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P. V. Ratnikov

Publications and source records attributed to P. V. Ratnikov.

16 recordsLinked to original sources
arXiv2023

Dielectric electron-hole liquid in monolayer heterostructures based on transition metal dichalcogenides

The possibility of the appearance of a dielectric electron-hole liquid (EHL) in monolayers of transition metal dichalcogenides and heterostructures based on them is considered. It is shown that the coherent pairing of electrons and holes in them leads to the formation of a dielectric EHL when the degree of circular polarization of the exciting light exceeds a certain threshold value. Below this value, a metallic EHL is realized. Some possible physical manifestations of the transition between these two types of EHL are noted.

cond-mat.mes-hall↗
arXiv2022

Trion gas, electron-hole liquid, and metal-insulator transition in doped heterostructures based on transition metal dichalcogenides

The effect of doping on the parameters of an electron-hole liquid (EHL) in heterostructures based on transition metal dichalcogenides is studied. The phase diagram of the EHL is constructed. It is shown that for the formation of a high-temperature tightly bound EHL, as well as for the transition from the semiconducting (exciton) state to the semimetallic one (electron-hole plasma/liquid), it is advantageous to dope the energy band with larger number of valleys. The transition from trion gas to electron-hole plasma is investigated using the modified Mott criterion and variational calculation with screened potential. The effect of doping on the metal--insulator transition in the equilibrium case without laser excitation is studied.

cond-mat.mes-hall↗
arXiv2021

Phase diagram of electron-hole liquid in monolayer heterostructures based on transition metal dichalcogenides

In the last few years, interest in monomolecular layers of transition metal dichalcogenides (TMDs) has been driven by their unusual electronic and optical properties, which are very attractive for designing functional elements of new generation nanoelectronics. Recently, experimental evidence has appeared for the formation of a high-temperature strongly bound electron-hole liquid (EHL) in TMD monolayers. Strong binding of charge carriers is due to a significant decrease in the screening of the Coulomb interaction in monolayer heterostructures. In this work, the gas--liquid phase transition in a system of electrons and holes in quasi-two-dimensional heterostructures based on TMDs is considered and the critical parameters of such a transition are calculated. The metal-insulator transition is described and the phase diagram for such heterostructures is constructed.

cond-mat.mes-hall↗
arXiv2020

Electron-Hole Liquid in Monolayer Transition Metal Dichalcogenide Heterostructures

Monolayer films of transition metal dichalcogenides (in particular, MoS2, MoSe2, WS2, and WSe2) can be considered as ideal systems for the studies of high-temperature electron-hole liquids. The quasi-two-dimensional nature of electrons and holes ensures their stronger interaction as compared to that in bulk semiconductors. The screening of the Coulomb interaction in monolayer heterostructures is significantly reduced, since it is determined by the permittivities of the environment (e.g., vacuum and substrate), which are much lower than those characteristic of the films of transition metal dichalcogenides. The multivalley structure of the energy spectrum of charge carriers in transition metal dichalcogenides significantly reduces the kinetic energy, resulting in the increase in the equilibrium density and binding energy of the electron-hole liquid. The binding energy of the electron-hole liquid and its equilibrium density are determined. It is shown that the two-dimensional Coulomb potential should be used in the calculations for the electron-hole liquid.

cond-mat.mes-hall↗
arXiv2016

On the Dispersion Relation of Magnetoplasmons in a Planar Graphene-Based Superlattice

The dispersion relation for magnetoplasmons in a planar superlattice with periodically alternating regions of gapless and gapped modications of graphene has been derived within the frame of the random-phase approximation. The contribution of virtual transitions between the lower electron miniband and the upper hole miniband to the polarization operator has been taken into account in addition to the contribution of virtual intra-miniband transitions.

cond-mat.mes-hall↗
arXiv2016

Plasmons in a Planar Graphene Superlattice

Plasmon collective excitations are studied in a planar graphene superlattice formed by periodically alternating regions of gapless graphene and of its gapped modification. The plasmon dispersion law is determined both for the quasi-one-dimensional case (the Fermi level is located within the minigap) and for the quasi-two-dimensional case (the Fermi level is located within the miniband). The problem concerning the absorption of modulated electromagnetic radiation at the excitation of plasmons is also considered.

cond-mat.mes-hall↗
arXiv2014

Novel Type of Superlattices Based on Gapless Graphene with the Alternating Fermi Velocity

We study a novel type of graphene-based superlattices formed owing to a periodic modulation of the Fermi surface. Such a modulation is possible for graphene deposited on a striped substrate made of materials with substantially different values of the dc permittivity. Similar superlattices appear also in graphene sheets applied over substrates with a periodic array of parallel grooves. We suggest a model describing such superlattices. Using the transfer-matrix technique, we determine the dispersion relation and calculate the energy spectrum of these superlattices. We also analyze at a qualitative level the current--voltage characteristics of the system under study.

cond-mat.mes-hall↗
arXiv2013

Effects of quantum zero-point spin fluctuations on the ground state of plutonium

The magnetic stability of δ-plutonium is analyzed taking into account zero-point spin fluctuations. Within the generalized theory of spin fluctuations described within a simple phenomenological model neglecting its spatial dispersion we show that zero-point local magnetic moments are giant (at.Pu) and suppress the magnetic order predicted by ab initio calculations resulting in the observed paramagnetic state of δ-plutonium.

cond-mat.str-el↗
arXiv2012

Superlattice Based on Graphene on a Strip Substrate

A graphene-based superlattice formed due to the periodic modulation of the band gap has been investigated. Such a modulation is possible in graphene deposited on a strip substrate made of silicon oxide and hexagonal boron nitride. The advantages and some possible problems in the superlattice under consideration are discussed. A model describing such a superlattice is proposed and the dispersion relation between the energy and momentum of carriers has been obtained using the transfer matrix method within this model.

cond-mat.mes-hall↗
arXiv2012

Size Quantization in Planar Graphene-Based Heterostructures: Pseudospin Splitting, Interface States, and Excitons

A planar quantum-well device made of a gapless graphene nanoribbon with edges in contact with gapped graphene sheets is examined. The size-quantization spectrum of charge carriers in an asymmetric quantum well is shown to exhibit a pseudospin splitting. Interface states of a new type arise from the crossing of dispersion curves of gapless and gapped graphene materials. The exciton spectrum is calculated for a planar graphene quantum well. The effect of an external electric field on the exciton spectrum is analyzed.

cond-mat.mes-hall↗
arXiv2012

Boundary States in Graphene Heterojunctions

A new type of states in graphene-based planar heterojunctions has been studied in the envelope wave function approximation. The condition for the formation of these states is the intersection between the dispersion curves of graphene and its gap modification. This type of states can also occur in smooth graphene-based heterojunctions.

cond-mat.mes-hall↗
arXiv2008

Quantum Well Based on Graphene and Narrow-Gap Semiconductors

We consider the energy spectrum of the planar quantum well which consisted of two ribbons of narrow-gap semiconductors and a graphene ribbon between ones. It is shown that the gapless mode appears only in case of inverted narrow-gap semiconductors. Spin splitting of the energy spectrum for a nonsymmetric quantum well is calculated taking into account a specificity of graphene. We investigate interface states and optical transitions. It is shown that the optical transitions are possible only with a conservation of a parity.

cond-mat.other↗
arXiv2008

Planar Heterostructure Graphene -- Narrow-Gap Semiconductor -- Graphene

We investigate a planar heterostructure composed of two graphene films separated by a narrow-gap semiconductor ribbon. We show that there is no the Klein paradox when the Dirac points of the Brillouin zone of graphene are in a band gap of a narrow-gap semiconductor. There is the energy range depending on an angle of incidence, in which the above-barrier damped solution exists. Therefore, this heterostructure is a "filter" transmitting particles in a certain range of angles of incidence upon a potential barrier. We discuss the possibility of an application of this heterostructure as a "switch".

cond-mat.mtrl-sci↗
arXiv2008

Transition of Graphene on a Substrate to a Semimetallic State

Graphene on a substrate has been shown to exhibit a transition, depending on the substrate material, from a zero-gap semiconductor state to a semimetallic state. The ground-state energy of the electron (hole) gas has been calculated within the random-phase approximation.

cond-mat.other↗
arXiv2008

Ground State Energy of Current Carriers in Graphene

The ground state energy of current carriers in graphene considered as a zero-gap semiconductor was calculated in the two-band approximation. The condition of the electronic (hole) system stability in graphene was obtained. The possibility of the zero-gap semiconductor-semimetal transition was discussed.

cond-mat.other↗