arXiv subjects

Roman Ya. Kezerashvili

Publications and source records attributed to Roman Ya. Kezerashvili.

At least 37 records · Page 2Linked to original sources

arXiv2022

On superfluidity of indirect excitons in transition metals trichalcogenides van der Waals heterostructures

We predict angle-dependent superfluidity for a new class of 2D materials -- transition metals trichalcogenides (TMTC). Within a mean-field approach superfluidity of indirect excitons in TMTC van der Waals heterostructures (vdWHs) is studied. We use different potentials for charged carriers interaction to analyze the influence of the screening on the studied phenomena. Our study demonstrates the angle-dependent superfluidity temperature in TMTC vdWHs: for a given density a maximum and minimum $T_c$ of superfluidity occurs along chain and $a$-directions, respectively. This work can guide experimental research toward the realization of anisotropic superfluidity in TMTC vdWH. We suggest an experiment for the observation of anisotropic superfluidity in TMTC vdWH.

cond-mat.mes-hall↗

arXiv2022

Solar sail with inflatable toroidal shell

In the framework of a strict mathematical approach based on classical theory of elasticity we present an idea of the deployment and stretching of the circular solar sail attached to the inflatable toroidal shell. It is predicted that by introducing the gas into the inflatable toroidal shell one can deploy and stretch a large size circular solar sail membrane. The formulas for the toroidal shell and sail membrane stresses and strains caused by the gas pressure in the shell are derived. The analytical expressions can be applied to a wide range of solar sail sizes. Numerical calculations for the sail of radii up to 100 m made of CP1 membrane and attached to the toroidal shell with the varied cross-section radius are presented. The normal transverse vibration modes of the sail membrane under tension caused by gas pressure in the shell are calculated. The feasibility of deployment and stretching of a solar sail with a large size circular membrane attached to the inflatable toroidal shell is demonstrated.

physics.space-ph↗

arXiv2022

Charge-dipole and dipole-dipole interactions in two-dimensional materials

We derive the explicit analytical form for the charge-dipole and dipole-dipole interactions in 2D configuration space. We demonstrate that the reduction of dimensionality can alter the charge-dipole and dipole-dipole interactions in 2D case. The asymptotics of these interactions at large distances coincide to the charge-dipole and dipole-dipole interactions in 3D configuration space.

cond-mat.mes-hall↗

arXiv2021

Magnetoexcitons in phosphorene monolayers, bilayers, and van der Waals heterostructures

We study direct and indirect excitons in Rydberg states in phosphorene monolayers, bilayer and van der Waals (vdW) heterostructure in an external magnetic field, applied perpendicular to the monolayer or heterostructure within the framework of the effective mass approximation. Binding energies of magnetoexcitons are calculated by a numerical integration of the Schrodinger equation using the Rytova-Keldysh potential for direct magnetoexcitons and both the Rytova-Keldysh and Coulomb potentials for indirect one. The latter allows to understand the role of screening in phosphorene. We report the magnetic field energy contribution to the binding energies and diamagnetic coefficients (DMCs) for magnetoexcitons that strongly depend on the effective mass of electron and hole and their anisotropy and can be tuned by the external magnetic field. We demonstrate theoretically that the vdW phosphorene heterostructure is a novel category of 2D semiconductor offering a tunability of the binding energies of magnetoexcitons by mean of external magnetic field and control the binding energies and DMCs by the number of hBN layers separated two phosphorene sheets. Such tunability is potentially useful for the devices design.

cond-mat.mes-hall↗

arXiv2021

Exploration of the solar system and beyond using a thermonuclear fusion drive

It is demonstrated that the development of a nuclear fusion rocket engine based on a D $-$ $^{3}$He (Deterium-Helium 3) technology will allow to travel in the solar system and beyond. The Direct Fusion Drive (DFD) is the D $-$ $^{3}$He-fueled, aneutronic, thermonuclear fusion propulsion system that is under development at Princeton University Plasma Physics Laboratory [1]. It is considered and analyzed the Earth-Mars mission using the DFD. It is shown that one-way trips to Mars in slightly more than 100 days become possible and also journeys to the asteroid belt will take about 250 days [2]. It is presented an analysis of realistic new trajectories for a robotic mission to Saturn's largest moon, Titan, to demonstrate the great advantages related to the thermonuclear DFD. The trajectories calculations and analysis for Saturn's largest moon Titan different profile missions are given based on the characteristics of a 2 MW class DFD engine. This capability results in a total trip duration of 2.6 years for the thrust-coast-thrust profile and less than 2 years for the continuous thrust profile [3]. Using the same 2 MW class DFD engine one can reach some trans-Neptunian object, such as the dwarf planets Makemake, Eris, and Haumea in less than 10 years with a payload mass of at least 1500 kg, so that it would enable all kind of missions, from scientific observation to in-situ operations [4]. We consider for each mission a Thrust-Coast-Thrust profile. For this reason, each mission is divided into 3 phases: i. the trajectory to escape Earth gravity influence; ii. the interplanetary travel, from the exit of Earth sphere of influence to the end of the coasting phase; iii. maneuvers to rendezvous with a target object. We present calculations to reach a vicinity at 125 AU.

physics.pop-ph↗

arXiv2021

Solar sail with superconducting circular current-carrying wire

Background: A solar sail presents a large sheet of low areal density membrane and is the most elegant propellant-less propulsion system for the future exploration of the Solar System and beyond. By today the study on sail membrane deployment strategies has attracted considerable attention. Goal: In this work we present an idea of the deployment and stretching of the circular solar sail. We consider the superconducting current loop attached to the thin membrane %to develop a new (method) approach of deployment of a solar sail and and predict that a superconducting current loop can deploy and stretch the circular solar sail membrane. Method: In the framework of a strict mathematical approach based on the classical electrodynamics and theory of elasticity the magnetic field induced by the superconducting current loop and elastic properties of a circular solar sail membrane and wire loop are analyzed. The formulas for the wire and sail membrane stresses and strains caused by the current in the superconducting wire are derived. Results: The obtained analytical expressions can be applied to a wide range of solar sail sizes. Numerical calculations for the sail of radius of 5 m to 150 m made of CP1 membrane of the thickness of 3.5 $μm$ attached to Bi$-$2212 superconducting wire with the cross-section radius of 0.5 mm to 10 mm are presented. Calculations are performed for the engineering current densities of 100 A/mm$^{2}$ to 1000 A/mm$^{2}$. Conclusion: Our calculations demonstrate the feasibility of the proposed idea for the solar sail deployment for the future exploration of the deep space by means of the light pressure propellant.

physics.pop-ph↗

arXiv2021

Magnetoexcitons in transition-metal dichalcogenides monolayers, bilayers, and van der Waals heterostructures

We study direct and indirect magnetoexcitons in Rydberg states in monolayers and heterostructures of transition-metal dichalcogenices (TMDCs) in an external magnetic field, applied perpendicular to the monolayer or heterostructures. We calculate binding energies of magnetoexcitons for the Rydberg states 1$s$, 2$s$, 3$s$, and 4$s$ by numerical integration of the Schrödinger equation using the Rytova-Keldysh potential for direct magnetoexcitons and both the Rytova-Keldysh and Coulomb potentials for indirect magnetoexcitons. Latter allows understanding the role of screening in TMDCs heterostructures. We report the magnetic field energy contribution to the binding energies and diamagnetic coefficients (DMCs) for direct and indirect magnetoexcitons. The tunability of the energy contribution of direct and indirect magnetoexcitons by the magnetic field is demonstrated. It is shown that binding energies and DMCs of indirect magnetoexcitons can be manipulated by the number of hBN layers. Therefore, our study raises the possibility of controlling the binding energies of direct and indirect magnetostrictions in TMDC monolayers, bilayers and heterostructures using magnetic field and opens an additional degree of freedom to tailor the binding energies and DMCs for heterostructures by varying the number of hBN sheets between TMDC layers. The calculations of the binding energies and DMCs of indirect magnetoexcitons in TMDC heterostructures are novel and can be compared with the experimental results when they will be available.

cond-mat.mes-hall↗

arXiv2021

Effects of parallel electric and magnetic fields on Rydberg excitons in buckled two-dimensional materials

We study direct and indirect magnetoexcitons in Rydberg states in monolayers and double-layer heterostructures of Xenes (silicene, germanene, and stanene) in external parallel electric and magnetic fields, applied perpendicular to the monolayer and heterostructure. We calculate binding energies of magnetoexcitons for the Rydberg states 1$s$, 2$s$, 3$s$, and 4$s$, by numerical integration of the Schrödinger equation using the Rytova-Keldysh potential for direct magnetoexciton and both the Rytova-Keldysh and Coulomb potentials for indirect excitons. Latter allows understanding a role of screening in Xenes. In the external perpendicular electric field, the buckled structure of the Xene monolayers leads to appearance of potential difference between sublattices allowing to tune electron and hole masses and, therefore, the binding energies and diamagnetic coefficients (DMCs) of magnetoexcitons. We report the energy contribution from electric and magnetic fields to the binding energies and DMCs. The tunability of the energy contribution of direct and indirect magnetoexcitons by electric and magnetic fields is demonstrated. It is also shown that DMCs of direct excitons can be tuned by the electric field, and the DMCs of indirect magnetoexcitons can be tuned by the electric field and manipulated by the number of h-BN layers. Therefore, these allowing the possibility of electronic devices design that can be controlled by external electric and magnetic fields and the number of h-BN layers. The calculations of the binding energies and DMCs of magnetoexcitons in Xenes monolayers and heterostructures are novel and can be compared with the experimental results when they will be available.

cond-mat.mes-hall↗

arXiv2021

Crystal Phases of Charged Interlayer Excitons in van der Waals Heterostructures

Throughout the years, strongly correlated coherent states of excitons have been the subject of intense theoretical and experimental studies. This topic has recently boomed due to new emerging quantum materials such as van der Waals (vdW) bound atomically thin layers of transition metal dichalcogenides (TMDs). We analyze the collective properties of charged interlayer excitons observed recently in bilayer TMD heterostructures. We predict new strongly correlated phases - crystal and Wigner crystal - that can be selectively realized with TMD bilayers of properly chosen electron-hole effective masses by just varying their interlayer separation distance. Our results open up new avenues for nonlinear coherent control, charge transport and spinoptronics applications with quantum vdW heterostuctures.

cond-mat.mes-hall↗

arXiv2020

Strain induced quantum Hall effect of excitons in graphene

We study the effect of a uniform pseudomagnetic field, induced by a strain in a monolayer and double layer of gapped graphene, acting on excitons. For our analysis it is crucial that the pseudomagnetic field acts on the charges of the constituent particles of the excitons, i.e., the electrons and holes, the same way in contrast to a magnetic field. Moreover, using a circularly polarized laser field, the electrons and the holes can be excited only in one valley of the honeycomb lattice of gapped graphene. This breaks the time-reversal symmetry and provides the possibility to observe the various Quantum Hall phenomena in this pseudomagnetoexciton system. Our study poses a fundamental problem of the quantum Hall effect for composite particles and paves the way for quantum Hall physics of pseudomagnetoexcitons.

cond-mat.mes-hall↗

arXiv2020

Exploration of trans-Neptunian objects using the Direct Fusion Drive

The Direct Fusion Drive (DFD) is a nuclear fusion engine that will provide thrust and electrical power for any spacecraft. It is a compact engine, based on the D -$^{3}$He aneutronic fusion reaction that uses the Princeton field reversed configuration for the plasma confinement and an odd parity rotating magnetic field as heating method to achieve nuclear fusion (Cohen et al., 2019), which will heat the deuterium, also used as propellant. \par In this work we present possibilities to explore the solar system outer border using the DFD. The objective is to reach some trans-Neptunian object, such as the dwarf planets Makemake, Eris and Haumea in less than 10 years with a payload mass of at least of 1500 kg, so that it would enable all kind of missions, from scientific observation to in-situ operations. For each mission a thrust-coast-thrust profile is considered. For this reason, each mission is divided into 3 phases: i. the spiral trajectory to escape Earth gravity; ii. the interplanetary travel, from the exit of Earth sphere of influence to the end of the coasting phase; iii. maneuvers to rendezvous with the dwarf planet. Propellant mass consumption, initial and final masses, velocities and $ΔV$ for each maneuver are presented. Calculations to reach a vicinity at 125 AU for the study of Sun magnetosphere as well as Eris via flyby are also presented, with interest on the influence of different acceleration phases. Our calculations show that a spacecraft propelled by DFD will open unprecedented possibilities to explore the border of the solar system, in a limited amount of time and with a very high payload to propellant masses ratio.

physics.space-ph↗

arXiv2020

A Titan mission using the Direct Fusion Drive

The main purpose of this work is to perform an analysis of realistic new trajectories for a robotic mission to Saturn's largest moon, Titan, in order to demonstrate the great advantages related to the Direct Fusion Drive (DFD). The DFD is a D -$^3$He fuelled, aneutronic, thermonuclear fusion propulsion system. This fusion propulsion concept is based on a magnetically confined field reversed configuration plasma, where the deuterium propellant is heated by fusion products, and then expanded into a magnetic nozzle, providing both thrust and electrical energy to the spacecraft [1]. The trajectories calculations and analysis for the Titan mission are obtained based on the characteristics provided by the PPPL [1]. Two different profile missions are considered: the first one is a thrust-coast-thrust profile with constant thrust and specific impulse; the second scenario is a continuous and constant thrust profile mission. Each mission study is divided into four different phases, starting from the initial low Earth orbit departure, the interplanetary trajectory, Saturn orbit insertion and the Titan orbit insertion. For all mission phases, maneuver time and propellant consumption are calculated. The results of calculations and mission analysis offer a complete overview of the advantages in term of payload mass and travel time. It is important to emphasize that the deceleration capability is one of the DFD game changer: in fact, the DFD performance allows to rapidly reach high velocities and decelerate in even shorter time period. This capability results in a total trip duration of 2.6 years for the thrust-coast-thrust profile and less than 2 years considering the continuous thrust profile. The high payload enabling capability, combined with the huge electrical power available from the fusion reactor, leads to a tremendous advantage compared to present technology.

physics.space-ph↗

arXiv2020

Chiral filtration of light by Weyl-semimetal medium

Recently discussed topological materials Weyl-semimetals (WSs) combine both: high electron mobility comparable with graphene and unique topological protection of Dirac points. We present novel results related to electromagnetic field propagation through WSs. It is predicted that transmission of the normally incident polarized electromagnetic wave (EMW) through the WS strongly depends on the orientation of polarization with respect to a gyration vector $\mathbf{g}$. The latter is related to the vector-parameter $\mathbf{b}$, which represents the separation between the Weyl nodes of opposite chirality in the first Brillouin zone. By changing the polarization of the incident EMW with respect to the gyration vector $\mathbf{g}$ the system undergoes the transition from the isotropic dielectric to the medium with Kerr- or Faraday-like rotation of polarization and finally to the system with chiral selective electromagnetic field. It is shown that WSs can be applied as the polarization filters.

cond-mat.mes-hall↗

arXiv2020

Achieving the required mobility in the solar system through Direct Fusion Drive

To develop a spacefaring civilization, humankind must develop technologies which enable safe, affordable and repeatable mobility through the solar system. One such technology is nuclear fusion propulsion which is at present under study mostly as a breakthrough toward the first interstellar probes. The aim of the present paper is to show that fusion drive is even more important in human planetary exploration and constitutes the natural solution to the problem of exploring and colonizing the solar system.

physics.pop-ph↗

arXiv2019

Dynamics of a qubit-oscillator system with periodically varying coupling

The dynamics of qubits coupled to a harmonic oscillator with time-periodic coupling is investigated in the framework of Floquet theory. This system can be used to model nonadiabatic phenomena that require a periodic modulation of the qubit/oscillator coupling. The case of a single qubit coupled to a resonator populated with $n= 0,1$ photons is explicitly treated. The time-dependent Schrödinger equation describing the system's dynamics is solved within the Floquet formalism and a perturbative approach in the time- and Laplace-domain. Good quantitative agreement is found between the analytical and numerical calculations within the Floquet approach, making it the most promising candidate for the study of time-periodic problems. Nonetheless, the time- or Laplace-domain perturbative approaches can be used in the presence of aperiodic time-dependent terms in the Hamiltonian.

quant-ph↗

arXiv2019

Inflation deployed torus-shaped solar sail accelerated via thermal desorption of coating

A torus-shaped sail consists of a reflective membrane attached to an inflatable torus-shaped rim. The sail's deployment from its stowed configuration is initiated by introducing inflation pressure into the toroidal rim with an attached circular flat membrane coated by heat-sensitive materials that undergo thermal desorption (TD) from a solid to a gas phase. Our study of the deployment and acceleration of the sail is split into three steps: at a particular heliocentric distance a torus-shaped sail is deployed by a gas inflated into the toroidal rim and the membrane is kept flat by the pressure of the gas; under heating by solar radiation, the membrane coat undergoes TD and the sail is accelerated via TD of coating and solar radiation pressure (SRP); when TD ends, the sail utilizes thrust only from SRP. We study the stability of the torus-shaped sail and deflection and vibration of the flat membrane due to the acceleration by TD and SRP. The stability of the toroidal rim is addressed.

physics.space-ph↗

arXiv2019

Optical Properties of Anisotropic Excitons in Phosphorene

We study the eigenenergies and optical properties of both direct excitons in a phosphorene monolayer in different dielectric environments, and indirect excitons in heterostructures of phosphorene with hexagonal boron nitride. For these systems, we solve the 2D Schrödinger equation using the Rytova-Keldysh (RK) potential for direct, and both the RK and Coulomb potentials for indirect excitons. The results show that excitons formed from charge carriers with anisotropic effective mass exhibit enhanced (suppressed) optical absorption, compared to their 2D isotropic counterparts, under linearly polarized excitations along the crystal axis with relatively smaller (larger) effective carrier masses. This anisotropy leads to dramatically different excited states than the isotropic exciton. The direct exciton binding energy depends strongly on the dielectric environment, and shows good agreement with previously published data. For indirect excitons, the oscillator strength and absorption coefficient increase as the interlayer separation increases. The choice of RK or Coulomb potential does not significantly change the indirect exciton optical properties, but leads to significant differences in the binding energy for small interlayer separation.

cond-mat.mes-hall↗

arXiv2019

Few-body systems in condensed matter physics

This review focuses on the studies and computations of few-body systems of electrons and holes in condensed matter physics. We analyze and illustrate the application of a variety of methods for description of two- three- and four-body excitonic complexes such as an exciton, trion and biexciton in three-, two- and one-dimensional configuration spaces in various types of materials. We discuss and analyze the contributions made over the years to understanding how the reduction of dimensionality affects the binding energy of excitons, trions and biexcitons in bulk and low dimensional semiconductors and address the challenges that still remain.

cond-mat.mes-hall↗