arXiv subjects

V. K. Kalevich

Publications and source records attributed to V. K. Kalevich.

At least 19 recordsLinked to original sources

arXiv2025

Kerr effect induced by exchange interaction of electrons separated by a tunnel barrier in a double quantum well

In a structure with two tunnel-coupled quantum wells of different widths, the spin dynamics resulting from resonant pulsed optical pumping of the narrow-well exciton includes the wide-well electron magnetization dynamics. Our analysis shows that the effect is driven by electron exchange between narrow-well excitons and spin-polarized electrons in the wide well. A theoretical model of the spin Kerr effect has been developed accounting for the interwell electron spin exchange. In the studied double-well structure with CdTe and Cd$_{0.98}$Mn$_{0.02}$Te quantum wells and a well-separating barrier thickness of 5 monolayers (1.6 nm), the model accurately describes the experimental results and allows us to estimate the interwell electron exchange constant as $δ_{e} \approx 0.9\times10^{-15}~\textrm{eV}~\textrm{cm}^{2}$.

cond-mat.mes-hall↗

arXiv2023

Local field of spin-spin interactions in the nuclear spin system of n-GaAs

At low lattice temperatures the nuclear spins in a solid form a closed thermodynamic system that is well isolated from the lattice. Thermodynamic properties of the nuclear spin system are characterized by the local field of spin-spin interactions, which determines its heat capacity and the minimal achievable nuclear spin temperature in demagnetization experiments. We report the results of measurement of the local field for the nuclear spin system in GaAs, which is a model material for semiconductor spintronics. The choice of the structure, a weakly doped GaAs epitaxial layer with weak residual deformations, and of the measurement method, the adiabatic demagnetization of optically cooled nuclear spins, allowed us to refine the value of nuclear spin-spin local field, which turned out to be two times less than one previously obtained. Our experimental results are supported by calculations, which take into account dipole-dipole and indirect (pseudodipolar and exchange) nuclear spin interactions as well as quadrupole splitting of nuclear spins in the vicinity of charged impurity centers.

cond-mat.mtrl-sci↗

arXiv2021

Warm-up spectroscopy of quadrupole-split nuclear spins in n-GaAs epitaxial layers

The efficiency of the adiabatic demagnetization of nuclear spin system (NSS) of a solid is limited, if quadrupole effects are present. Nevertheless, despite a considerable quadrupole interaction, recent experiments validated the thermodynamic description of the NSS in GaAs. This suggests that nuclear spin temperature can be used as the universal indicator of the NSS state in presence of external perturbations. We implement this idea by analyzing the modification of the NSS temperature in response to an oscillating magnetic field at various frequencies, an approach termed as the warm-up spectroscopy. It is tested in a n-GaAs sample where both mechanical strain and built-in electric field may contribute to the quadrupole splitting, yielding the parameters of electric field gradient tensors for 75As and both Ga isotopes, 69Ga and 71Ga.

cond-mat.mes-hall↗

arXiv2021

Chiral photodetector based on GaAsN

The detection of light helicity is key to several research and industrial applications from drugs production to optical communications. However, the direct measurement of the light helicity is inherently impossible with conventional photodetectors based on III-V or IV-VI semiconductors, being naturally non-chiral. The prior polarization analysis of the light by a series of often moving optical elements is necessary before light is sent to the detector. A method is here presented to effectively give to the conventional dilute nitride GaAs-based semiconductor epilayer a chiral photoconductivity in paramagnetic-defect-engineered samples. The detection scheme relies on the giant spin-dependent recombination of conduction electrons and the accompanying spin polarization of the engineered defects to control the conduction band population via the electrons' spin polarization. As the conduction electron spin polarization is, in turn, intimately linked to the excitation light polarization, the light polarization state can be determined by a simple conductivity measurement. This effectively gives the GaAsN epilayer a chiral photoconductivity capable of discriminating the handedness of an incident excitation light in addition to its intensity. This approach, removing the need of any optical elements in front of a non-chiral detector, could offer easier integration and miniaturisation. This new chiral photodetector could potentially operate in a spectral range from the visible to the infra-red using (In)(Al)GaAsN alloys or ion-implanted nitrogen-free III-V compounds.

physics.app-ph↗

arXiv2021

Polarization sensitive photodectector based on GaAsN

We propose and numerically simulate an optoelectronic compact circular polarimeter. It allows to electrically measure the degree of circular polarization and light intensity at room temperature for a wide range of incidence angles in a single shot. The device, being based on GaAsN, is easy to integrate into standard electronics and does not require bulky movable parts nor extra detectors. Its operation hinges mainly on two phenomena: the spin dependent capture of electrons and the hyperfine interaction between bound electrons and nuclei on Ga$^{2+}$ paramagnetic centers in GaAsN. The first phenomenon confers the device with sensitivity to the degree of circular polarization and the latter allows to discriminate the handedness of the incident light.

cond-mat.mes-hall↗

arXiv2020

Superfluid currents in half-moon polariton condensates

We excite exciton-polariton condensates in half-moon shapes by the non-resonant optical excitation of GaAs-based cylindrical pillar microcavities. In this geometry, the π-jump of the phase of the condensate wave function coexists with a gradual {\pm π} phase variation between two horns of the half-moon. We switch between clockwise and counter-clockwise phase currents by slightly shifting the excitation spot on the surface of the pillar. Half-moon condensates are expected to reveal features of two-level quantum systems similar to superconducting flux qubits

cond-mat.mes-hall↗

arXiv2019

Electron-nucleus spin correlation conservation of the spin dependent recombination in Ga$^{2+}$ centers

Spin dependent recombination in GaAsN offers many interesting possibilities in the design of spintronic devices mostly due to its astounding capability to reach conduction band electron spin polarizations close to 100% at room temperature. The mechanism behind the spin selective capture of electrons in Ga$^{2+}$ paramagnetic centers is revisited in this paper to address inconsistencies common to most previously presented models. Primarily, these errors manifest themselves as major disagreements with the experimental observations of two key characteristics of this phenomenon: the effective Overhauser-like magnetic field and the width of the photoluminescence Lorentzian-like curves as a function of the illumination power. These features are not only essential to understand the spin dependent recombination in GaAsN, but are also key to the design of novel spintronic devices. Here we demonstrate that the particular structure of the electron capture expressions introduces spurious electron-nucleus correlations that artificially alter the balance between the hyperfine and the Zeeman contributions. This imbalance strongly distorts the effective magnetic field and width characteristics. In this work we propose an alternative recombination mechanism that preserves the electron-nucleus correlations and, at the same time, keeps the essential properties of the spin selective capture of electrons. This mechanism yields a significant improvement to the agreement between experimental and theoretical results. In particular, our model gives results in very good accord with the experimental effective Overhauser-like magnetic field and width data, and with the degree of circular polarization under oblique magnetic fields.

cond-mat.mes-hall↗

arXiv2017

Persistent circular currents of exciton-polaritons in cylindrical pillar microcavities

We have experimentally observed an eddy current of exciton polaritons arising in a cylindrical GaAs/AlGaAs pillar microcavity under the nonresonant optical pumping. The polariton current manifests itself in a Mach-Zehnder interferometry image as a characteristic spiral that occurs due to the interference of the light emitted by an exciton-polariton condensate with a spherical wave artificially shaped from the emission of the same condensate. We have experimentally observed the condensates with the topological charges m = +1, m = -1 and m = -2. The interference pattern corresponding to the m = -2 current represents the twin spiral emerging from the center of the micropillar.

cond-mat.mes-hall↗

arXiv2017

Electron-nuclear coherent spin oscillations probed by spin dependent recombination

We demonstrate the detection of coherent electron-nuclear spin oscillations related to the hyperfine interaction and revealed by the band-to-band photoluminescence (PL) in zero external magnetic field. On the base of a pump-probe PL experiment we measure, directly in the temporal domain, the hyperfine constant of an electron coupled to a gallium defect in GaAsN by tracing the dynamical behavior of the conduction electron spin-dependent recombination to the defect site. The hyperfine constants and the relative abundance of the nuclei isotopes involved can be determined without the need of electron spin resonance technique and in the absence of any magnetic field. Information on the nuclear and electron spin relaxation damping parameters can also be estimated from the oscillations damping and the long delay behavior.

cond-mat.mes-hall↗

arXiv2016

Electron-nuclear spin dynamics of Ga$^{2+}$ paramagnetic centers probed by spin dependent recombination: A master equation approach

Similar to nitrogen-vacancy centers in diamond and impurity atoms in silicon, interstitial gallium deep paramagnetic centers in GaAsN have been proven to have useful characteristics for the development of spintronic devices. Among other interesting properties, under circularly polarized light, gallium centers in GaAsN act as spin filters that dynamically polarize free and bound electrons reaching record spin polarizations (100\%). Furthermore, the recent observation of the amplification of the spin filtering effect under a Faraday configuration magnetic field has suggested that the hyperfine interaction that couples bound electrons and nuclei permits the optical manipulation of its nuclear spin polarization. Even though the mechanisms behind the nuclear spin polarization in gallium centers are fairly well understood, the origin of nuclear spin relaxation and the formation of an Overhauser-like magnetic field remain elusive. In this work we develop a model based on the master equation approach to describe the evolution of electronic and nuclear spin polarizations of gallium centers interacting with free electrons and holes. Our results are in good agreement with existing experimental observations. In regard to the nuclear spin relaxation, the roles of nuclear dipolar and quadrupolar interactions are discussed. Our findings show that, besides the hyperfine interaction, the spin relaxation mechanisms are key to understand the amplification of the spin filtering effect and the appearance of the Overhauser-like magnetic field. Based on our model's results we propose an experimental protocol based on time resolved spectroscopy. It consists of a pump-probe photoluminescence scheme that would allow the detection and the tracing of the electron-nucleus flip-flops through time resolved PL measurements.

cond-mat.other↗

arXiv2016

Spin-dependent recombination in GaAs(1-x)N(x) alloys at oblique magnetic field

We have studied experimentally and theoretically the optical orientation and spin-dependent Shockley-Read-Hall recombination in a semiconductor in a magnetic field at an arbitrary angle between the field and circularly polarized exciting beam. The experiments are performed at room temperature in GaAsN alloys where deep paramagnetic centers are responsible for the spin-dependent recombination. The observed magnetic-field dependences of the circular polarization r(B) and intensity J(B) of photoluminescence can be approximately described as a superposition of two Lorentzian contours, normal and inverted, with their half-widths differing by an order of magnitude. The normal (narrow) Lorentzian contour is associated with depolarization of the transverse (to the field) component of spin polarization of the localized electrons, whereas the inverted (broad) Lorentzian is due to suppression of the hyperfine interaction of the localized electron with the defect nucleus. The ratio between the height of one Lorentzian and depth of the other is governed by the field tilt angle. In contrast to the hyperfine interaction of a shallow-donor-bound electron with a large number of nuclei of the crystal lattice, in the optical orientation of the electron-nuclear system under study no additional narrow peak appears in the oblique field. This result demonstrates that in the GaAsN alloys the hyperfine interaction of the localized electron with the single nucleus of the paramagnetic center remains strong even at room temperature. For a theoretical description of the experiment, we have extended the theory of spin-dependent recombination via deep paramagnetic centers with the nuclear angular momentum I = 1/2 developed previously for the particular case of the longitudinal field. The calculated curves r(B), J(B) agree with the approximate description of the experimental dependences as a sum of two Lorentzians.

cond-mat.mes-hall↗

arXiv2014

Spin-dependent recombination and hyperfine interaction at the deep defects

We present a theoretical study of optical electron-spin orientation and spin-dependent Shockley-Read-Hall recombination taking into account the hyperfine coupling between the bound-electron spin and the nuclear spin of a deep paramagnetic center. We show that the number of master rate equations for the components of the electron-nuclear spin-density matrix is considerably reduced due to the restrictions imposed by the axial symmetry of the system under consideration. The rate equations describe the Zeeman splitting of the electron spin sublevels in the longitudinal magnetic field, the spin relaxation of free and bound electrons, and the nuclear spin relaxation in the two defect states, with one and two (singlet) bound electrons. The general theory is developed for an arbitrary value of the nuclear spin I, the magnetic-field and excitation-power dependencies of the electron and nuclear spin polarizations are calculated for the particular value of I = 1/2. The role of the nuclear spin relaxation in each of the both defect states is analyzed. The circular polarization and intensity of the edge photoluminescence as well as the dynamic nuclear spin polarization as functions of the excitation power are shown to have bell-shaped forms

cond-mat.mes-hall↗

arXiv2014

Controllable structuring of exciton-polariton condensates in cylindrical pillar microcavities

We observe condensation of exciton polaritons in quantum states composed of concentric rings when exciting cylindrical pillar GaAs/AlGaAs microcavities non-resonantly by a focused laser beam normally incident at the center of the pillar. The number of rings depends on the pumping intensity and the pillar size, and may achieve 5 in the pillar of 40 mkm diameter. Breaking the axial symmetry when moving the excitation spot away from the pillar center leads to transformation of the rings into a number of bright lobes corresponding to quantum states with nonzero angular momenta. The number of lobes, their shape and location are dependent on the spot position. We describe the out-of-equilibrium condensation of polaritons in the states with different principal quantum numbers and angular momenta with a formalism based on Boltzmann-Gross-Pitaevskii equations accounting for repulsion of polaritons from the exciton reservoir formed at the excitation spot and their spatial confinement by the pillar boundary.

cond-mat.mes-hall↗

arXiv2013

Ring-shaped polariton lasing in pillar microcavities

Optically generated exciton-polaritons in cylindric semiconductor pillar microcavity with embedded GaAs/AlGaAs quantum wells demonstrate a clear polariton lasing regime. When exciting in the center of the pillar we detect a ring-shaped emission, where the peak of intensity can be separated from the excitation spot by more than 10 micrometers. The spatial coherence of the ring emission is verified by interferometry measurements. These observations are interpreted by drift of the exciton polariton condensate away from the excitation spot due to its repulsion from the exciton reservoir and by its spatial confinement by the pillar boundary.

cond-mat.mes-hall↗

arXiv2012

Optical orientation of nuclei in nitrogen alloys GaAsN at room temperature

The intensity and the giant circular polarization of edge luminescence in a longitudinal magnetic field have been measured in nitrogen alloys GaAsN under circularly polarized pumping. It has been found that these dependences are shifted with respect to zero field by a value Beff. The magnitude of the internal field Beff increases with increase in pumping intensity and reaches saturation (~250 Gauss) at great densities of excitation. The saturation of the Beff field with growth of pumping indicates that this is a field of nuclei, polarized dynamically due to hyperfine interaction with optically oriented deep paramagnetic centers, rather than a field of exchange interaction created on the center by spin-polarized photo-excited conduction electrons. The short time of nuclear polarization by electrons (<15 mks), measured under modulation of circular polarization of the exciting light with high frequency, points to a small number of nuclei undergoing hyperfine interaction with an electron localized at a center.

cond-mat.mes-hall↗

arXiv2011

Amplification of spin-filtering effect by magnetic field in GaAsN alloys

We have found that intensity $I$ and circular polarization degree $ρ$ of the edge photoluminescence, excited in GaAsN alloys by circularly polarized light at room temperature, grow substantially in the longitudinal magnetic field $B$ of the order of 1\,kG. This increase depends on the intensity of pumping and, in the region of weak or moderate intensities, may reach a twofold value. In two-charge-state model, which considers spin-dependent recombination of spin-oriented free electrons on deep paramagnetic centers, we included the magnetic-field suppression of spin relaxation of the electrons bound on centers. The model describes qualitatively the rise of $ρ$ and $I$ in a magnetic field under different pump intensities. Experimental dependences $ρ(B)$ and $I(B)$ are shifted with respect to zero of the magnetic field by a value of $\sim$170\,Gauss, while the direction of the shift reverses with change of the sign of circular polarization of pumping. As a possible cause of the discovered shift we consider the Overhauser field, arising due to the hyperfine interaction of an electron bound on a center with nuclei of the crystal lattice in the vicinity of the center.

cond-mat.mes-hall↗

arXiv2010

Optical orientation and spin-dependent recombination in GaAsN alloys under continuous-wave pumping

We present a systematic theoretical study of spin-dependent recombination and its effect on optical orientation of photoelectron spins in semiconductors with deep paramagnetic centers. For this aim we generalize the Shockley-Read theory of recombination of electrons and holes through the deep centers with allowance for optically-induced spin polarization of free and bound electrons. Starting from consideration of defects with three charge states we turn to the two-charge-state model possessing nine parameters and show that it is compatible with available experimental data on undoped GaAsN alloys. In the weak- and strong-pumping limits, we derive simple analytic equations which are useful in prediction and interpretation of experimental results. Experimental and theoretical dependencies of the spin-dependent-recombination ratio and degree of photoluminescence circular polarization on the pumping intensity and the transverse magnetic field are compared and discussed.

cond-mat.mes-hall↗

arXiv2008

The sign of electron g-factor in GaAs(1-x)N(x) measured by using the Hanle effect

Positive signs of the effective g-factors for free electrons in the conduction band and electrons localized on deep paramagnetic centers have been measured in nitrogen dilute alloy GaAs{0.979}N{0.021} at room temperature. The g-factor signs have been determined from an asymmetry in the depolarization of edge photoluminescence in a transverse magnetic field (Hanle effect) at the oblique incidence of the exciting radiation and oblique-angle detection of the luminescence. The tilted spin polarization of free electrons is induced under interband absorption of circularly polarized light, and the paramagnetic centers acquire spin polarization because of spin-dependent capture of free spin-polarized electrons by these centers. The measured Hanle curve is a superposition of two lines, narrow and broad, with the widths ~400 G and ~50000 G, arising due to the depolarization of localized and free electrons, respectively. The magnitude and direction of the asymmetry in the measured Hanle curve have been found to depend on the partial contributions to the photoluminecsence from the heavy- and light-hole subbands split by a uniaxial deformation of the GaAs{1-x}N{x} film grown on a GaAs substrate. We have extended the theory of optical orientation in order to calculate the excitation spectrum of the photoelectron tilted-spin polarization and the circularly-polarized luminescence spectrum taking into account that, in the strained samples under study, the light-hole subband lies above the heavy-hole one. The results have further been used to calculate the shape of Hanle curve as a function of the excitation and registration energies as well as the incidence and detection angles and to compare the theory with experiment.

cond-mat.mes-hall↗