Roman Ya. Kezerashvili

Graphene-based one-dimensional photonic crystal

A novel type of one-dimensional (1D) photonic crystal formed by an array of periodically located stacks of alternating graphene and dielectric stripes embedded into a background dielectric medium is proposed. The wave equation for the electromagnetic wave propagating in such a structure is solved in the framework of the Kronig-Penney model. The frequency band structure of the 1D graphene-based photonic crystal is obtained analytically as a function of the filling factor and the thickness of the dielectric between the graphene stripes. The photonic frequency corresponding to the electromagnetic wave localized by a defect of the photonic crystal formed by an extra dielectric placed in the position of one stack of alternating graphene and dielectric stripes is obtained.

Graphene-based photonic crystal

A novel type of photonic crystal formed by embedding a periodic array of constituent stacks of alternating graphene and dielectric discs into a background dielectric medium is proposed. The photonic band structure and transmittance of such photonic crystal are calculated. The graphene-based photonic crystals can be used effectively as the frequency filters and waveguides for the far infrared region of electromagnetic spectrum. Due to substantial suppression of absorption of low-frequency radiation in doped graphene the damping and skin effect in the photonic crystal are also suppressed. The advantages of the graphene-based photonic crystal are discussed.

Superfluidity of dipole excitons in the presence of band gaps in two-layer graphene

A study of the formation of excitons as a problem of two Dirac particles confined in two-layer graphene sheets separated by a dielectric when gaps are opened and they interact via a Coulomb potential is presented. We propose to observe Bose-Einstein condensation and superfluidity of quasi-two-dimensional dipole excitons in double layer graphene in the presence of band gaps. The energy spectrum of the collective excitations, the sound spectrum, and the effective exciton mass are functions of the energy gaps, density and interlayer separation. The superfluid density ns and temperature of the Kosterlitz-Thouless phase transition Tc are decreasing functions of the energy gaps as well as the interlayer separation, and therefore, could be controlled by these parameters.

Graphene nanoribbon based spaser

A novel type of spaser with the net amplification of surface plasmons (SPs) in a doped graphene nanoribbon is proposed. The plasmons in the THz region can be generated in a doped graphene nanoribbon due to nonradiative excitation by emitters like two level quantum dots located along a graphene nanoribbon. The minimal population inversion per unit area, needed for the net amplification of SPs in a doped graphene nanoribbon, is obtained. The dependence of the minimal population inversion on the surface plasmon wave vector, graphene nanoribbon width, doping, and damping parameters necessary for the amplification of surface plasmons in the armchair graphene nanoribbon is studied.

Bound orbits of solar sails and general relativity

Abstract We study general relativistic effects on the bound orbits of solar sails. The combined effects of spacetime curvature and solar radiation pressure (SRP) lead to deviations from Kepler’s third law. Such kind of deviations also arise from frame dragging, the gravitational multipole moments of the sun, a net electric charge on the sun, and a positive cosmological constant. The SRP increases these deviations by several orders of magnitude, possibly rendering some of them detectable. We consider how the SRP modifies the perihelion shift of non-circular orbits, as well as the Lense-Thirring effect involving the precession of polar orbits. We investigate how the pitch angle for non-Keplerian orbits changes due to the partial absorption of light, general relativistic effects, and the oblateness of the sun. It is predicted that there is an analog of the Lense-Thirring effect for non-Keplerian orbits, in that the orbital plane precesses around the sun. We also consider the Poynting–Robertson effect and show that this effect can, in principle, be compensated for by an extremely small tilt of the solar sail.

High-temperature superfluidity of the two-component Bose gas in a transition metal dichalcogenide bilayer

The high-temperature superfluidity of two-dimensional dipolar excitons in two parallel TMDC layers is predicted. We study Bose-Einstein condensation in the two-component system of dipolar A and B excitons. The effective mass, energy spectrum of the collective excitations, the sound velocity and critical temperature are obtained for different TMDC materials. It is shown that in the Bogolubov approximation the sound velocity in the two-component dilute exciton Bose gas is always larger than in any one-component. The difference between the sound velocities for two-component and one-component dilute gases is caused by the fact that the sound velocity for two-component system depends on the reduced mass of A and B excitons, which is always smaller than the individual mass of A or B exciton. Due to this fact, the critical temperature Tc for superfluidity for the two-component exciton system in TMDC bilayer is about one order of magnitude higher than Tc in any one-component exciton system. We propose to observe the superfluidity of two-dimensional dipolar excitons in two parallel TMDC layers, which causes two opposite superconducting currents in each TMDC layer.

Collective properties of magnetobiexcitons in quantum wells' and graphene superlattices

The Bose-Einstein condensation and superfluidity of quasi-two-dimensional 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 are considered. The two different Hamiltonians of a dilute gas of magnetoexcitons with a dipole-dipole repulsion in superlattices, consisting of both QWs and graphene layers (GLs) in the limit of high magnetic field, have been reduced to one effective Hamiltonian\char22{}a dilute gas of two-dimensional excitons with the renormalized effective mass of the magnetoexciton, which depends on the magnetic field. This Hamiltonian does not include the vector potential. Moreover, for

Solar radiation pressure and deviations from Keplerian orbits

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Coupling of two Dirac particles

excitons we have reduced the problem of

Superfluidity of dipolar excitons in a transition metal dichalcogenide double layer

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