arXiv subjects

E. L. Ivchenko

Publications and source records attributed to E. L. Ivchenko.

At least 73 records · Page 4Linked to original sources

arXiv2014

Effect of carrier heating on photovoltage in FET

We have calculated, within the framework of the Boltzmann equation, a dc electric current and emf in a two-dimensional system induced by the high-frequency field of an electromagnetic wave or the electric field of a plasmon wave. It is established that the generated current consists of two contributions, one of which is proportional to the real part of the wave vector projection of the exciting wave onto the interface plane and represents the electron drag effect, and the other contribution is proportional to the extinction coefficient of the wave in the interface plane. It is shown that the main cause of the second contribution is a nonuniform electron heating created by the wave and controlled by the energy relaxation time of the electron gas. In FET the heating mechanism of the electric-current formation can remarkably exceed the current calculated neglecting the heating.

cond-mat.mes-hall↗

arXiv2014

Spin-flip Raman scattering of the $Γ$-X mixed exciton in indirect band-gap (In,Al)As/AlAs quantum dots

The band structure of type-I (In,Al)As/AlAs quantum dots with band gap energy exceeding 1.63 eV is indirect in momentum space, leading to long-lived exciton states with potential applications in quantum information. Optical access to these excitons is provided by mixing of the $Γ$- and X-conduction band valleys, from which control of their spin states can be gained. This access is used here for studying the exciton spin-level structure by resonant spin-flip Raman scattering, allowing us to accurately measure the anisotropic hole and isotropic electron $g$ factors. The spin-flip mechanisms for the indirect exciton and its constituents as well as the underlying optical selection rules are determined. The spin-flip intensity is a reliable measure of the strength of $Γ$-X-valley mixing, as evidenced by both experiment and theory.

cond-mat.mes-hall↗

arXiv2014

Spin dynamics in semiconductors in the streaming regime

We present results of a cross-disciplinary theoretical research at the interface of spin physics and hot-electron transport. A moderately strong electric field is assumed to provide the streaming regime where each free charge carrier, an electron or a hole, accelerates quasiballistically in the "passive" region until reaching the optical-phonon energy, then emits an optical phonon and starts the next period of acceleration. The inclusion of spin degree of freedom into the streaming-regime kinetics gives rise to rich and interesting spin-related phenomena. Firstly, in the streaming regime the spin relaxation is substantially modified, and the current-induced spin orientation is remarkably increased. Under short-pulsed photoexcitation at the bottom of conduction band the photoelectrons execute a periodic damped motion in the energy space with the period equal to the free flight time of an electron in the passive region. If the short optical pulse is circularly polarized so that the photocarriers are spin oriented, then the spin energy distribution is oscillating in time as well, which can be detected in the pump-probe time-resolved experiments. We show that the spin-orbit splitting of the conduction band becomes a source for additional spin oscillations, periodic or aperiodic depending on the value of electric field.

cond-mat.mes-hall↗

arXiv2014

Spin noise spectroscopy of a single-quantum-well microcavity

We report on the first experimental observation of spin noise in a single semiconductor quantum well embedded into a microcavity. The great cavity-enhanced sensitivity to fluctuations of optical anisotropy has allowed us to measure the Kerr rotation and ellipticity noise spectra in the strong coupling regime. The spin noise spectra clearly show two resonant features: a conventional magneto-resonant component shifting towards higher frequencies with magnetic field and an unusual "nonmagnetic" component centered at zero frequency and getting suppressed with increasing magnetic field. We attribute the first of them to the Larmor precession of free electron spins, while the second one being presumably due to hyperfine electron-nuclei spin interactions.

cond-mat.mes-hall↗

arXiv2013

Spin-orbit splitting of valence subbands in semiconductor nanostructures

We propose the 14-band $\mathbf k \cdot \mathbf p$ model to calculate spin-orbit splittings of the valence subbands in semiconductor quantum wells. The reduced symmetry of quantum well interfaces is incorporated by means of additional terms in the boundary conditions which mix the $Γ_{15}$ conduction and valence Bloch functions at the interfaces. It is demonstrated that the interface-induced effect makes the dominating contribution to the heavy-hole spin splitting. A simple analytical expression for the interface contribution is derived. In contrast to the 4$\times$4 effective Hamiltonian model, where the problem of treating the $V_z k_z^3$ term seems to be unsolvable, the 14-band model naturally avoids and overcomes this problem. Our results are in agreement with the recent atomistic calculations [J.-W. Luo et al., Phys. Rev. Lett. {\bf 104}, 066405 (2010)].

cond-mat.mes-hall↗

arXiv2013

Radiative topological states in resonant photonic crystals

We present a theory of topological edge states in one-dimensional resonant photonic crystals with a compound unit cell. Contrary to the traditional electronic topological states the states under consideration are radiative, i.e., they decay in time due to the light escape through the structure boundaries. We demonstrate that the states survive despite their radiative decay and can be detected both in time- and frequency-dependent light reflection.

cond-mat.mes-hall↗

arXiv2013

Effect of exchange interaction on the spin fluctuations of localized electrons

In this paper a microscopic theory of spin fluctuations in an ensemble of electrons localized on donors in a bulk semiconductor has been developed. Both the hyperfine interaction of the electron spin with spins of lattice nuclei and the exchange interaction between the electrons have been taken into account. We propose a model of clusters to calculate spin noise spectra of the ensemble of localized charge carriers. It has been shown that the electron-electron exchange interaction leads to an effective averaging of random nuclear fields and a shift of the peak in the spin-fluctuation spectrum towards lower frequencies.

cond-mat.mes-hall↗

arXiv2013

Spin-dependent phenomena in semiconductors in strong electric fields

We develop a theory of spin-dependent phenomena in the streaming regime characterized by ballistic acceleration of electrons in the moderate electric field until they achieve the optical phonon energy and abruptly emit the phonons. It is shown that the Dyakonov-Perel spin relaxation is drastically modified in this regime, the current-induced spin orientation remarkably increases, reaches a high value ~2% in the electric field ~1kV/cm and falls with the further increase in the field. The spin polarization enhancement is caused by squeezing of the electron momentum distribution in the direction of drift. We also predict field-induced oscillatory dynamics of spin polarization of the photocarriers excited into the conduction band by a short circularly-polarized optical pulse.

cond-mat.mes-hall↗

arXiv2013

Spin-dependent inter- and intra-valley electron-phonon scattering in germanium

We investigate the spin-dependent electron-phonon scatterings of the $L$ and $Γ$ valleys and the band structure near the conduction band minima in germanium. We first construct a $16\times16$ ${\bm k}\cdot{\bm p}$ Hamiltonian in the vicinity of the $L$ point in germanium, which ensures the correctness of the band structure of the lowest three conduction bands and highest two valence bands. This Hamiltonian facilitates the analysis of the spin-related properties of the conduction electrons. We then demonstrate the phonon-induced electron scatterings of the $L$ and $Γ$ valleys, i.e., the intra-$Γ$/ $L$ valley, inter--$Γ$-$L$ valley and inter--$L$-$L$ valley scatterings in germanium. The selection rules and complete scattering matrices for these scatterings are calculated, where the scattering matrices for the intra-$Γ$ valley scattering, inter--$Γ$-$L$ valley scattering and the optical-phonon and the separated transverse-acoustic- and longitudinal-acoustic-phonon contributions to the intra-$Γ$ valley scattering have not been reported in the literature. The coefficients in these scattering matrices are obtained via the pseudo-potential calculation, which also verifies our selection rules and wave-vector dependence. We further discuss the Elliott-Yafet mechanisms in these electron-phonon scatterings with the ${\bm k}$$\cdot$${\bm p}$ eigenstates at the $L$ and $Γ$ valleys. Our investigation of these electron-phonon scatterings are essential for the study of the optical orientation of spin and hot-electron relaxation in germanium.

cond-mat.mtrl-sci↗

arXiv2012

Magnetic field induced valence band mixing in [111] grown semiconductor quantum dots

We present a microscopic theory of the magnetic field induced mixing of heavy-hole states +/- 3/2 in GaAs droplet dots grown on (111)A substrates. The proposed theoretical model takes into account the striking dot shape with trigonal symmetry revealed in atomic force microscopy. Our calculations of the hole states are carried out within the Luttinger Hamiltonian formalism, supplemented with allowance for the triangularity of the confining potential. They are in quantitative agreement with the experimentally observed polarization selection rules, emission line intensities and energy splittings in both longitudinal and transverse magnetic fields for neutral and charged excitons in all measured single dots.

cond-mat.mes-hall↗

arXiv2012

Spin noise in quantum dot ensembles

We study theoretically spin fluctuations of resident electrons or holes in singly charged quantum dots. The effects of external magnetic field and effective fields caused by the interaction of electron and nuclei spins are analyzed. The fluctuations of spin Faraday, Kerr and ellipticity signals revealing the spin noise of resident charge carriers are calculated for the continuous wave probing at the singlet trion resonance.

cond-mat.mes-hall↗

arXiv2012

Ratchet effects in two-dimensional systems with a lateral periodic potential

Radiation-induced ratchet electric currents have been studied theoretically in graphene with a periodic noncentrosymmetric lateral potential. The ratchet current generated under normal incidence is shown to consist of two contributions, one of them being polarization-independent and proportional to the energy relaxation time, and another controlled solely by elastic scattering processes and sensitive to both the linear and circular polarization of radiation. Two realistic mechanisms of electron scattering in graphene are considered. For short-range defects, the ratchet current is helicity-dependent but independent of the direction of linear polarization. For the Coulomb impurity scattering, the ratchet current is forbidden for the radiation linearly polarized in the plane perpendicular to the lateral-potential modulation direction. For comparison, the ratchet currents in a quantum well with a lateral superlattice are calculated at low temperatures with allowance for the dependence of the momentum relaxation time on the electron energy.

cond-mat.mes-hall↗

arXiv2011

Giant Zeeman splitting of light holes in GaAs/AlGaAs quantum wells

We have developed a theory of the longitudinal $g$ factor of light holes in semiconductor quantum wells. It is shown that the absolute value of the light-hole $g$-factor can strongly exceed its value in the bulk and, moreover, the dependence of the Zeeman splitting on magnetic field becomes non-linear in relatively low fields. These effects are determined by the proximity of the ground light-hole subband, $lh1$, to the first excited heavy-hole subband, $hh2$, in GaAs/AlGaAs-type structures. The particular calculations are performed in the framework of Luttinger Hamiltonian taking into account both the magnetic field-induced mixing of $lh1$ and $hh2$ states and the mixing of these states at heterointerfaces, the latter caused by chemical bonds anisotropy. A theory of magneto-induced reflection and transmission of light through the quantum wells for the light-hole-to-electron absorption edge is also presented.

cond-mat.mes-hall↗

arXiv2011

Terahertz radiation driven chiral edge currents in graphene

We observe photocurrents induced in single layer graphene samples by illumination of the graphene edges with circularly polarized terahertz radiation at normal incidence. The photocurrent flows along the sample edges and forms a vortex. Its winding direction reverses by switching the light helicity from left- to right-handed. We demonstrate that the photocurrent stems from the sample edges, which reduce the spatial symmetry and result in an asymmetric scattering of carriers driven by the radiation electric field. The developed theory is in a good agreement with the experiment. We show that the edge photocurrents can be applied for determination of the conductivity type and the momentum scattering time of the charge carriers in the graphene edge vicinity.

cond-mat.mes-hall↗

arXiv2011

Spin orientation by electric current in (110) quantum wells

We develop a theory of spin orientation by electric current in (110)-grown semiconductor quantum wells. The controversy in the factor of two from two existed approaches is resolved by pointing out the importance of energy relaxation in this problem. The limiting cases of fast and slow energy relaxation relative to spin relaxation are considered for asymmetric (110) quantum wells. For symmetricly-doped structures the effect of spin orientation is shown to exist due to spatial fluctuations of the Rashba spin-orbit splitting. We demonstrate that the spin orientation depends strongly on the correlation length of these fluctuations as well as on the ratio of the energy and spin relaxation rates. The time-resolved kinetics of spin polarization by electric current is also governed by the correlation length being not purely exponential at slow energy relaxation. Electrical spin orientation in two-dimensional topological insulators is calculated and compared with the spin polarization induced by the magnetic field.

cond-mat.mes-hall↗

arXiv2011

Dark-bright mixing of interband transitions in symmetric semiconductor quantum dots

In photoluminescence spectra of symmetric [111] grown GaAs/AlGaAs quantum dots in longitudinal magnetic fields applied along the growth axis we observe in addition to the expected bright states also nominally dark transitions for both charged and neutral excitons. We uncover a strongly non-monotonous, sign changing field dependence of the bright neutral exciton splitting resulting from the interplay between exchange and Zeeman effects. Our theory shows quantitatively that these surprising experimental results are due to magnetic-field-induced \pm 3/2 heavy-hole mixing, an inherent property of systems with C_3v point-group symmetry.

cond-mat.mes-hall↗

arXiv2011

Purcell effect in small metallic cavities

We have studied theoretically the Purcell factor which characterizes a change in the emission rate of an electric or magnetic dipole embedded in the center of a spherical cavity. The main attention is paid to the analysis of cavities with radii small compared to the wavelength. It is shown that the Purcell factor in small metallic cavities varies in a wide range depending on the ratio of the cavity size to the skin depth.

cond-mat.mes-hall↗

arXiv2011

Classical ratchet effects in heterostructures with a lateral periodic potential

We study terahertz radiation induced ratchet currents in low dimensional semiconductor structures with a superimposed one-dimensional lateral periodic potential. The periodic potential is produced by etching a grating into the sample surface or depositing metal stripes periodically on the sample top. Microscopically, the photocurrent generation is based on the combined action of the lateral periodic potential, verified by transport measurements, and the in-plane modulated pumping caused by the lateral superlattice. We show that a substantial part of the total current is caused by the polarization-independent Seebeck ratchet effect. In addition, polarization-dependent photocurrents occur, which we interpret in terms of their underlying microscopical mechanisms. As a result, the class of ratchet systems needs to be extended by linear and circular ratchets, sensitive to linear and circular polarizations of the driving electro-magnetic force.

cond-mat.mes-hall↗