arXiv subjects

N. S. Averkiev

Publications and source records attributed to N. S. Averkiev.

51 records · Page 3Linked to original sources

arXiv2010

Non-linear emission spectra of quantum dots strongly coupled to photonic mode

A theory of optical emission of quantum dot arrays in quantum microcavities is developed. The regime of the strong coupling between the quantum dots and photonic mode of the cavity is considered. The quantum dots are modeled as two-level systems. In the low pumping (linear) regime the emission spectra are mainly determined by the superradiant mode where the effective dipoles of the dots oscillate in phase. In the non-linear regime the superradiant mode is destroyed and the emission spectra are sensitive to the parity of quantum dot number. Further increase of the pumping results in the line width narrowing being an evidence of the lasing regime.

cond-mat.mes-hall↗

arXiv2009

Conversion of hole states by acoustic solitons

The hole states in the valence band of a large class of semiconductors are degenerate in the projections of angular momentum. Here we show that the switching of a hole between the states can efficiently be realized by acoustic solitons. The microscopic mechanism of such a state conversion is related to the valence band splitting by local elastic strain. The conversion is studied here for heavy holes localized at shallow and deep acceptors in silicon quantum wells.

cond-mat.mes-hall↗

arXiv2008

Collective modes of quantum dot ensembles in microcavities

Emission spectra of quantum dot arrays in zero-dimensional microcavities are studied theoretically, and it is shown that they are determined by the competition between the formation of the collective superradiant mode and inhomogeneous broadening. The random sources method for the calculation of photoluminescence spectra under a non-resonant pumping is developed, and a microscopic justification of the random sources method within a framework of the standard diagram technique is given. The emission spectra of a microcavity are analyzed with allowance for the spread of exciton states energies caused by an inhomogeneous distribution of quantum dots and a tunneling between them. It is demonstrated that in the case of a strong tunneling coupling the luminescence spectra are sensitive to the geometric positions of the dots, and the collective mode can, under certain conditions, be stabilized by the random tunnel junctions.

cond-mat.mes-hall↗

arXiv2007

Manifestation of spin-orbit interaction in tunneling between 2D electron layers

An influence of spin-orbit interaction on the tunneling between two 2D electron layers is considered. Particular attention is addressed to the relation between the contribution of Rashba and Dresselhaus types. It is shown that without scattering of the electrons, the tunneling conductance can either exhibit resonances at certain voltage values or be substantially suppressed over the whole voltage range. The dependence of the conductance on voltage turns out to be very sensitive to the relation between Rashba and Dresselhaus contributions even in the absence of magnetic field. The elastic scattering broadens the resonances in the first case and restores the conductance to a larger magnitude in the latter one. These effects open possibility to determine the parameters of spin-orbit interaction and electrons scattering time in tunneling experiments with no necessity of external magnetic field.

cond-mat.other↗

arXiv2007

Light-matter interaction in doped microcavities

We discuss theoretically the light-matter coupling in a microcavity containing a quantum well with a two-dimensional electron gas. The high density limit where the bound exciton states are absent is considered. The matrix element of interband optical absorbtion demonstrates the Mahan singularity due to strong Coulomb effect between the electrons and a photocreated hole. We extend the non-local dielectric response theory to calculate the quantum well reflection and transmission coefficients, as well as the microcavity transmission spectra. The new eigenmodes of the system are discussed. Their implications for the steady state and time resolved spectroscopy experiments are analyzed.

cond-mat.mes-hall↗

arXiv2007

Intervalley scattering and weak localization in Si-based two-dimensional structures

We have measured the weak localization magnetoresistance in (001)-oriented Si MOS structures with a wide range of mobilities. For the quantitative analysis of the data, we have extended the theory of weak-localization corrections in the ballistic regime to the system with two equivalent valleys in electron spectrum. This theory describes the observed magnetoresistance and allows the extraction of the phase breaking time tau_phi and the intervalley scattering time tau_v. The temperature dependences tau_phi(T) for all studied structures are in good agreement with the theory of electron-electron interaction effects in two-dimensional systems. The intervalley scattering is elastic and rather strong: tau_v is typically only an order of magnitude greater than the transport time, tau. It is found that the intervalley scattering rate is temperature-independent and the ratio tau_v/tau decreases with increasing the electron density. These observations suggest that the roughness of the Si-SiO2 interface plays the major role in intervalley scattering.

cond-mat.dis-nn↗

arXiv2006

Observation of Spin Relaxation Anisotropy in Semiconductor Quantum Wells

Spin relaxation of two-dimensional electrons in asymmetrical (001) AlGaAs quantum wells are measured by means of Hanle effect. Three different spin relaxation times for spins oriented along [110], [1-10] and [001] crystallographic directions are extracted demonstrating anisotropy of D'yakonov-Perel' spin relaxation mechanism. The relative strengths of Rashba and Dresselhaus terms describing the spin-orbit coupling in semiconductor quantum well structures. It is shown that the Rashba spin-orbit splitting is about four times stronger than the Dresselhaus splitting in the studied structure.

cond-mat.mes-hall↗

arXiv2006

Linear polarization of the photoluminescence of quantum wells

The degree and orientation of the magnetic-field induced linear polarization of the photoluminescence from a wide range of heterostructures containing (Cd,Mn)Te quantum wells between (Cd,Mn,Mg)Te barriers has been studied as a function of detection photon energy, applied magnetic field strength and orientation in the quantum well plane. A theoretical description of this effect in terms of an in-plane deformation acting on the valence band states is presented and is verified by comparison with the experimental data. We attempted to identify clues to the microscopic origin of the valence band spin anisotropy and to the mechanisms which actually determine the linear polarization of the PL in the quantum wells subject to the in-plane magnetic field. The conclusions of the present paper apply in full measure to non-magnetic QWs as well as ensembles of disk-like QDs with shape and/or strain anisotropy.

cond-mat.other↗

arXiv2004

Suppression of spin beats in magneto-oscillation phenomena in two-dimensional electron gas

Theory of magneto-oscillation phenomena has been developed for two-dimensional electron systems with linear-in-k spin splitting. Both Dresselhaus and Rashba contributions are taken into account. It has been shown that the pattern of the magneto-oscillations depends drastically on the ratio between the above terms. The presence of only one type of the k-linear terms gives rise to the beats, i.e. two close harmonics corresponding to the spin-split subbands. However, if the strengths of both contributions are comparable, the third (central) harmonics appears in the spectrum of the magneto-oscillations. For equal strengths of the contributions, only the central harmonic survives, and the oscillations occur at a single frequency, although the k-linear terms remain in the Hamiltonian. Such suppression of the spin beats is studied in detail by the example of the Shubnikov-de Haas effect.

cond-mat.mes-hall↗

arXiv2002

Interference of Spin Splittings in Magneto-Oscillation Phenomena in Two-Dimensional Systems

The spin splitting caused by the terms linear in wavevector in the effective Hamiltonian containing can give rise to the new magneto-oscillation phenomena in two-dimensional systems. It is shown that the joint action of the spin-dependent contributions due to the heterostructure asymmetry and to the lack of inversion center in the bulk material suppresses beats that arise in the magneto-oscillation phenomena in the presence of the terms of only one of these types.

cond-mat.mes-hall↗

arXiv2002

Spin Relaxation Anisotropy in Two-Dimensional Semiconductor Systems

Spin relaxation is investigated theoretically in two-dimensional systems. Various semiconductor structures of both n- and p-types are studied in detail. The most important spin relaxation mechanisms are considered. The spin relaxation times are calculated taking into account the contributions to the spin--orbit interaction due to both the bulk inversion asymmetry and the structure inversion asymmetry. It is shown that in-plane anisotropy of electron spin relaxation appears in III--V asymmetrical heterostructures. This anisotropy may be controlled by external parameters, and the spin relaxation times differ by several orders of magnitude.

cond-mat.mes-hall↗

arXiv2001

Giant Spin Relaxation Anisotropy in Zinc-Blende Heterostructures

Spin relaxation in-plane anisotropy is predicted for heterostructures based on zinc-blende semiconductors. It is shown that it manifests itself especially brightly if the two spin relaxation mechanisms (D'yakonov-Perel' and Rashba) are comparable in efficiency. It is demonstrated that for the quantum well grown along the [0 0 1] direction, the main axes of spin relaxation rate tensor are [1 1 0] and [1 -1 0].

cond-mat.mes-hall↗

arXiv2001

Effect of intersubband scattering on weak localization in 2D systems

The theory of weak localization is generalized for multilevel 2D systems taking into account intersubband scattering. It is shown that weak intersubband scattering which is negligible in a classical transport, affects strongly the weak-localization correction to conductivity. The anomalous magnetoresistance is calculated in the whole range of classically low magnetic fields. This correction to conductivity is shown to depend strongly on the ratios of occupied level concentrations. It is demonstrated that at relatively low population of the excited subband, it is necessary to use the present theory because the high-field limit asimptotics is shown to be achieved only in classical magnetic fields.

cond-mat.mes-hall↗

arXiv2000

Spin relaxation in asymmetrical heterostructures

Electron spin relaxation caused by the D'yakonov-Perel' mechanism is investigated theoretically in asymmetrical A$_3$B$_5$ heterostructures. The total spin relaxation anisotropy is demonstrated for a wide range of structure parameters and temperatures. The spin relaxation rates dependences are derived for GaAs-based heterojunction and triangular quantum well. The calculations show a few orders of magnitude difference in spin relaxation times.

cond-mat.mes-hall↗

arXiv1999

Weak localisation in AlGaAs/GaAs p-type quantum wells

We have for the first time experimentally investigated the weak localisation magnetoresistance in a AlGaAs/GaAs p-type quantum well. The peculiarity of such systems is that spin-orbit interaction is strong. On the theoretical side it is not possible to treat the spin-orbit interaction as a perturbation. This is in contrast to all prior investigations of weak localisation. In this letter we compare the experimental results with a newly developed diffusion theory, which explicitly describes the weak localisation regime when the spin-orbit coupling is strong. The spin relaxation rates calculated from the fitting parameters was found to agree with theoretical expectations. Furthermore the fitting parameters indicate an enhanced phase breaking rate compared to theoretical predictions.

cond-mat.mes-hall↗