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Yurii E. Lozovik

Publications and source records attributed to Yurii E. Lozovik.

71 records · Page 4Linked to original sources
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↗
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

Magnetoplasmons in layered graphene structures

We calculate the dispersion equations for magnetoplasmons in a single layer, a pair of parallel layers, a graphite bilayer and a superlattice of graphene layers in a perpendicular magnetic field. We demonstrate the feasibility of a drift-induced instability of magnetoplasmons. The magnetoplasmon instability in a superlattice is enhanced compared to a single graphene layer. The energies of the unstable magnetoplasmons could be in the terahertz (THz) part of the electromagnetic spectrum. The enhanced instability makes superlattice graphene a potential source of THz radiation.

cond-mat.mes-hall↗
arXiv2008

Theory of Bose-Einstein condensation and superfluidity of two-dimensional polaritons in an in-plane harmonic potential

Recent experiments have shown that it is possible to create an in-plane harmonic potential trap for a two-dimensional (2D) gas of exciton-polaritons in a microcavity structure, and evidence has been reported of Bose-Einstein condensation of polaritons accumulated in this type of trap. We present here the theory of Bose-Einstein condensation (BEC) and superfluidity of the exciton polaritons in a harmonic potential trap. Along the way, we determine a general method for defining the superfluid fraction in a 2D trap, in terms of angular momentum representation. We show that in the continuum limit, as the trap becomes shallower the superfluid fraction approaches the 2D Kosterlitz-Thouless limit, while the condensate fraction approaches zero, as expected.

cond-mat.mes-hall↗
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

Nanoelectromechanical systems based on multi-walled nanotubes: nanothermometer, nanorelay and nanoactuator

We report on three new types of nanoelectromechanical systems based on carbon nanotubes: an electromechanical nanothermometer, a nanorelay and a nanomotor. The nanothermometer can be used for accurate temperature measurements in spatially localized regions with dimensions of several hundred nanometers. The nanorelay is a prototype of a memory cell, and the nanoactuator can be used for transformation of the forward force into the relative rotation of the walls. Relative motion of the walls in these nanosystems is defined by the shape of the interwall interaction energy surface. Ab initio and semi-empirical calculations have been used to estimate the operational characteristics and dimensions of these nanosystems.

cond-mat.other↗
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↗
arXiv2007

Anomalous optical transmission through a vortex lattice in a film of type-II superconductor

We study the effect of anomalous optical transmission through an array of vortices in a type-II superconducting film subjected to a strong magnetic field. The mechanism responsible for this effect is resonance transmission between two surface plasmon polaritons (SPP) in the system. The SPP band gap in the system is studied as a function of magnetic field and temperature. Control of transmission by varying magnetic field and/or temperature is analyzed.

cond-mat.supr-con↗
arXiv2007

Bose-Einstein condensation and Superfluidity of magnetoexcitons in Graphene

We propose experiments to observe Bose-Einstein condensation (BEC) and superfluidity of quasi-two-dimensional (2D) spatially indirect magnetoexcitons in bilayer graphene. The magnetic field $B$ is assumed strong. The energy spectrum of collective excitations, the sound spectrum as well as the effective magnetic mass of magnetoexcitons are presented in the strong magnetic field regime. The superfluid density $n_S$ and the temperature of the Kosterlitz-Thouless phase transition $T_c$ are shown to be increasing functions of the excitonic density $n$ but decreasing functions of $B$ and the interlayer separation $D$. Numerical results are presented from these calculations.

cond-mat.str-el↗
arXiv2006

Superconducting photonic crystals

The band structure of a novel type of photonic crystal with superconducting constituent elements is calculated numerically via a plane wave expansion. The density of states and the dependence of the width of the photonic gap on the filling factor is analyzed for a two-dimensional photonic crystal consisting of an infinite array of parallel superconducting cylinders.

cond-mat.supr-con↗
arXiv2006

Superfluidity of "dirty" indirect excitons and magnetoexcitons in two-dimensional trap

The superfluid phase transition of bosons in a two-dimensional (2D) system with disorder and an external parabolic potential is studied. The theory is applied to experiments on indirect excitons in coupled quantum wells. The random field is allowed to be large compared to the dipole-dipole repulsion between excitons. The slope of the external parabolic trap is assumed to change slowly enough to apply the local density approximation (LDA) for the superfluid density, which allows us to calculate the Kosterlitz-Thouless temperature $T_{c}(n(r))$ at each local point $r$ of the trap. The superfluid phase occurs around the center of the trap ($\mathbf{r}=0$) with the normal phase outside this area. As temperature increases, the superfluid area shrinks and disappears at temperature $T_{c}(n(r=0))$. Disorder acts to deplete the condensate; the minimal total number of excitons for which superfluidity exists increases with disorder at fixed temperature. If the disorder is large enough, it can destroy the superfluid entirely. The effect of magnetic field is also calculated for the case of indirect excitons. In a strong magnetic field $H$, the superfluid component decreases, primarily due to the change of the exciton effective mass.

cond-mat.mes-hall↗
arXiv2005

Superfluidity of "dirty" indirect magnetoexcitons in coupled quantum wells in high magnetic field

Superfluidity in the quasi-two-dimensional (2D) system of spatially indirect magnetoexcitons in coupled quantum wells (CQW) and unbalanced two-layer electron system in high magnetic field $H$ is considered in the presence of a random field. The problem of the rare gas of magnetoexcitons with dipole-dipole repulsion in a random field has been reduced to the problem of the rare gas of dipole excitons without magnetic field with the effective magnetic mass of a magnetoexciton, which is a function of the magnetic field and parameters of the CQW, in an $H$-dependent effective random field. The density of the superfluid component $n_{s}$ and the temperature $T_{c}$ of the Kosterlitz-Thouless transition to a superfluid state are obtained as functions of magnetic field $H$, interlayer separation $D$ and the random field parameters $α_{i}$ and $g_{i}$. For 2D magnetoexcitonic systems, the rise of the magnetic field $H$ and the interwell distance $D$ is found to increase the effective renormalized random field parameter $Q$ and suppress the superfluid density $n_s$ and the temperature of the Kosterlitz-Thouless transition $T_c$. The suppressing influence of $D$ on $n_s$ and $T_c$ in strong magnetic filed is opposite to the case without magnetic field, when $n_s$ and $T_c$ increase with the rise of $D$ at fixed total exciton density $n$. It is shown that in the presence of the disorder at sufficiently large magnetic field $H$ or parameters of the disorder there is no superfluidity at any exciton density.

cond-mat.mes-hall↗
arXiv2004

Phase transitions in a system of indirect magnetoexcitons in coupled quantum wells at high magnetic field: the role of disorder

Collective properties of a quasi-two-dimensional (2D) system of spatially indirect magnetoexcitons in coupled quantum wells (CQW) in high magnetic field $H$ were analyzed in the presence of disorder. The Hamiltonian of the dilute gas of magnetoexcitons with dipole-dipole repulsion in a random field has been reduced to the Hamiltonian of a dilute gas of dipolar excitons without an applied magnetic field, but in an $H$-dependent effective random field and having an effective mass of magnetoexciton which is a function of the magnetic field and parameters of the CQW. For 2D magnetoexcitonic systems, the increase of the magnetic field $H$ and the interwell distance $D$ is found to increase the effective renormalized random field parameter $Q$ and suppress the superfluid density $n_s$ and the temperature of the Kosterlitz-Thouless transition $T_c$. It is shown that in the presence of the disorder there is a quantum transition to the superfluid state at zero temperature T=0 with respect to the magnetic field $H$ and the parameters of the disorder. There is no superfluidity at any exciton density in the presence of the disorder at sufficiently large magnetic field $H$ or sufficiently large disorder.

cond-mat.mes-hall↗
arXiv2004

Collective properties of indirect excitons in coupled quantum wells in random field

The influence of a random field induced by impurities, boundary irregularities etc. on the superfluidity of a quasi-two-dimensional (2D) system of spatially indirect excitons in coupled quantum wells is studied. The interaction between excitons is taken into account in the ladder approximation. The random field is allowed to be large compared to the dipole-dipole repulsion between excitons. The coherent potential approximation (CPA) allows us to derive the exciton Green's function for a wide range of the random field, and the CPA results are used in the weak-scattering limit, which results in the second-order Born approximation. The Green's function of the collective excitations for the cases of (1) equal electron and hole masses and (2) the ``heavy hole'' limit are derived analytically. For quasi-two-dimensional excitonic systems, the density of the superfluid component and the Kosterlitz-Thouless temperature of the superfluid phase transition are obtained, and are found to decrease as the random field increases. This puts constraints on the experimental efforts to observe excitonic superfluidity.

cond-mat.mes-hall↗
arXiv2004

Superfluidity of "dirty" indirect excitons in coupled quantum wells

The theory of what happens to a superfluid in a random field, known as the ``dirty boson'' problem, directly relates to a real experimental system presently under study by several groups, namely excitons in coupled semiconductor quantum wells. We consider the case of bosons in two dimensions in a random field, when the random field can be large compared to the repulsive exciton-exciton interaction energy, but is small compared to the exciton binding energy. The interaction between excitons is taken into account in the ladder approximation. The coherent potential approximation allows us to derive the exciton Green's function for a wide range of the random field strength, and in the weak-scattering limit CPA results in the second-order Born approximation. For quasi-two-dimensional excitonic systems, the density of the superfluid component and the Kosterlitz-Thouless temperature of the superfluid phase transition are obtained, and are found to decrease as the random field increases.

cond-mat.mes-hall↗
arXiv2003

Nanomachines Based on Carbon Nanotubes

The possibility for double-wall carbon nanotube to operate as the bolt and nut pair is studied. The barriers for relative motions of walls along the helical "thread" line and for jumps on neighbour helical lines are calculated as functions of wall lengths for the set of double-wall carbon nanotubes. The dynamics of relative motion of carbon nanotube walls along the helical line under the action of external forces is considered. Perforated nanodrill, variable nanoresistor and other principally new nanotube based mechanical nanodevices using these motion are proposed. Possible operation modes of proposed nanodevices are discussed.

cond-mat.mes-hall↗
arXiv2001

Orientational melting of two-shell carbon nanoparticles: molecular dynamics study

The energetic characteristics of two-shell carbon nanoparticles ("onions") with different shapes of second shell are calculated. The barriers of relative rotation of shells are found to be surprisingly small; therefore, free relative rotation of shells can take place at room temperature. The intershell orientational melting of the nanoparticle $C_{60}@C_{240}$ is studied by molecular dynamics. The parameters of Arrhenius formula for jump rotational intershell diffusion are calculated. The definition of orientational melting temperature is proposed as the temperature when the transition probability over barrier between equivalent potential minima is equal to 1/2. The temperature of orientational melting of the nanoparticle $C_{60}@C_{240}$ is about 60 K.

physics.atm-clus↗