Exciton binding energy in CdMnTe crystals

We report some results of magnetoabsorption and magnetoreflectivity measurements performed on CdMnTe crystals in magnetic field up to 30 T. The exciton energy at low fields in materials containing magnetic ions is calculated on the basis of the Altarelli-Lipari model and compared with the experimental results. It is shown that spin mixing in degenerate bands strongly affects magnetoabsorption.     

Giant radiofrequency magnetoabsorption in La0.5Sr0.5CoO3 cobaltite

Giant radiofrequency magnetoabsorption in La_0.5Sr_0.5CoO₃ polycrystalline lanthanum cobaltite is studied in the temperature interval 77–300 K and 0.5–12.5 MHz frequency range. The specimen’s Curie temperature T _C is about 250 K. The magnetoabsorption is found to increase with decreasing frequency, reaching 58% at f = 0.5 MHz near the Curie temperature. The results are satisfactorily explained based on the known physical ideas of high-frequency wave absorption in magnetic materials. The effects of giant magnetoabsorption and rapid variation of the absorption near the Curie temperature can be used in radiofrequency sensors of the magnetic field and temperature.     

Measurement of the miniband width in a superlattice with interband absorption in a magnetic field parallel to the layers

Interband magnetoabsorption measurements of a superlattice with GaAs/ GaAlAs layers, thin compared to the cyclotron radius, in a magnetic field parallel to the layers show interband Landau level transitions exclusively for radiation energies falling within the hole and the electron subband width. The data are quantitatively explained with energy levels of a Kronig-Penney model in a parallel magnetic field, and permit a direct observation of the superlattice bandwidth.     

磁场中窄禁带半导体的高阶光学性质(Ⅰ)

本文计算了在磁场中,窄禁带半导体的能级和波函数、双光子跃迁的选择定则以及双光子磁吸收系数,并将计算结果与实验进行了比较。 关键词：     

Effect of dimensional and magnetic quantization hybridization in the optical absorption spectra of nanoheterosystems with <Emphasis Type="Italic">D</Emphasis><Superscript>(−)</Superscript>-states

The magnetoabsorption of light by quantum dot — D^(–)-center complexes synthesized in a transparent dielectric matrix — is theoretically studied with allowance for dispersed quantum dot (QD) sizes. In the effective mass approximation, an analytical expression for the impurity magnetoabsorption coefficient of light polarized in the quantizing magnetic polarization field direction is derived.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 67–72, October, 2004.     

Determination of the band structure parameters of Cd0.95Mn0.05Se from magnetoabsorption measurements

Band parameters and the exchange integrals of Cd_0.95Mn_0.05Se are evaluated using magnetoabsorption measurement results. The anisotropy of the exchange interaction for valence band electrons and the magnetic field dependent wave function mixing coefficients are obtained. The use of a quasi-cubic model for describing a CdMnSe crystal in the presence of magnetic field is shown to be unjustified.     

Fano-type features in magnetoabsorption in semiconductors

It is shown that bulk semiconductors exhibit strongly asymmetric Fano-type resonance profiles in magnetoabsorption processes involving the formation of hot electron-hole pairs (EHPs) and accompanied by the scattering of the EHPs by defects. This result is valid for transitions to electronic states with large Landau quantum numbers, when the Coulomb interaction plays a small role. The physical reason for such a sharp change in the magnetoabsorption coefficient as compared with the expected result for the ordinary density of states in a quantizing magnetic field is that the electronic excitations are quasi-one-dimensional. The form of the resonance absorption is in good qualitative agreement with the experimental data. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 8, 619–622 (25 April 1996)     

Influence of an electric field on the magnetoabsorption in a field of resonant laser radiation

The frequency dependence of the coefficient of interband magnetoabsorption of a weak electromagnetic wave propagating in a constant electric field and in a field of resonant laser radiation at a frequency equal to the cyclotron frequency (infrared magnetic resonance) is calculated. The specific features observed in interband absorption of the electromagnetic wave in a uniform electric field are considered for the case in which the frequency of laser radiation is equal to the confinement frequency in a parabolic quantum well (infrared quantum-well resonance).     

Microwave magnetoabsorption in the CeAl<Subscript>2</Subscript> magnetic Kondo lattice at low temperatures

The magnetic phase diagram of the CeAl₂ magnetic Kondo lattice was studied using microwave magnetoabsorption spectroscopy at frequencies of 37–118 GHz, temperatures of 1.8–4.6 K, and magnetic fields of up to 70 kOe. The observed anomalies in magnetoabsorption, when combined with the change in the carrier scattering pattern in (established in galvanomagnetic measurements) CeAl₂ near H*≈35 kOe at liquid-helium temperatures, suggest that this compound undergoes a sequence of magnetic transitions accompanied by strong spin fluctuations. The nature of the magnetic phases and the mechanisms driving the phase transformations in CeAl₂ are discussed.     

Defect-Related Photoresponse and Polarization-Sensitive Photodetection of Single ZnO Nanowires

Defect-related photoconductivity of single ZnO nanowires is investigated. The photoconductivity shows powerlaw dependence with incident green laser intensity due to the defect mechanisms including both recombination centres and traps. The device based on single ZnO nanowire shows a sensitive photoresponse to green light with significant on/off ratios. In addition, the photocurrent ＆ highly sensitive to the polarization of the incident illumination. Therefore, the nanowire may act as a polarized photodetector.     

Ferroelectric,magnetoelectric and photoelectric properties of BiFeO3 /LaNiO3 heterostructure

BiFeO₃/LaNiO₃ (BFO/LNO) heterostructure was fabricated on quartz substrate via RF sputtering method. The microstructure and surface morphology of the BFO/LNO heterostructure was demonstrated. BFO layer shows good ferroelectric and weak ferromagnetic characters at room temperature. The dielectric constants of the heterostructure under an applied magnetic field 1.2T and zero field are both decreased with increasing frequency at room temperature and the dielectric constant under the applied magnetic field is larger, which is attributed to the coupling between the electric and magnetic dipoles, and further demonstrated in the framework of the Ginzburg-Landau theory for second phase transition. Additionally, the photoconductivity of the heterostructure under blue-laser illumination was observed, and the photoconductivity increase with the enhanced power of the blue-laser.     

Theory of exciton effects in the high-field magnetoabsorption of real semiconductors

Direct exciton states of cubic semiconductors in a high magnetic field are investigated taking into full account the degeneracy and anisotropy of the valence bands. The adiabatic method is used to decouple the components of the motion parallel and perpendicular to the magnetic field. One-dimensional Hamiltonians are obtained analytically for the various exciton states and selection rules for optical transitions are discussed. Accurate numerical values of the energy levels are given for H parallel to the (110) direction. The results obtained provide the first quantitative interpretation of the fine structure observed in high resolution measurements of magnetoabsorption in Ge.     

Far infrared resonant magnetoabsorption in low density Si inversion layers

The density and temperature dependences of high frequency/resonant field (61.3 cm^-1, 11T) resonant magnetoabsorption data in (100) Si inversion layers at low densities are strikingly different from those observed at lower frequencies/fields. The results, which include a dramatic resonant line narrowing at high fields, are discussed in light of single-electron localization and the possibility of a cooperative electronic transition assisted by the large magnetic field.     

Magnetospectroscopy of double HgTe/CdHgTe QWs with inverted band structure in high magnetic fields up to 30 T

Magnetoabsorption in far and mid IR ranges in double HgTe/CdHgTe quantum wells with inverted band structure has been studied in high magnetic fields up to 30 T. Numerous intraband and interband transitions have been revealed in the spectra and interpreted within axial 8 × 8 k·p model. Splitting of dominant magnetoabsorption lines resulting from optical transitions from hole-like zero-mode Landau level has been discovered and discussed in terms of a built-in electric field and collective phenomena.     

Shallow acceptor levels in Ge/GeSi heterostructures with quantum wells in a magnetic field

Shallow acceptors in Ge/GeSi heterostructures with quantum wells are studied theoretically and experimentally in the presence of a magnetic field. It is shown that, in addition to the cyclotron resonance lines, magnetoabsorption spectra reveal transitions from the acceptor ground state to excited states related to Landau levels from the first and second confinement subbands, as well as the resonances caused by ionization of A⁺ centers.     

Terahertz Spectroscopy of Two-Dimensional Semimetal in Three-Layer InAs/GaSb/InAs Quantum Well

JETP Letters - The features of terahertz photoluminescence and magnetoabsorption in magnetic fields up to 16 T in threelayer InAs/GaSb/InAs quantum wells with a band structure corresponding to a...     

Microwave-induced magnetic field state with zero conductivity in GaAs/AlAs Corbino disks and hall bars

The microwave photoconductivity of the 2D electron gas in GaAs/AlAs heterostructures has been investigated at a temperature of 4.2 K in magnetic fields up to 1.5 T. It has been found that the magnetic field state with zero conductivity appears in GaAs/AlAs Corbino disks irradiated by 130.70-GHz microwave radiation. This state was previously observed only in GaAs/AlGaAs Corbino disks with much higher electron mobility and lower density. It has been shown that the microwave photoconductivity measured in high magnetic fields on Corbino disks can significantly differ from the value calculated from the results of the measurements on Hall bars. This difference is explained by the fact that the conditions of the appearing magnetoplasmons that affect the magnitude and character of the microwave photoconductivity (photoresistance) in the Corbino disks are nonequivalent to those in the Hall bars.     

Impact ionization induced negative far-infrared photoconductivity inn-GaAs

Far-infrared photoconductivity ofn-GaAs epitaxial layers showing impact ionization breakdown has been investigated by molecular lasers at photon energies below the 1s-2p shallow donor transition energy. Negative photoconductivity was observed if a magnetic field was applied to the crystals and if impact ionization of donors by the electric bias field was the dominant electron excitation mechanism. The experimental results are qualitatively explained on the basis of the generation-recombination kinetics of electrons bound to donors. Negative photoconductivity is attributed to optically induced free to bound transitions of electrons from theN=0 Landau band to donor levels shifted by the magnetic field above the low energy edge of the conduction band.     

Magnetic quantum oscillations in the photovoltaic effect of Cd0.24Hg0.76Te

The first experimental evidence of magnetic quantum oscillations in the photovoltaic effect is reported. Experiments were carried out with the p?n junction in Cd_0.24Hg_0.76Te placed in a quantizing magnetic field. The oscillations are related with the interband Γ₈ → Γ₆ magnetoabsorption transmissions. The discrepancy between experimental data and theory is explained by the effect of the p?n junction electric field on the magneto- absorption behaviour.     

Influence of electric current and magnetic field on terahertz photoconductivity in Pb1 − x Sn x Te(In)

Photoconductivity of Pb_{1 ? x} Sn _x Te(In) solid solutions in the terahertz spectral range is defined by a new type of local electron states linked to the quasi-Fermi level. The paper deals with investigation of the influence of electric current and magnetic field on the amplitude of the terahertz photoconductivity in Pb_{1 ? x} Sn _x Te(In) alloys of different composition. It is shown that the density of local electron states responsible for the positive persistent photoconductivity decreases with increasing electric current via a sample, as well as with transition to the hole conductivity in samples with a high content of tin telluride (x > 0.26). It is found that the magnetic field dependence of the positive photoconductivity is non-monotonous and has a maximum. The maximum position in magnetic field is proportional to the terahertz radiation quantum energy. Mechanisms responsible for the effects observed are discussed.