arXiv subjects

V. V. Enaldiev

Publications and source records attributed to V. V. Enaldiev.

At least 19 recordsLinked to original sources

arXiv2026

Effect of the local field and dipole-dipole interaction on the spontaneous ordering of dipole moments in bismuth monolayers with an orthorhombic structure

Using two complementary approaches, the instability of bismuth monolayers with an orthorhombic structure with respect to the emergence of spontaneous electric dipole moments at the crystal lattice sites has been studied. The first approach, based on determining the dipole moments of lattice sites through the polarizability of bismuth atoms and taking into account the local Lorentz-Lorenz field, suggests the possibility of the existence of several antiferroelectric and ferroelectric phases in orthorhombic bismuth monolayers. Using the second approach, the vibrational spectrum of a nonpolar symmetric lattice has been analyzed, and two types of soft optical modes corresponding to the ferroelectric and antiferroelectric instabilities of the monolayers have been revealed. The relationship of the Born effective charges to the polarization direction in the ferroelectric phase, as well as their role in the reduction of the frequency of the polar optical phonon, which characterizes the lattice deformation in the ferroelectric phase due to the dipole-dipole interaction, has been shown.

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arXiv2026

Resonant absorption and linear photovoltaic effect in ferroelectric moiré heterostructures

Twisted bilayers, featuring interfacial ferroelectricity in the form of array of polar domains, combined with incommensurate two-dimensional layers in a single van der Waals heterostructures allows for generation of purely electrostatic moiré superlattice potentials in the latter. We study electronic and optoelectronic properties of such heterostructures composed of graphene stacked with the twisted ferroelectric bilayers and show that doping of graphene substantially affects mini-band structures because of screening of free carriers. We demonstrate that formation of van Hove singularities in density of states modifies linear and second-order responses of the structures leading to resonant absorption and linear photovoltaic effect, respectively. The latter is generated solely by a shift photocurrent, arising only with account of virtual optical transitions, whereas an injection photocurrent is forbidden by symmetry.

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arXiv2025

Interplay of interlayer distance and in-plane lattice relaxations in encapsulated twisted bilayers

Encapsulation protects functional layers, ensuring structural stability and improving the quality of assembled van der Waals heterostructures. Here, we develop a model that describes lattice relaxation in twisted bilayers accounting for encapsulation effects, incorporated via a single parameter characterizing rigidity of encapsulation material interfaces. By analysing the twist-angle dependence of weak-to-strong lattice relaxation transition in twisted transition metal dichalcogenide bilayers, we show that increasing interface rigidity raises the crossover twist angle between the two relaxation regimes. Furthermore, tuning this rigidity parameter allows to achieve a good agreement with existing experimental results.

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arXiv2025

Quasi-bound layer-breathing phonons inside perfect dislocations of lattice-relaxed twisted bilayers

Using multiscale modelling we investigate layer-breathing phonons in MX$_2$ bilayers (M=Mo,W; X=S,Se) containing dislocations specific for lattice-relaxed moiré superlattices. The dislocations, forming in the bilayers with parallel and antiparallel alignment of layers, bring about spatial modulation of the interlayer distance, generating effective potentials that promote the emergence of one-dimensional quasi-bound bands of layer-breathing modes inside perfect dislocations. For parallel MX$_2$ bilayers, perfect dislocations host multiple quasi-bound bands, with frequencies above the layer-breathing mode in rhombohedral-stacked domains. In contrast, antiparallel bilayers exhibit only a single quasi-bound band arising for orientations close to the edge-dislocation type, having frequencies above the layer-breathing mode in 2H-stacked domains.

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arXiv2025

Long wavelength interdomain phonons and instability of dislocations in small-angle twisted bilayers

We develop a theory for long wavelength phonons originating at dislocations separating domains in small-angle twisted homobilayers of 2D materials such as graphene and MX$_2$ transition metal dichalcogenides (M=Mo,W; X=S,Se). We find that both partial and perfect dislocations, forming due to lattice relaxation in the twisted bilayers with parallel and anti-parallel alignment of unit cells of the constituent layers, respectively, support several one-dimensional subbands of the {\it interdomain} phonons. We show that spectrum of the lowest gapless subband is characterized by imaginary frequencies, for wave-numbers below a critical value, dependent on the dislocation orientation, which indicates an instability for long enough straight partial and perfect dislocations. We argue that pinning potential and/or small deformations of the dislocations could stabilize the gapless phonon spectra. The other subbands are gapped, with subband bottoms lying below the frequency of interlayer shear mode in domains, which facilitates their detection with the help of optical and magnetotransport techniques.

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arXiv2024

Non-chiral one-dimensional states propagating inside AB/BA domain walls in bilayer graphene

Boundaries between structural twins of bilayer graphene (so-called AB/BA domain walls) are often discussed in terms of the formation of topologically protected valley-polarised chiral states. Here, we show that, depending on the width of the AB/BA boundary, the latter can also support non-chiral one-dimensional (1D) states that are confined to the domain wall at low energies and take the form of quasi-bound states at higher energies, where the 1D bands cross into the two-dimensional spectral continuum. We present the results of modeling of electronic properties of AB/BA domain walls with and without magnetic field as a function of their width and interlayer bias.

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arXiv2024

One-dimensional proximity superconductivity in the quantum Hall regime

Extensive efforts have been undertaken to combine superconductivity and the quantum Hall effect so that Cooper-pair transport between superconducting electrodes in Josephson junctions is mediated by one-dimensional edge states. This interest has been motivated by prospects of finding new physics, including topologically-protected quasiparticles, but also extends into metrology and device applications. So far it has proven challenging to achieve detectable supercurrents through quantum Hall conductors. Here we show that domain walls in minimally twisted bilayer graphene support exceptionally robust proximity superconductivity in the quantum Hall regime, allowing Josephson junctions to operate in fields close to the upper critical field of superconducting electrodes. The critical current is found to be non-oscillatory and practically unchanging over the entire range of quantizing fields, with its value being limited by the quantum conductance of ballistic, strictly one-dimensional electronic channels residing within the domain walls. The system described is unique in its ability to support Andreev bound states at quantizing fields and offers many interesting directions for further exploration.

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arXiv2024

Dislocations in twistronic heterostructures

Long-period moiré superlattices at the twisted interface of van der Waals heterostructures relax into preferential-stacking domains separated by dislocation networks. Here, we develop a mesoscale theory for dislocations in the networks formed in twistronic bilayers with parallel (P) and antiparallel (AP) alignment of unit cells across the twisted interface. For P bilayers we find an exact analytical displacement field across partial dislocations and determine analytic dependences of energy per unit length and width on orientation and microscopic model parameters. For AP bilayers we formulate a semi-analytical approximation for displacement fields across perfect dislocations, establishing parametric dependences for their widths and energies per unit length. In addition, we find regions in parametric space of crystal thicknesses and moiré periods for strong and weak relaxation of moiré pattern in multilayered twistronic heterostructures.

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arXiv2023

Moiré Superstructures in Marginally-Twisted NbSe$_2$ Bilayers

The creation of moiré superlattices in twisted bilayers of two-dimensional crystals has been utilised to engineer quantum material properties in graphene and transition metal dichalcogenide (TMD) semiconductors. Here, we examine the structural relaxation and electronic properties in small-angle twisted bilayers of metallic NbSe$_2$. Reconstruction appears to be particularly strong for misalignment angles $θ_P$ < 2.9$^o$ and $θ_{AP}$ < 1.2$^o$ for parallel (P) and antiparallel (AP) orientation of monolayers' unit cells, respectively. Multiscale modelling reveals the formation of domains and domain walls with distinct stacking, for which density functional theory (DFT) calculations are used to map the shape of the bilayer Fermi surface and the relative phase of the CDW order in adjacent layers. We find a significant modulation of interlayer coupling across the moiré superstructure and the existence of preferred interlayer orientations of the CDW phase, necessitating the nucleation of CDW discommensurations at superlattice domain walls.

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arXiv2023

Twirling and spontaneous symmetry breaking of domain wall networks in lattice-reconstructed heterostructures of 2D materials

Lattice relaxation in twistronic bilayers with close lattice parameters and almost perfect crystallographic alignment of the layers results in the transformation of moiré pattern into a sequence of preferential stacking domains and domain wall networks. Here, we show that reconstructed moiré superlattices of the perfectly aligned heterobilayers of same-chalcogen transition metal dichalcogenides have broken-symmetry structures featuring twisted nodes ('twirls') of domain wall networks. Analysing twist-angle-dependences of strain characteristics for the broken-symmetry structures we show that the formation of twirl reduces amount of hydrostatic strain around the nodes, potentially, reducing their infuence on the band edge energies of electrons and holes.

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arXiv2022

Self-organised quantum dots in marginally twisted MoSe$_2$/WSe$_2$ and MoS$_2$/WS$_2$ bilayers

Moiré superlattices in twistronic heterostructures are a powerful tool for materials engineering. In marginally twisted (small misalignment angle, $θ$) bilayers of nearly lattice-matched two-dimensional (2D) crystals moiré patterns take the form of domains of commensurate stacking, separated by a network of domain walls (NoDW) with strain hot spots at the NoDW nodes. Here, we show that, for type-II transition metal dichalcogenide bilayers MoX$_2$/WX$_2$ (X=S, Se), the hydrostatic strain component in these hot spots creates quantum dots for electrons and holes. We investigate the electron/hole states bound by such objects, discussing their manifestations via the intralayer intraband infrared transitions. The electron/hole confinement, which is strongest for $θ<0.5^{\circ}$, leads to a red-shift of their recombination line producing single photon emitters (SPE) broadly tuneable around 1\,eV by misalignment angle. These self-organised dots can form in bilayers with both aligned and inverted MoX$_2$ and WX$_2$ unit cells, emitting photons with different polarizations. We also find that the hot spots of strain reduce the intralayer MoX$_2$ A-exciton energy, enabling selective population of the quantum dot states.

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arXiv2021

Quasi-stationary near-gate plasmons in van der Waals heterostructures

Near-gate plasmons are a new type of plasma oscillations emerging in homogeneous two-dimensional electron systems where a gate provides partial screening of electron-electron interaction. Here we develop a theory of the near-gate plasmons in van der Waals heterostructures comprising a conducting layer separated by a thin insulator from an uncharged disk-shaped gate. We show that in these structures the near-gate plasmons form gate-size-quantized quasi-stationary discrete modes even in the collisionless limit. Belonging to continuum spectrum of two-dimensional plasmons outside of the disk-gate, the near-gate plasmons are manifested as Fano-like resonances in frequency and magnetodispersions of scattering cross-section of the former scattered off the region under the gate. This enables to recover spectrum of the near-gate plasmons in the van der Waals heterostructures using near-field imaging techniques.

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arXiv2021

A scalable network model for electrically tunable ferroelectric domain structure in twistronic bilayers of two-dimensional semiconductors

Moiré structures in small-angle-twisted bilayers of two-dimensional semiconductors with a broken-symmetry interface form arrays of ferroelectric domains with periodically alternating out-of-plane polarization. Here, we propose a network theory for the tunability of such FE domain structure by applying an electric field perpendicular to the 2D crystal. Using multiscale analysis, we derive a fully parametrized string-theory-like description of the domain wall network and show that it undergoes a qualitative change, after the arcs of partial dislocation like domain walls merge (near the network nodes) into streaks of perfect screw dislocations, which happens at a threshold displacement field dependent on the DWN period.

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arXiv2021

Multifaceted moiré superlattice physics in twisted WSe$_2$ bilayers

Lattice reconstruction in twisted transition-metal dichalcogenide (TMD) bilayers gives rise to piezo- and ferroelectric moiré potentials for electrons and holes, as well as a modulation of the hybridisation across the bilayer. Here, we develop hybrid $\mathbf{k}\cdot \mathbf{p}$ tight-binding models to describe electrons and holes in the relevant valleys of twisted TMD homobilayers with parallel (P) and anti-parallel (AP) orientations of the monolayer unit cells. We apply these models to describe moiré superlattice effects in twisted WSe${}_2$ bilayers, in conjunction with microscopic \emph{ab initio} calculations, and considering the influence of encapsulation, pressure and an electric displacement field. Our analysis takes into account mesoscale lattice relaxation, interlayer hybridisation, piezopotentials, and a weak ferroelectric charge transfer between the layers, and describes a multitude of possibilities offered by this system, depending on the choices of P or AP orientation, twist angle magnitude, and electron/hole valley.

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arXiv2021

Weak ferroelectric charge transfer in layer-asymmetric bilayers of 2D semiconductors

In bilayers of two-dimensional (2D) semiconductors with stacking arrangements which lack inversion symmetry charge transfer between the layers due to layer-asymmetric interband hybridisation can generate a potential difference between the layers. We analyse bilayers of transition metal dichalcogenides (TMDs) - in particular, WSe$_2$ - for which we find a substantial stacking-dependent charge transfer, and InSe, for which the charge transfer is found to be negligibly small. The information obtained about TMDs is then used to map potentials generated by the interlayer charge transfer across the moiré superlattice in twistronic bilayers.

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arXiv2021

Piezoelectric networks and ferroelectric moiré superlattice domains in twistronic WS$_2$/MoS$_2$ and WSe$_2$/MoSe$_2$ bilayers

Twistronic van der Waals heterostrutures offer exciting opportunities for engineering optoelectronic properties of nanomaterials. Here, we use multiscale modeling to study trapping of charge carriers and excitons by ferroelectric polarisation and piezoelectric charges by domain structures in twistronic WX$_2$/MoX$_2$ bilayers (X=S,Se). For almost aligned 2H-type bilayers, we find that holes and electrons are trapped in the opposite -- WMo and XX (tungsten over molybdenum {\it versus} overlaying chalcogens) -- corners of the honeycomb domain wall network, swapping their position at a twist angle $0.2^{\circ}$, with XX corners providing $30$\,meV deep traps for the interlayer excitons for all angles. In 3R-type bilayers, both electrons and holes are trapped in triangular "3R stacking" domains, where WX$_2$ chalcogens set over MoX$_2$ molybdenums, which act as $130$\,meV deep quantum boxes for interlayer excitons for twist angles $\lesssim 1^{\circ}$, for larger angles shifting towards domain wall network XX stacking sites.

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arXiv2020

Stacking domains and dislocation networks in marginally twisted bilayers of transition metal dichalcogenides

We apply a multiscale modeling approach to study lattice reconstruction in marginally twisted bilayers of transition metal dichalcogenides (TMD). For this, we develop DFT-parametrized interpolation formulae for interlayer adhesion energies of MoSe$_2$, WSe$_2$, MoS$_2$, and WS$_2$, combine those with elasticity theory, and analyze the bilayer lattice relaxation into mesoscale domain structures. Paying particular attention to the inversion asymmetry of TMD monolayers, we show that 3R and 2H stacking domains, separated by a network of dislocations develop for twist angles $θ^{\circ}<θ^{\circ}_P\sim 2.5^{\circ}$ and $θ^{\circ}<θ^{\circ}_{AP}\sim 1^{\circ}$ for, respectively, bilayers with parallel (P) and antiparallel (AP) orientation of the monolayer unit cells and suggest how the domain structures would manifest itself in local probe scanning of marginally twisted P- and AP-bilayers.

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arXiv2018

Collective excitations in two-component one-dimensional massless Dirac plasma

We study spectra of long wavelength plasma oscillations in a system of two energy splitted one-dimensional (1D) massless Dirac fermion subbands coupled by spin-orbit interaction. Such a system may be formed by edge subbands in semiconducting transition metal dichalcogenide monolayers. Intrasubband transitions of massless Dirac fermions give rise to optical and acoustic gapless branches of intrasubband 1D plasmons. We reveal that the optical branch is of quantum character with group velocity being inverse proportional to square root of the Planck constant, whereas the acoustic branch is classical one with group velocity proportional to geometric mean of the edge subband velocities. Spin-orbit interaction, allowing intersubband transitions in the system, results in emergence of two branches of intersubband 1D plasmons: upper and lower ones. The upper and lower branches are gapped at small wave vectors and evolve with positive and negative group velocities, respectively, from energy splitting of the edge subbands at Fermi-level. The both intersubband branches adjoin intersubband single particle excitation continuum from above, while in case of the edge subbands with unequal velocities the lower one experiences Landau damping at small wave vectors. In addition, the lower branch, attaining zero frequency at a non-zero wave vector, alters its group velocity from negative to positive one.

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