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Roman Ya. Kezerashvili

Publications and source records attributed to Roman Ya. Kezerashvili.

At least 91 records · Page 5Linked to original sources
arXiv2010

The Poynting-Robertson Effect on Solar Sails

We consider a special relativistic effect, known as the Poynting-Robertson effect, on various types of trajectories of solar sails. Since this effect occurs at order $v^ϕ/c$, where $v^ϕ$ is the tangential speed relative to the sun, it can dominate over other special relativistic effects, which occur at order $v^2/c^2$. While solar radiation can be used to propel the solar sail, the absorbed portion of it also gives rise to a drag force in the tangential direction. For escape trajectories, this diminishes the cruising velocity, which can have a cumulative effect on the heliocentric distance. For a solar sail directly facing the sun in a bound orbit, the Poynting-Robertson effect decreases its orbital speed, thereby causing it to slowly spiral towards the sun. We also consider this effect for non-Keplerian orbits in which the solar sail is tilted in the azimuthal direction. While in principle the drag force could be counter-balanced by an extremely small tilt of the solar sail in the polar direction, periodic adjustments are more feasible.

physics.space-ph↗
arXiv2010

Drag effects in the system of electrons and microcavity polaritons

The theory of the drag effects in the system of spatially separated electrons and excitons in coupled quantum wells (QW) embedded in an optical microcavity is developed. It is shown that at low temperature an electron current induces the (normal component) polariton flow, therefore, a transport of photons along the cavity. However, the electron current dragged by the polariton flow is strongly suppressed below polariton superfluid transition temperature and hence, the strong suppression of the induced electron current indicates the superfluidity of polaritons. Therefore, the transport properties of polaritons can be investigated by measuring the current or voltage in the electron subsystem. At high temperatures we study the exciton-electron drag effects. At high temperatures regime, from one hand, the existence of the electric current in an electron QW induces the exciton flow in the other QW, from the other hand, the electron current in one QW induces the exciton flow in the other QW via the drag of excitons by the electrons. The drag coefficients for the polariton-electron systems are calculated and analyzed. We discuss the possible experimental observation of the drag effects in the system of electrons and microcavity polaritons, that also allow to observe the cavity polaritons superfluidity.

cond-mat.mes-hall↗
arXiv2010

Can we move photons?

The drag effects in the system of spatially separated electrons and excitons in coupled quantum wells (CQWs) embedded in an optical microcavity are predicted. It is shown that at low temperature an electron current induces the polariton flow, therefore, a transport of photons along the cavity. However, the superfluid polariton component does not contribute to the electron drag. The polariton-electron at the low temperatures and exciton-electron at the high temperatures drag coefficients are presented. It is shown that the drag coefficients increase when temperature increases. We discuss possible experiments for the observation of the electron-polariton drag effect.

cond-mat.mes-hall↗
arXiv2010

Excitation of Meinel and first negative band system at the collision of electron and proton with nitrogen molecule

Absolute cross sections for the $e-$N$_{2}$ and $p-$N$_{2}$ collisions for the first negative B$^{2}Σ_{u}^{+}-$X$^{2}Σ_{g}^{+}$ and Meinel A% $^{2}Π_{u}-$X$^{2}Σ_{g}^{+}$ bands have been measured in the energy region of 400-1500 eV for electrons and 0.4-10 keV for protons, respectively. Measurements are performed in the visible spectral region of 400-800 nm by an optical spectroscopy method. The ratio of the cross sections of the Meinel band system to the cross section of the first negative band system (0,0) does not depend on the incident electron energy. The population of vibrational levels corresponding to A$^{2}Π_{u}$ states are consistent with Franck-Condon principle. The ratio of the cross sections of (4,1) to (3,0) bands, and (5,2) to (3,0) bands exhibits slight dependence on the proton energy. The theoretical estimation within the quasimolecular approximation provides a reasonable description of the total cross section for the first negative band.

physics.atom-ph↗
arXiv2009

Bose-Einstein condensation of quasiparticles in graphene

The collective properties of different quasiparticles in various graphene based structures in high magnetic field have been studied. We predict Bose-Einstein condensation (BEC) and superfluidity of 2D spatially indirect magnetoexcitons in two-layer graphene. The superfluid density and the temperature of the Kosterlitz-Thouless phase transition are shown to be increasing functions of the excitonic density but decreasing functions of magnetic field and the interlayer separation. The instability of the ground state of the interacting 2D indirect magnetoexcitons in a slab of superlattice with alternating electron and hole graphene layers (GLs) is established. The stable system of indirect 2D magnetobiexcitons, consisting of pair of indirect excitons with opposite dipole moments, is considered in graphene superlattice. The superfluid density and the temperature of the Kosterlitz-Thouless phase transition for magnetobiexcitons in graphene superlattice are obtained. Besides, the BEC of excitonic polaritons in GL embedded in a semiconductor microcavity in high magnetic field is predicted. While superfluid phase in this magnetoexciton polariton system is absent due to vanishing of magnetoexciton-magnetoexciton interaction in a single layer in the limit of high magnetic field, the critical temperature of BEC formation is calculated. The essential property of magnetoexcitonic systems based on graphene (in contrast, e.g., to a quantum well) is stronger influence of magnetic field and weaker influence of disorder. Observation of the BEC and superfluidity of 2D quasiparticles in graphene in high magnetic field would be interesting confirmation of the phenomena we have described.

cond-mat.mes-hall↗
arXiv2009

Bose-Einstein condensation of trapped polaritons in 2D electron-hole systems in a high magnetic field

The Bose-Einstein condensation (BEC) of magnetoexcitonic polaritons in two-dimensional (2D) electron-hole system embedded in a semiconductor microcavity in a high magnetic field $B$ is predicted. There are two physical realizations of 2D electron-hole system under consideration: a graphene layer and quantum well (QW). A 2D gas of magnetoexcitonic polaritons is considered in a planar harmonic potential trap. Two possible physical realizations of this trapping potential are assumed: inhomogeneous local stress or harmonic electric field potential applied to excitons and a parabolic shape of the semiconductor cavity causing the trapping of microcavity photons. The effective Hamiltonian of the ideal gas of cavity polaritons in a QW and graphene in a high magnetic field and the BEC temperature as functions of magnetic field are obtained. It is shown that the effective polariton mass $M_{\rm eff}$ increases with magnetic field as $B^{1/2}$. The BEC critical temperature $T_{c}^{(0)}$ decreases as $B^{-1/4}$ and increases with the spring constant of the parabolic trap. The Rabi splitting related to the creation of a magnetoexciton in a high magnetic field in graphene and QW is obtained. It is shown that Rabi splitting in graphene can be controlled by the external magnetic field since it is proportional to $B^{-1/4}$, while in a QW the Rabi splitting does not depend on the magnetic field when it is strong.

cond-mat.mes-hall↗
arXiv2009

Bose-Einstein condensation of polaritons in graphene in a high magnetic field

The Bose-Einstein condensation (BEC) of magnetoexcitonic polaritons in a graphene layer embedded in a optical microcavity in a high magnetic field $B$ is predicted. The essential property of this system (in contrast, e.g., to a quantum well embedded in a cavity) is stronger influence of magnetic field and weaker influence of disorder. A two-dimensional (2D) magnetoexcitonic polaritons gas is considered in a planar harmonic electric field potential applied to excitons or a parabolic shape of the optical cavity causing the trapping of microcavity photons. It is shown that the effective polariton mass $M_{\rm eff}$ increases with magnetic field as $B^{1/2}$. The BEC critical temperature $T_{c}^{(0)}$ decreases as $B^{-1/4}$ and increases with the spring constant of the parabolic trap. The Rabi splitting related to the creation of a magnetoexciton in a high magnetic field in graphene is obtained.

cond-mat.mes-hall↗
arXiv2009

Deviations from Keplerian Orbits for Solar Sails

It is shown that the curvature of spacetime, a possible net electric charge on the sun, a small positive cosmological constant and the oblateness of the sun, in conjunction with solar radiation pressure (SPR), affect the bound orbital motion of solar sails and lead to deviations from Kepler's third law for heliocentric and non-Keplerian orbits. With regards to the Lense-Thirring effect, the SRP increases the amount of precession per orbit for polar orbits. Non-Keplerian polar orbits exhibit an analog of the Lense-Thirring effect in which the orbital plane precesses around the sun.

gr-qc↗
arXiv2009

Escape Trajectories of Solar Sails and General Relativity

General relativity can have a significant impact on the long-range escape trajectories of solar sails deployed near the sun. Spacetime curvature in the vicinity of the sun can cause a solar sail traveling from 0.01 AU to 2550 AU to be deflected by as much as one million kilometers, and should therefore be taken into account at the beginning of the mission. There are a number of smaller general relativistic effects, such as frame dragging due to the slow rotation of the sun which can cause a deflection of more than one thousand kilometers.

gr-qc↗
arXiv2009

Solar Radiation Pressure and Deviations from Keplerian Orbits

Newtonian gravity and general relativity give exactly the same expression for the period of an object in circular orbit around a static central mass. However, when the effects of the curvature of spacetime and solar radiation pressure are considered simultaneously for a solar sail propelled satellite, there is a deviation from Kepler's third law. It is shown that solar radiation pressure affects the period of this satellite in two ways: by effectively decreasing the solar mass, thereby increasing the period, and by enhancing the effects of other phenomena, rendering some of them detectable. In particular, we consider deviations from Keplerian orbits due to spacetime curvature, frame dragging from the rotation of the sun, the oblateness of the sun, a possible net electric charge of the sun, and a very small positive cosmological constant.

gr-qc↗
arXiv2009

Influence of high-angle grain boundaries on the charge order formation in the $\mathrm{YBa_2Cu_3O_{7-δ}}$

We are examining the possibility of the formation of charge order in the high-temperature superconductor $\mathrm{YBa_2Cu_3O_{7-δ}}$ (YBCO) due to interaction between the charged oxygen vacancies or di-vacancies. The molecular dynamics method is used to analyze the displacement fields around these defects. The distribution of displacements around a single charged oxygen vacancy and di-vacancy, determination of binding energy of oxygen vacancy in di-vacancy demonstrate that there is, in principle, the possibility of the charge order formation in YBCO by charged oxygen vacancies or di-vacancies. It is shown that the charge order formation first of all should be formed near crystal lattice defects and that the high-angle grain boundaries (GBs) regions are preferable places for this formation. The adsorption capability of high-angle GBs with respect to the stripe embryo formation is determined. It is shown that there is a proportional dependence between the repetition distance along the high-angle GBs and an energy advantage of the stripe embryo formation in GBs.

cond-mat.supr-con↗
arXiv2009

Bound Orbits of Solar Sails and General Relativity

We study how the curvature of spacetime, in conjunction with solar radiation pressure (SRP), affects the bound orbital motion of solar sails. While neither the curvature of spacetime nor the SRP alter the form of Kepler's third law by themselves, their simultaneous effects lead to deviations from this law. We also study deviations from Keplerian motion due to frame dragging, the gravitational multipole moments of the sun, a possible net electric charge on the sun, and a positive cosmological constant. The presence of the SRP tends to increase these deviations by several orders of magnitude, possibly rendering some of them detectable. As for non-circular bound orbits, the SRP dampens the rate at which the perihelion is shifted due to curved spacetime, while the perihelion shift due to the oblateness of the sun is increased. With regards to the Lense-Thirring effect, the SRP increases the angle of precession of polar orbits during one orbital period, although the precession frequency is not actually altered. We also consider non-Keplerian orbits, which lie outside of the plane of the sun. In particular, we investigate how the pitch angle of the solar sail is affected by the partial absorption of light by the sail, general relativistic effects, and the oblateness of the sun. Non-Keplerian orbits exhibit an analog of the Lense-Thirring effect, in that the orbital plane precesses around the sun. A near-solar mission for observations of these effects could provide an interesting confirmation of these phenomena.

gr-qc↗
arXiv2008

Microscopic Approach to Analyze Solar-Sail Space-Environment Effects

Near-sun space-environment effects on metallic thin films solar sails as well as hollow-body sails with inflation fill gas are considered. Analysis of interaction of the solar radiation with the solar sail materials is presented. This analysis evaluates worst-case solar radiation effects during solar-radiation-pressure acceleration. The dependence of the thickness of solar sail on temperature and on wavelength of the electromagnetic spectrum of solar radiation is investigated. Physical processes of the interaction of photons, electrons, protons and helium nuclei with sail material atoms and nuclei, and inflation fill gas molecules are analyzed. Calculations utilized conservative assumptions with the highest values for the available cross sections for interactions of solar photons, electrons and protons with atoms, nuclei and hydrogen molecules. It is shown that for high-energy photons, electrons and protons the beryllium sail is mostly transparent. Sail material will be partially ionized by solar UV and low-energy solar electrons. For a hollow-body photon sail effects including hydrogen diffusion through the solar sail walls, and electrostatic pressure is considered. Electrostatic pressure caused by the electrically charged sail's electric field may require mitigation since sail material tensile strength decreases with elevated temperature.

physics.space-ph↗
arXiv2008

Anomalous far infrared monochromatic transmission through a film of type-II superconductor in magnetic field

Anomalous far infrared monochromatic transmission through a lattice of Abrikosov vortices in a type-II superconducting film is found and reported. The transmitted frequency corresponds to the photonic mode localized by the defects of the Abrokosov lattice. These defects are formed by extra vortices placed out of the nodes of the ideal Abrokosov lattice. The extra vortices can be pinned by crystal lattice defects of a superconductor. The corresponding frequency is studied as a function of magnetic field and temperature in the framework of the Dirac-type two-band model. While our approach is valid for all type-II superconductors, the specific calculations have been performed for the YBa$_{2}$Cu$_{3}$O$_{7-δ}$ (YBCO). The control of the transmitted frequency by varying magnetic field and/or temperature is analyzed. It is suggested that found anomalously transmitted localized mode can be utilized in the far infrared monochromatic filters.

cond-mat.supr-con↗
arXiv2008

The beryllium hollow-body solar sail: exploration of the Sun's gravitational focus and the inner Oort Cloud

Spacecraft kinematics, peak perihelion temperature and space environment effects during solar-radiation-pressure acceleration for a beryllium hollow-body interstellar solar sail inflated with hydrogen fill gas are investigated. We demonstrate that diffusion is alleviated by an on-board fill gas reserve and electrostatic pressure can be alleviated by increasing perihelion distance. For a 0.1 AU perihelion, a 937 m radius sail with a sail mass of 150 kg and a payload mass of 150 kg, perihelion sail temperature is about 1000 K, peak acceleration is about 0.6 g, and solar-system exit velocity is about 400 km/s. After sail deployments, the craft reaches the 200 AU heliopause in 2.5 years, the Sun's inner gravitational focus at 550 AU in about 6.5 years and 2,550 AU in 30 years. The Be hollow-body sail could be applied in the post 2040 time frame to verify general relativity predictions regarding the Sun's inner gravitational focus and to explore particles and fields in the Sun's inner Oort Comet Cloud.

physics.space-ph↗
arXiv2008

Support of Study on Engineering Technology from Physics and Mathematics

An approach that provides students with an ability to transfer learning in physics and mathematics to the engineering-technology courses through e-teaching and e-learning process is proposed. E-modules of courses in mathematics, physics, computer systems technology, and electrical and telecommunications engineering technology have been developed. These modules being used in the Blackboard and Web-based communications systems create a virtual interdisciplinary learning community, which helps the students to transfer knowledge from physics and mathematics to their study in engineering technology.

physics.ed-ph↗
arXiv2008

Collective properties of magnetobiexcitons in quantum wells' and graphene superlattices

We propose the Bose-Einstein condensation (BEC) and superfluidity of quasi-two-dimensional (2D) spatially indirect magnetobiexcitons in a slab of superlattice with alternating electron and hole layers consisting from the semiconducting quantum wells (QWs) and graphene superlattice in high magnetic field. The two different Hamiltonians of a dilute gas of magnetoexcitons with a dipole-dipole repulsion in superlattices consisting of both QWs and graphene layers in the limit of high magnetic field have been reduced to one effective Hamiltonian a dilute gas of two-dimensional excitons without magnetic field. Moreover, for $N$ excitons we have reduced the problem of $2N\times 2$ dimensional space onto the problem of $N\times 2$ dimensional space by integrating over the coordinates of the relative motion of an electron (e) and a hole (h). The instability of the ground state of the system of interacting two-dimensional indirect magnetoexcitons in a slab of superlattice with alternating electron and hole layers in high magnetic field is established. The stable system of indirect quasi-two-dimensional magnetobiexcitons, consisting of pair of indirect excitons with opposite dipole moments is considered. The density of superfluid component $n_{s}(T)$ and the temperature of the Kosterlitz-Thouless phase transition to the superfluid state in the system of two-dimensional indirect magnetobiexcitons, interacting as electrical quadrupoles, are obtained for both QW and graphene realizations.

cond-mat.mes-hall↗
arXiv2007

Bose-Einstein condensation and superfluidity of magnetobiexcitons in quantum wells' and graphene superlattices

We propose the Bose-Einstein condensation (BEC) and superfluidity of quasi-two-dimensional (2D) spatially indirect magnetobiexcitons in a slab of superlattice with alternating electron and hole layers consisting from the semiconducting quantum wells (QWs) and graphene superlattice in high magnetic field. The two different Hamiltonians of a dilute gas of magnetoexcitons with a dipole-dipole repulsion in superlattices consisting of both QWs and graphene layers in the limit of high magnetic field have been reduced to one effective Hamiltonian a dilute gas of two-dimensional excitons without magnetic field. Moreover, for $N$ excitons we have reduced the problem of $2N\times 2$ dimensional space onto the problem of $N\times 2$ dimensional space by integrating over the coordinates of the relative motion of an electron (e) and a hole (h). The instability of the ground state of the system of interacting two-dimensional indirect magnetoexcitons in a slab of superlattice with alternating electron and hole layers in high magnetic field is established. The stable system of indirect quasi-two-dimensional magnetobiexcitons, consisting of pair of indirect excitons with opposite dipole moments is considered. The density of superfluid component $n_{s}(T)$ and the temperature of the Kosterlitz-Thouless phase transition to the superfluid state in the system of two-dimensional indirect magnetobiexcitons, interacting as electrical quadrupoles, are obtained for both QW and graphene realizations.

cond-mat.mes-hall↗