arXiv subjects

D. S. Smirnov

Publications and source records attributed to D. S. Smirnov.

At least 55 records · Page 3Linked to original sources

arXiv2019

Universal power law decay of spin polarization in double quantum dot

We study the spin dynamics and spin noise in a double quantum dot taking into account the interplay between hopping, exchange interaction and the hyperfine interaction. At short time scales the spin relaxation is governed by the spin dephasing in the random nuclear fields. At long time scales the spin polarization obeys universal power law $1/t$ independent of the relation between all the parameters of the system. This effect is related to the competition between the spin blockade effect and the hyperfine interaction. The spin noise spectrum of the system universally diverges as $\ln(1/ω)$ at low frequencies.

cond-mat.mes-hall↗

arXiv2018

Hyperfine interaction in atomically thin transition metal dichalcogenides

Localization of charge carriers in monolayers (MLs) of transition metal dichalcogenides (TMDs) dramatically increases spin and valley coherence times, and, by analogy with other systems, the role of the hyperfine interaction should enhance. We perform theoretical analysis of the intervalley hyperfine interaction in TMD MLs based on the group representation theory. We demonstrate, that the spin-valley locking leads to the helical structure of the in-plane hyperfine interaction. In the upper valence band the hyperfine interaction is shown to be of the Ising type, which can be used for fabrication of the atomically thin quantum dots with the long spin and valley coherence times.

cond-mat.mes-hall↗

arXiv2018

Spin Inertia of Resident and Photoexcited Carriers in Singly-Charged Quantum Dots

The spin dynamics in a broad range of systems can be studied using circularly polarized optical excitation with alternating helicity. The dependence of spin polarization on the frequency of helicity alternation, known as the spin inertia effect, is used here to study the spin dynamics in singly-charged (In,Ga)As/GaAs quantum dots (QDs) providing insight into spin generation and accumulation processes. We demonstrate that the dependence of spin polarization in $n$- and $p$-type QDs on the external magnetic field has a characteristic V- and M-like shape, respectively. This difference is related to different microscopic mechanisms of resident carriers spin orientation. It allows us to determine the parameters of the spin dynamics both for the ground and excited states of singly-charged QDs.

cond-mat.mes-hall↗

arXiv2018

Theory of spin inertia in singly-charged quantum dots

The spin inertia measurement is a recently emerged tool to study slow spin dynamics, which is based on the excitation of the system by a train of circularly polarized pulses with alternating helicity. Motivated by the experimental results reported in E. A. Zhukov et al., arXiv:1806.11100 we develop the general theory of spin inertia of localized charge carriers. We demonstrate that the spin inertia measurement in longitudinal magnetic field allows one to determine the parameters of the spin dynamics of resident charge carriers and of photoexcited trions, such as the spin relaxation times, longitudinal g-factors, parameters of hyperfine interaction and nuclear spin correlation times.

cond-mat.mes-hall↗

arXiv2018

Nonlinear light absorption in colloidal CdSe/CdS nanoplatelets

We investigated the nonlinear optical properties of CdSe/CdS nanoplatelets in the vicinity of heavy hole and light hole exciton resonances. The two color pump-probe technique was applied. The first intense pulse created non-equilibrium exciton population, which was detected as a decrease of probe light absorption. We observed intense scattering of excitons between heavy- and light-hole excitonic states. We also studied experimentally saturation of absorption in nanoplatelets. Theoretical description of these phenomena allowed us to determine parameters of exciton dynamics in nanoplatelets.

cond-mat.mes-hall↗

arXiv2018

Spin-related phenomena in two-dimensional hopping regime in magnetic field

The spin relaxation time of localized charge carriers is few orders of magnitude larger than that of free electrons and holes. Therefore mutual conversion of spin polarization, charge current and spin current turns out to be underlined in the hopping conductivity regime. We reveal different regimes of the coupled spin and charge dynamics depending on the relation between spin relaxation time and the characteristic hopping time. We derive kinetic equations to describe electrical spin orientation, dc spin-Hall effect, and spin galvanic effect in the transverse magnetic field. The generalized macroscopic conductivities describing these effects are calculated using percolation theory supported by numerical simulation. The conductivities change the sign at least once as functions of magnetic field for all values of the spin relaxation time.

cond-mat.mes-hall↗

arXiv2018

Spin and reoccupation noise in a single quantum dot beyond the fluctuation-dissipation theorem

We report on the nonequilibrium spin noise of a single InGaAs quantum dot charged by a single hole under strong driving by a linearly polarized probe light field. The spectral dependency of the spin noise power evidences a homogeneous broadening and negligible charge fluctuations in the environment of the unbiased quantum dot. Full analysis of the spin noise spectra beyond the fluctuation-dissipation theorem yields the heavy-hole spin dynamics as well as the trion spin dynamics. Moreover, the experiment reveals an additional much weaker noise contribution in the Kerr rotation noise spectra. This additional noise contribution has a maximum at the quantum dot resonance and shows a significantly longer correlation time. Magnetic-field-dependent measurements in combination with theoretical modeling prove that this additional noise contribution unveils a charge reoccupation noise which is intrinsic in naturally charged quantum dots.

cond-mat.mes-hall↗

arXiv2017

Homogenization of Doppler broadening in spin noise spectroscopy

The spin noise of cesium atoms vapor with admixture of buffer gas is experimentally investigated by measuring the spin induced Faraday rotation fluctuations in the vicinity of D 2 line. The line, under these conditions, is known to be strongly inhomogeneously broadened due to the Doppler effect. Despite that, optical spectrum of the spin noise power, as we have found, has the characteristic shape of the homogeneously broadened line with the dip at the line center. This fact is in stark contrast with the results of previous studies of inhomogeneous quantum dot ensembles. In addition, the two-color experiments, where correlations of the Faraday rotation fluctuations for two probe wavelengths were measured, have shown, in a highly spectacular way, that these fluctuations are either correlated, or anticorrelated depending on whether the two wavelengths lie on the same side, or on different sides of the resonance. The experimental data are explained within the developed theoretical model which takes into account both kinetics and spin dynamics of Cs atoms. It is shown that the unexpected behavior of the optical Faraday rotation noise spectra and effective homogenization of the optical transition in the spin-noise measurements are related to smallness of the momentum relaxation time of the atoms as compared with their spin relaxation time.

physics.atom-ph↗

arXiv2017

Measurement back-action and spin noise spectroscopy in a charged cavity-QED device in the strong coupling regime

We study theoretically the spin-induced and photon-induced fluctuations of optical signals from a singly-charged quantum dot-microcavity structure. We identify the respective contributions of the photon-polariton interactions, in the strong light-matter coupling regime, and of the quantum back-action induced by photon detection on the spin system. Strong spin projection by a single photon is shown to be achievable, allowing the initialization and measurement of a fully-polarized Larmor precession. The spectrum of second-order correlations is deduced, displaying information on both spin and quantum dot-cavity dynamics. The presented theory thus bridges the gap between the fields of spin noise spectroscopy and quantum optics.

cond-mat.mes-hall↗

arXiv2017

Nonequilibrium spin noise in a quantum dot ensemble

The spin noise in singly charged self-assembled quantum dots is studied theoretically and experimentally under the influence of a perturbation, provided by additional photoexcited charge carriers. The theoretical description takes into account generation and relaxation of charge carriers in the quantum dot system. The spin noise is measured under application of above barrier excitation for which the data are well reproduced by the developed model. Our analysis demonstrates a strong difference of the recharging dynamics for holes and electrons in quantum dots.

cond-mat.mes-hall↗

arXiv2016

Nuclear magnetic resonance and nuclear spin relaxation in AlAs quantum well probed by ESR

The study of nuclear magnetic resonance and nuclear spin-lattice relaxation was conducted in an asymmetrically doped to $n\sim1.8\times10^{11}$ cm$^{-2}$ 16 nm AlAs quantum well grown in the $[001]$-direction. Dynamic polarization of nuclear spins due to the hyperfine interaction resulted in the so-called Overhauser shift of the two-dimensional conduction electron spin resonance. The maximum shifts achieved in the experiments are several orders of magnitude smaller than in GaAs-based heterostructures indicating that hyperfine interaction is weak. The nuclear spin-lattice relaxation time extracted from the decay of Overhauser shift over time turned out to depend on the filling factor of the two-dimensional electron system. This observation indicates that nuclear spin-lattice relaxation is mostly due to the interaction between electron and nuclear spins. Overhauser shift diminishes resonantly when the RF-radiation of certain frequencies was applied to the sample. This effect served as an indirect, yet powerful method for nuclear magnetic resonance detection: NMR quadrupole splitting of $^{75}$As nuclei was clearly resolved. Theoretical calculations performed describe well these experimental findings.

cond-mat.mes-hall↗

arXiv2016

Stochastic Faraday rotation induced by the electric current fluctuations in nanosystems

We demonstrate theoretically that in gyrotropic semiconductors and semiconductor nanosystems the Brownian motion of electrons results in temporal fluctuations of the polarization plane of light passing through or reflected from the structure, i.e., in stochastic Faraday or Kerr rotation effects. The theory of the effects is developed for a number of prominent gyrotropic systems such as bulk tellurium, ensembles of chiral carbon nanotubes, and GaAs-based quantum wells of different crystallographic orientations. We show that the power spectrum of these fluctuations in thermal equilibrium is proportional to the ac conductivity of the system. We evaluate contributions resulting from the fluctuations of the electric current, as well as of spin, valley polarization, and the spin current to the noise of the Faraday/Kerr rotation. Hence, all-optical measurements of the Faraday and Kerr rotation noise provide an access to the transport properties of the semiconductor systems.

cond-mat.mes-hall↗

arXiv2016

Electrical spin orientation, spin-galvanic and spin-Hall effects in disordered two-dimensional systems

In disordered systems, the hopping conductivity regime is usually realized at low temperatures where spin-related phenomena differ strongly from the case of delocalized carriers. We develop the unified microscopic theory of current induced spin orientation, spin-galvanic and spin-Hall effects for the two-dimensional hopping regime. We show that the corresponding susceptibilities are proportional to each other and determined by the interplay between the drift and the diffusion spin currents. Estimations are made for realistic semiconductor heterostructures using the percolation theory. We show that the electrical spin polarization in the hopping regime increases exponentially with increase of the concentration of localization sites and may reach a few percents at the crossover from the hopping to the diffusion conductivity regime.

cond-mat.mes-hall↗

arXiv2016

Spin noise of electrons and holes in (In,Ga)As quantum dots: experiment and theory

The spin fluctuations of electron and hole doped self-assembled quantum dot ensembles are measured optically in the low-intensity limit of a probe laser in absence and presence of longitudinal or transverse static magnetic fields. The experimental results are modeled by two complementary approaches based either on semiclassical or quantum mechanical descriptions. This allows us to characterize the hyperfine interaction of electron and hole spins with the surrounding bath of nuclei on time scales covering several orders of magnitude. Our results demonstrate (i) the intrinsic precession of the electron spin fluctuations around the effective nuclear Overhauser field caused by the host lattice nuclear spins, (ii) the comparably long time scales for electron and hole spin decoherence, as well as (iii) the dramatic enhancement of the spin lifetimes induced by a longitudinal magnetic field due to the decoupling of nuclear and charge carrier spins.

cond-mat.mes-hall↗

arXiv2015

Theory of optical spin control in quantum dot microcavities

We present a microscopic theory of optical initialization, control and detection for a single electron spin in a quantum dot embedded into a zero-dimensional microcavity. The strong coupling regime of the trion and the cavity mode is addressed. We demonstrate that efficient spin orientation by a single circularly polarized pulse is possible in relatively weak transverse magnetic fields. The possibilities for spin control by additional circularly polarized pulse are analyzed. Under optimal conditions the Kerr and Faraday rotation angles induced by the spin polarized electron may reach tens of degrees.

cond-mat.mes-hall↗

arXiv2015

Spin-noise-based magnetometry of an $n$-doped GaAs microcavity in the field of elliptically polarized light

Recently reported optical nuclear orientation in the $n$-doped GaAs microcavity under pumping in nominal transparency region of the crystal [Appl. Phys. Lett. $\mathbf{106}$, 242405 (2015)] has arisen a number of questions, the main of them concerning mechanisms of angular momentum transfer from the light to the nuclear spin system and the nature of the light-related magnetic fields accompanying the optical nuclear polarization. In this paper, we use the spin noise spectroscopy for magnetometric purposes, particularly, to study effective fields acting upon electron spin system of an $n$-GaAs layer inside a high-Q microcavity in the presence of elliptically polarized probe beam. In addition to the external magnetic field applied to the sample in the Voigt geometry and the Overhauser field created by optically oriented nuclei, the spin noise spectrum reveals an additional effective, "optical," magnetic field produced by elliptically polarized probe itself. This field is directed along the light propagation axis, with its sign being determined by the sign of the probe helicity and its magnitude depending on degree of circular polarization and intensity of the probe beam. We analyze properties of this optical magnetic field and suggest that it results from the optical Stark effect in the field of the elliptically polarized electromagnetic wave.

cond-mat.mes-hall↗

arXiv2015

Spin dynamics and fluctuations in the streaming regime

Spin dynamics of two-dimensional electrons in moderate in-plane electric fields is studied theoretically. The streaming regime is considered, where each electron accelerates until reaching the optical phonon energy, then it emits an optical phonon, and a new period of acceleration starts. Spin-orbit interaction and elastic scattering result in anisotropic relaxation of electron spin polarization. The overall spin dynamics is described by a superposition of spin modes in the system. The relaxation time of the most long-living mode depends quasi-periodically on the inverse electric field. The spin modes can be conveniently revealed by means of spin noise spectroscopy. It is demonstrated that the spectrum of spin fluctuations consists of peaks with the low-frequency peak much narrower than satellite ones, and the widths of the peaks are determined by the decay times of the modes.

cond-mat.mes-hall↗

arXiv2014

Spin noise of localized electrons interacting with optically cooled nuclei

A microscopic theory of spin fluctuations of localized electrons interacting with optically cooled nuclear spin bath has been developed. Since nuclear spin temperature may stay low enough for macroscopically long time, the nuclear spin system becomes very sensitive to an external magnetic field. This strongly affects electron spin noise spectrum. It has been shown that in the case of weak fields/relatively high nuclear spin temperature, a small degree of nuclear spin polarization affect the electron spin fluctuations in the same way as an additional external magnetic field. By contrast, the high degree of nuclear polarization realized in relatively strong magnetic field and low nuclear spin temperature leads to a suppression of hyperfine field fluctuations and to a dramatic narrowing of precession-induced peak in the spin noise spectrum. The experimental possibilities of nuclear spin system investigation by means of spin noise spectroscopy are discussed.

cond-mat.mes-hall↗