ²Π΅Π΄Π΅Π½ ΠΎΠΏΡΠΎΡ, ΠΏΠΎΠΊΠ°Π·Π°Π²ΡΠΈΠΉ, ΡΡΠΎ ΡΠ°Π·Π²ΠΈΡΠΈΠ΅ ΡΡΠ½ΠΊΠ° ΡΠ΅ΠΌΠ°ΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΎΡΠ΅Π»Π΅ΠΉ β ΠΎΠ΄ΠΈΠ½ ΠΈΠ· ΡΠ°ΠΊΡΠΎΡΠΎΠ² ΠΏΠΎΠ²ΡΡΠ΅Π½ΠΈΡ ΡΡΡΠΈΡΡΡΠΊΠΎΠΉ ΠΏΡΠΈΠ²Π»Π΅ΠΊΠ°ΡΠ΅Π»ΡΠ½ΠΎΡΡΠΈ ΡΠΎΠ³ΠΎ ΠΈΠ»ΠΈ ΠΈΠ½ΠΎΠ³ΠΎ ΡΠ΅Π³ΠΈΠΎΠ½Π°.This article explores the concepts of image and corporate identity, considers the most striking examples of themed hotels with a historical interior style in Europe and Russia, and explores the possibility of developing a market for themed hotels in a historical style in Russia. At the present stage of development of the hotel industry, one of the trends is the desire to offer the consumer an original hotel product.Identifying the prospects for the development of themed hotels in Russia is the task of the study, in which a survey was conducted, which showed that the development of the market of themed hotels is one of the factors of increasing the tourist attractiveness of a particular region