Double Electron–Electron Resonance Between Trapped Electron and Hole in a Semiconductor

We demonstrate the spin interactions between dispersedly trapped electrons and holes in a semiconductor using the double electron–electron resonance (DEER) method of the pulsed electron paramagnetic resonance (EPR) techniques. An aluminum-doped titanium dioxide crystal is adopted as a spin system, in which optically generated electrons and holes are trapped, to reveal EPR signals that appear close to each other at a selected crystal orientation under an external magnetic field. We used the four-pulse DEER method by applying two microwave frequencies to a microwave cavity for pumping electrons and probing holes at the optimum temperature of 32 K. The dipolar modulation in the probed signal by pumping interacting spins was successfully detected. The observed non-oscillating decay shape indicates that the detected interaction is caused by widely distributed trapped electron and hole spins over long distances. We were able to extract a spin-pair distribution function by the first derivative of a background-corrected curve, referring to a previously reported method.     

Strong Effect of the Wavelength of Light on Quantum Oscillations of the Photocurrent and Their Resonant Tunneling Nature in p–i–n GaAs/AlAs Heterostructures

JETP Letters - The strong effect of the wavelength of incident light λ on the fraction of the oscillatory component of the photocurrent in p–i–n GaAs/AlAs heterostructures has been...     

Absorption of Powerful Light by Free Electrons in Crystals: Intraband Electron–Phonon Rabi Oscillations

Optics and Spectroscopy - The absorption of high-power visible or near-IR laser radiation by free electrons is calculated using the modified resonance approximation. The probabilities Wexc of...     

The Electron－Hole Pair in a Single Quantum Dot and That in a Vertically Coupled Quantum Dot

The energy spectra of low-lying states of an exciton in a single and a vertically coupled quantum dots are studied under the influence of a perpendicularly applied magnetic field. Calculations are made by using the method of numerical diagonalization of the Hamiltonian within the effective-mass approximation. We also calculated the binding energy of the ground and the excited states of an exciton in a single quantum dot and that in a vertically coupled quantum dot as a function of the dot radius for different vaJues of the distance and the magnetic field strength.     

Effect of the Radiation Power on the Modification of Oscillations of the Photocurrent in Single-Barrier p–i–n GaAs/AlAs/GaAs Heterostructures with InAs Quantum Dots

JETP Letters - The effect of the power of incident light radiation on the behavior of quantum oscillations of the photocurrent in single-barrier p–i–n GaAs/AlAs heterostructures with...     

Anisotropy of Two-Dimensional Electron and Hole Mobilities in (0 0 1) GaAs/Al x Ga 1− x As Heterostructures Under Uniaxial Stress

Transport properties of two-dimensional electron and hole gas at (0 0 1) GaAs/Al x Ga 1 m x As heterointerface in [1 1 0] and [1 m 1 0] directions have been investigated for the first time under in plane uniaxial compression up to 5 kbar. Resistivity, Shubnikov-de Haas oscillations and Hall effect were measured and carrier densities and mobilities were determined. The in-plane uniaxial compression significantly modifies the energy spectrum of p-GaAs/Al x Ga 1 m x As that leads to strong anisotropy of hole mobility under compression. In the case of the n-type heterostructure uniaxial compression causes only change of the carrier concentration and the corresponding small change of the initial mobility anisotropy, determined by anisotropic surface roughness scattering.     

Interactions between Surface Impurities and the Electron–Hole System of a Semiconductor Crystal

The effects of creation and annihilation of impurities on the surface of a highly doped semiconductor under changes in the surface concentration n of dopant atoms constituting impurities are predicted theoretically. The effects are determined by electrostatic interactions of charged surface impurity species with charge carriers and semiconductor ions. The effects are observed in a certain range of n, provided the surface impurities exhibit donor (acceptor) properties, and the semiconductor is doped with an acceptor (donor) impurity.     

Pair production of J/ψ as a probe of double parton scattering at LHCb

We argue that the recent LHCb observation of J/ψ-pair production indicates a significant contribution from double parton scattering, in addition to the standard single parton scattering component. We propose a method to measure the double parton scattering at LHCb using leptonic final states from the decay of two prompt J/ψ mesons.     

Storage of Photoexcited Electron—Hole Pairs in an AlAs／GaAs Heterostructure Created by Electron Transfer in Real and κ Spaces

The storage of photoexcited electron-hole pairs is experimentally carried out and theoretically realized by transferring electrons in both real and κ spaces through resonant Γ-X in and AlAs/GaAs heterostructure,This is proven by the peculiar capacitance jump and hysteresis in the measured capacitance-voltage curves.Our structure may be used as a photonic memory cell with a long storage time and a fast retrieval of photons as well.     

Effect of Γ–X Intervalley Scattering on the Electron Transport in Double-Barrier GaAs/AlAs(001) Heterostructures

Volt-ampere characteristics, transmission spectra of electrons, and tunneling times are calculated for a three-valley model by the multiband method used for studying the quantum transport in GaAs/AlAs(001) semiconductor heterostructures. The effect of –X intervalley scattering of electrons on the heteroboundaries of the structures is examined.     

Interaction of terahertz radiation with surface and interface plasmon–phonons in AlGaAs/GaAs and GaN/Al2O3 heterostructures

Surface phonon and plasmon–phonon polariton characteristics of GaAs, Al _x Ga_1?x As/GaAs, and GaN/Al₂O₃ layered structures are investigated by means of terahertz radiation reflection spectroscopy. The strong resonant absorption peaks and selective emission of the THz radiation dependent upon the lattice composition and free electron density in these layered structures are experimentally observed and analyzed.     

Spin Glass and Isotropic Negative Magnetoresistance in GaAs–AlGaAs Quantum Wells with a Virtual Anderson Transition

Journal of Experimental and Theoretical Physics - We report on the results of experiments indicating the existence of spin glass in beryllium-doped GaAs–AlGaAs quantum wells with a virtual...     

Influence of the Diagonal and Off-Diagonal Electron–Phonon Interactions on the Formation of Local Polarons and Their Band Structure in Materials with Strong Electron Correlations

For systems with strong electron correlations and strong electron–phonon interaction, we analyze the electron–phonon interaction in local variables. The effects of the mutual influence of electron–electron and electron–phonon interactions that determine the structure of local Hubbard polarons are described. Using a system containing copper–oxygen layers as an example, we consider the competition between the diagonal and off-diagonal interactions of electrons with the breathing mode as the polaron band structure is formed within a corrected formulation of the polaron version of the generalized tight-binding method. The band structure of Hubbard polarons is shown to depend strongly on the temperature due to the excitation of Franck–Condon resonances. For an undoped La₂CuO₄ compound we have described the evolution of the band structure and the spectral function from the hole dispersion in an antiferromagnetic insulator at low temperatures with the valence band maximum at point (π/2, π/2) to the spectrum with the maximum at point (π, π) typical for the paramagnetic phase. The polaron line width at the valence band top and its temperature dependence agree qualitatively with angle-resolved photoemission spectroscopy for undoped cuprates.     

Emission Spectrum and Stability of Two Types of Electron–Hole Liquid in Shallow Si/Si1 – xGexSi Quantum Wells

Physics of the Solid State - Based on calculations within the density functional theory and an analysis of low-temperature photoluminescence spectra, the structure of electron–hole liquid in...     

The Effect of Active Region Heating on Dynamic and Power Characteristics of Quantum Cascade Lasers Emitting at a Wavelength of 4.8 µm at Room Temperature

Optics and Spectroscopy - Results of studying stripe quantum cascade lasers emitting at room temperature in the spectral range of 4.8 µm are presented. Power characteristics and turn-on...     

Electromagnetically Induced Absorption and Transparency Spectra of Degenerate Two-Level Systems with a Strong Coupling Field in Cs Vapour

The electromagnetically induced absorption and electromagnetically induced transparency spectra of degenerate two-level systems with a strong coupling laser were observed. The frequency detuning and intensity effect of the coupling laser were demonstrated simultaneously. A dispersion-like spectrum can be obtained when the coupling laser is situated at blue-side detuning. The absorption inversion was realized when the coupling laser intensity is small. The coherent resonance has a linewidth much narrower than the natural linewidth of the optical transitions.     

Temperature tuning of exciton–photon coupling in a microcavity grown on a (311)A GaAs substrate

We report on the observation of photon-exciton coupling in a MQW microcavity grown on a (311)A GaAs substrate by photoluminescence. This coupling or Rabi splitting was observed by tuning the heavy hole exciton line and the cavity mode by varying the temperature in the range 80–200 K.     

Electron–hole transition in a spherical quantum dot confined at the center of a cylindrical nano-wire: Comparison of isotropic and anisotropic effective mass

Electronic structure of an InAs spherical quantum dot placed at the center of a GaAs cylindrical nano-wire is investigated. The Schrodinger equation within the effective mass approximation is solved and the energy eigenvalues and transition energies are calculated as a function of quantum dot and nano-wire radii using the finite element method. The two types of heavy holes, hhI and hhII, with isotropic and anisotropic effective masses are considered, respectively. The effect of spherical and nano-wire confining potentials, the size of the dot and the nano-wire on ground and first excited state energies of the electron, heavy hole I and heavy hole II are investigated. The results show that the electron and heavy holes energies decrease as the dot and the nano-wire radii increase. The emitted wavelength of transitions between el-hhI and el-hhII are also calculated and compared. The results show that the anisotropy of the effective mass has great effect on the emitted wavelength.     

Linear Interaction (Transformation) of de Broglie Waves of the Γ- and X-Valleys and Intraband Optical Transitions in GaAs/AlAs Quantum-Well Heterostructures in a Lateral Electric Field

We discuss the linear interaction between the de Broglie waves of different electron valleys in heterostructures where a constant electric field is applied along the heterointerfaces (lateral field). The probabilities of phononless and dipole optical transitions of electrons between the - and X-subbands in GaAs/AlAs quantum-well heterosructures with a lateral electric field are calculated. It is shown that the electric field has a strong effect on the probabilities of phononless and direct optical dipole -X electron transitions. Moreover, a lateral electric field changes the spectrum of the intersubband -X light absorption, i.e., there is an intersubband analogue of the Franz-Keldysh effect. The considered linear interaction of de Broglie waves is compared with the well-known cases of linear wave interaction in a magnetized plasma, the Zener breakdown, and the Franz-Keldysh effect in solids.     

Determination of the Efficiency and Energy Transfer Rate in the Fluorescence of a Single Donor–Acceptor Pair Attached to a Biomolecule

Resonance energy transfer from a single donor molecule to a single acceptor molecule (Förster resonance energy transfer) is currently used to determine the microscopic parameters describing interconformational changes in a protein molecule to which this single donor–acceptor pair is attached. A recently developed method makes it possible to intricately search for such parameters using a formula for the efficiency of Förster resonance energy transfer, which is the sum of several Gaussians. Another simpler method for the determination of the desired parameters of interconformational transitions has been proposed in this work on the basis of statistical processing of fluctuating tracks of fluorescence of a single donor–acceptor pair attached to a protein molecule.