arXiv subjects

Yuriy Dedkov

Publications and source records attributed to Yuriy Dedkov.

At least 19 recordsLinked to original sources

arXiv2024

Electronic Correlations in Multiferroic van der Waals CuCrP$_2$S6: Insights From X-Ray Spectroscopy and DFT

The electronic structure of high-quality van der Waals multiferroic CuCrP$_2$S6 crystals was investigated applying photoelectron spectroscopy methods in combination with DFT analysis. Using X-ray photoelectron and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at the Cu L2,3 and Cr L2,3 absorption edges we determine the charge states of ions in the studied compound. Analyzing the systematic NEXAFS and resonant photoelectron spectroscopy data at the Cu/Cr L2,3 absorption edges allowed us to assign the CuCrP$_2$S6 material to a Mott-Hubbard type insulator and identify different Auger-decay channels (participator vs. spectator) during absorption and autoionization processes. Spectroscopic and theoretical data obtained for CuCrP$_2$S6 are very important for the detailed understanding of the electronic structure and electron-correlations phenomena in different layered materials, that will drive their further applications in different areas, like electronics, spintronics, sensing, and catalysis.

cond-mat.mtrl-sci↗

arXiv2022

Realization of the electric-field driven "one-material"-based magnetic tunnel junction using van der Waals antiferromagnetic MnPX3 (X: S, Se)

Presently a lot of efforts are devoted to the investigation of new two-dimensional magnetic materials, which are considered as promising for the realization of the future electronics and spintronics devices. However, the utilization of these materials in different junctions requires complicated processing that in many cases leads to unwanted parasitic effects influencing the performance of the junctions. Here, we propose the new elegant approach for the realization of the "one-material"-based magnetic tunnel junction. The several layers of 2D van der Waals MnPX3 (X: S, Se), which is insulating antiferromagnet in its ground state, are used and the effect of the applied external electric filed leads to the half-metallic ferromagnetic states for the outermost layers of the MnPX3 stack. The rich states diagram of such magnetic tunnel junction permits to precisely control its tunneling conductivity. The realized "one-material"-based magnetic tunnel junction allows to avoid all effects connected with the lattice mismatches and carriers scattering effects at the materials interfaces, giving high perspectives for the application of such systems in electronics and spintronics.

cond-mat.mtrl-sci↗

arXiv2021

Adsorption of water on the pristine and defective semiconducting 2D CrPX$_3$ monolayers (X: S, Se)

The effect of vacancy and water adsorption on the electronic structure of semiconducting 2D trichalcogenide material CrPX$_3$ (X: S, Se) is studied using state-of-the-art density functional theory (DFT) approach. It is found that chalcogen vacancies play a minor role on the electronic structure of CrPX$_3$ in the vicinity of the Fermi level leading to the slightly reduced band gap for these materials, however, inducing strongly localised defect states which are placed in the energy gap formed by the valence band states. Our DFT calculations show that the interaction of water molecules with CrPX$_3$, pristine and defective, can be described as physisorption and the adsorption energy for H$_2$O is insensitive to the difference between pristine and chalcogen-defective surface of trichalcogenide material. These results are the first steps for the theoretical description of the ambient molecules interaction with 2D semiconducting CrPX$_3$ material, that is important for its future experimental studies and possible applications.

cond-mat.mtrl-sci↗

arXiv2021

Mott-Hubbard Insulating State for the Layered van der Waals FePX$_3$ (X:S, Se) As Revealed by NEXAFS and Resonant Photoelectron Spectroscopy

A broad family of the nowadays studied low-dimensional systems, including 2D materials, demonstrate many fascinating properties, which however depend on the atomic composition as well as on the system dimensionality. Therefore, the studies of the electronic correlation effects in the new 2D materials is of paramount importance for the understanding of their transport, optical and catalytic properties. Here, by means of electron spectroscopy methods in combination with density functional theory calculations we investigate the electronic structure of a new layered van der Waals FePX$_3$ (X: S, Se) materials. Using systematic resonant photoelectron spectroscopy studies we observed strong resonant behavior for the peaks associated with the $3d^{n-1}$ final state at low binding energies for these materials. Such observations clearly assign FePX$_3$ to the class of Mott-Hubbard type insulators for which the top of the valence band is formed by the hybrid Fe-S/Se electronic states. These observations are important for the deep understanding of this new class of materials and draw perspectives for their further applications in different application areas, like (opto)spintronics and catalysis.

cond-mat.mtrl-sci↗

arXiv2021

Dirac fermions in half-metallic ferromagnetic mixed Cr$_{1\textrm{-}x}$M$_x$PSe$_3$ monolayers

The electronic and magnetic properties of pristine CrPSe$_3$ and mixed Cr$_{1\textrm{-}x}$M$_x$PSe$_3$ (M = Zn, Cd, Hg) monolayers were studied using density functional theory including an on-site Coulomb term (DFT$+U$) and tight-binding approach (TBA). While pristine CrPSe$_3$ monolayer has an antiferromagnetic (AFM) ground state, its alloying with MPSe$_3$ may give rise to half-metallic ferromagnet (HMF) with high Curie temperature. The resulting monolayers demonstrate single-spin Dirac cones of mainly Cr-$d$ character located in the first Brillouin zone directly at the Fermi energy. The calculated Fermi velocities of Dirac fermions indicate very high mobility in mixed Cr$_{1\textrm{-}x}$M$_x$PSe$_3$ monolayers, that makes this material appealing for low-dimensional spintronics applications.

cond-mat.mtrl-sci↗

arXiv2021

Adsorption of water molecules on pristine and defective NiPX$_3$ (X: S, Se) monolayers

Layered transition metal trichalcogenides MPX$_3$ (M: transition metal; X: S, Se) demonstrate a wide spectrum of properties and are widely proposed as effective materials for the water splitting reactions. Among these materials, NiPX$_3$ are the most promising ones due to the match their electronic structures for the oxygen and hydrogen evolution reactions. Here, we present first steps of a detailed theoretical description on the adsorption of water molecules on pristine and defected (chalcogen vacancies) surfaces of NiPX$_3$ and show that in all cases a physisorption takes the place with adsorption energies do not exceeding $-650$\,meV and water dissociative adsorption is unfavourable. This work provides a general description for water molecules interaction with MPX$_3$ and can serve as a basis for further studies on more complicated water/MPX$_3$ reactions.

cond-mat.mtrl-sci↗

arXiv2021

Modification of the magnetic and electronic properties of the graphene-Ni(111) interface via halogens intercalation

Electronic decoupling of graphene from metallic and semiconducting substrates via intercalation of different species is one of the widely used approaches in studies of graphene. In the present work the modification of the electronic and magnetic properties of graphene on ferromagnetic Ni(111) layer via intercalation of halogen atoms (X = F, Cl, Br) is studied using the state-of-the-art density-functional theory approach. It is found that in all gr/X/Ni(111) intercalation systems a graphene layer is fully electronically decoupled from the ferromagnetic substrate; however, different kind (electron or hole) and level of doping can be achieved. Despite the extremely small magnetic moment of C-atoms in graphene observed after halogens intercalation, the sizeable spin-splitting up to $35$ meV for the linearly dispersing graphene $\pi$ bands is found. The obtained theoretical data bring new ideas on the formation of the graphene-ferromagnet interfaces where spin polarized free-standing graphene layer can be formed with the possible application of these systems in electronics and spintronics.

cond-mat.mtrl-sci↗

arXiv2021

To the synthesis and characterization of layered metal phosphorus triselenides proposed for electrochemical sensing and energy applications

Recent studies reported on the synthesis and characterization of several bulk crystals of layered metal triselenophosphites MPSe$_3$ (M = transition metals). In these works characterization was performed via a combination of different bulk- and surface-sensitive experimental methods accompanied by DFT calculations. However, the critical examination of the available experimental and theoretical data demonstrates that these results do not support the conclusions on the electrochemical sensing and energy applications of studied triselenophosphites. These conclusions are made without any relation to the age of discussed data and possible recent progress in experimental and theoretical approaches.

cond-mat.mtrl-sci↗

arXiv2021

Graphene Layer Morphology as an Indicator of the Metals Alloy Formation at the Interface

The intercalation of different species in graphene-metal interfaces is widely used to stabilise the artificial phases of different materials. However, formation of the surface alloys upon the guest-metal intercalation is still an open question, which is very important for the fabrication of graphene-based interfaces with desired properties. Here, the widely studied interfaces of graphene with Ru(0001) and Ir(111) were modified using intercalation of a thin Mn layer and investigated by means of scanning tunnelling microscopy (STM) accompanied by density functional theory (DFT) calculations, which reproduce the observed experimental data. It is found that Mn forms a pseudomorphic layer on Ru(0001) under a strongly buckled graphene layer. In case of Mn intercalation in graphene/Ir(111), a buried thin layer of MnIr alloy is formed beneath the first Ir layer under a flat graphene layer. This unexpected observation is explained on the basis of phase diagram pictures for the Mn-Ru and Mn-Ir systems as well as via comparison of calculated total energies for the respective interfaces. Our results shed light on the understanding of mechanisms of the alloys formation at the graphene-metal interfaces and demonstrate their potential for the preparation of tailored interfaces for future graphene-based applications.

cond-mat.mtrl-sci↗

arXiv2021

Correlations in the Electronic Structure of van der Waals NiPS$_3$ Crystals: An X-Ray Absorption and Resonant Photoelectron Spectroscopy Study

The electronic structure of high-quality van der Waals NiPS$_3$ crystals was studied using near-edge x-ray absorption spectroscopy (NEXAFS) and resonant photoelectron spectroscopy (ResPES) in combination with density functional theory (DFT) approach. The experimental spectroscopic methods, being element specific, allow to discriminate between atomic contributions in the valence and conduction band density of states and give direct comparison with the results of DFT calculations. Analysis of the NEXAFS and ResPES data allows to identify the NiPS$_3$ material as a charge-transfer insulator. Obtained spectroscopic and theoretical data are very important for the consideration of possible correlated-electron phenomena in such transition-metal layered materials, where the interplay between different degrees of freedom for electrons defines their electronic properties, allowing to understand their optical and transport properties and to propose further possible applications in electronics, spintronics and catalysis.

cond-mat.mtrl-sci↗

arXiv2021

Topological Quasi-2D Semimetal Co$_3$Sn$_2$S$_2$: Insights To Electronic Structure From NEXAFS and Resonant Photoelectron Spectroscopy

The electronic structure of the natural topological semimetal Co$_3$Sn$_2$S$_2$ crystals was studied using near-edge x-ray absorption spectroscopy (NEXAFS) and resonant photoelectron spectroscopy (ResPES). Although, the significant increase of the Co\,$3d$ valence band emission is observed at the Co\,$2p$ absorption edge in the ResPES experiments, the spectral weight at these photon energies is dominated by the normal Auger contribution. This observation indicates the delocalised character of photoexcited Co\,$3d$ electrons and is supported by the first-principle calculations. Our results on the investigations of the element- and orbital-specific electronic states near the Fermi level of Co$_3$Sn$_2$S$_2$ are of importance for the comprehensive description of the electronic structure of this materials, which is significant for future applications of this material in different areas of science and technology, including catalysis and water splitting applications.

cond-mat.mtrl-sci↗

arXiv2021

Intercalation of Mn in graphene/Cu(111) interface: insights to the electronic and magnetic properties from theory

The effect of Mn intercalation on the atomic, electronic and magnetic structure of the graphene/Cu(111) interface is studied using state-of-the-art density functional theory calculations. Different structural models of the graphene-Mn-Cu(111) interface are investigated. While a Mn monolayer placed between graphene and Cu(111) (an unfavorable configuration) yields massive rearrangement of the graphene-derived $\pi$ bands in the vicinity of the Fermi level, the possible formation of a Cu$_2$Mn alloy at the interface (a favorable configuration) preserves the linear dispersion for these bands. The deep analysis of the electronic states around the Dirac point for the graphene/Cu$_2$Mn/Cu(111) system allows to discriminate between contributions from three carbon sublattices of a graphene graphene layer in this system and to explain the bands' as well as spins' topology of the electronic states around the Fermi level.

cond-mat.mtrl-sci↗

arXiv2021

Electronic, magnetic and optical properties of MnPX$_3$ (X = S, Se) monolayers with and without chalcogen defects: A first-principle study

Based on density functional theory (DFT), we performed first-principle studies on the electronic structure, magnetic state and optical properties of two-dimensional (2D) transition-metal phosphorous trichalcogenide MnPX$_3$ (X=S and Se). The calculated interlayer cleavage energies of MnPX$_3$ monolayers indicate the energetic possibility to be exfoliated from bulk phase, with good dynamical stability confirmed by the absence of the imaginary contributions in the phonon spectra. MnPX$_3$ monolayers are both N\'eel antiferromagnetic (AFM) semiconductors with direct band gaps falling into the visible optical spectrum. Magnetic interaction parameters were extracted within the Heisenberg model to investigate the origin of the AFM state. Three in-plane magnetic exchange parameters play important role in the robust AFM configuration of Mn ions. The N\'eel temperatures ($T_\mathrm{N}$) were estimated by means of Monte Carlo simulations, obtaining the theoretical $T_\mathrm{N}$ of $103$\,K and $80$\,K for 2D MnPS$_3$ and MnPSe$_3$, respectively. With high spin state, Mn ions arranged in honeycomb lattices, the spin-degenerated band structures exhibit valley polarisation and was investigated in different biaxial in-plain strains, considering the spin-orbital coupling (SOC). 2D MnPX$_3$ monolayers show excellent performance on the optical properties, and the absorption spectra were discussed in detail to find the transition mechanism. Different amount and configuration of chalcogen vacancy were introduced into the MnPX$_3$ monolayers, and it is found that the electronic structures are heavily affected depending on the vacancy geometric structure, leading to different magnetic state and absorption spectra of defected MnPX$_3$ systems.

cond-mat.mtrl-sci↗

arXiv2020

Epitaxial graphene/Ge interfaces: a minireview

The recent discovery of the ability to perform direct epitaxial growth of graphene layers on semiconductor Ge surfaces led to the huge interest to this topic. One of the reasons for this interest is the chance to overcome several present-day drawbacks on the way of the graphene integration in the modern semiconductor technology. The other one is connected with the fundamental studies of the new graphene-semiconductor interfaces, that might help with the deeper understanding of mechanisms, which governs graphene growth on different substrates as well as shed light on the interaction of graphene with these substrates, which range is now spread from metals to insulators. The present minireview gives a timely overview of the state-of-the-art in the field of studies of the graphene-Ge epitaxial interfaces and draw some perspective directions in this research area.

cond-mat.mtrl-sci↗

arXiv2019

Intercalation of O$_2$ and N$_2$ in the Graphene/Ni Interfaces of Different Morphology

Near-ambient pressure XPS and STM experiments are performed to study the intercalation of oxygen and nitrogen at different partial gas pressures and different temperatures in the graphene/Ni/Ir(111) system of different morphologies. We performed detailed experiments on the investigation of the chemical state and topography of graphene, before and after gas intercalation, depending on the amount of pre-intercalated Ni in graphene/Ir(111). It is found that only oxygen can be intercalated under graphene in all considered cases, indicating the role of the intra-molecular bonding strength and possibility of gas molecules dissociation on different metallic surfaces on the principal possibility and on the mechanism of intercalation of different species under graphene.

cond-mat.mtrl-sci↗

arXiv2019

Dirac-Electron Behavior for Spin-Up Electrons in Strongly Interacting Graphene on Ferromagnetic Mn$_5$Ge$_3$

An elegant approach on the synthesis of graphene on the strong ferromagnetic (FM) material Mn$_5$Ge$_3$ is proposed via intercalation of Mn in the graphene-Ge(111) interface. According to the DFT calculations, graphene in this strongly interacting system demonstrates the large exchange splitting of the graphene-derived $\pi$ band. In this case only spin-up electrons in graphene preserve the Dirac-electron-like character in the vicinity of the Fermi level and the K point, whereas such behavior is not detected for the spin-down electrons. This unique feature of the studied gr/FM-Mn$_5$Ge$_3$ interface which can be prepared on the semiconducting Ge can lead to its application in spintronics.

cond-mat.mtrl-sci↗

arXiv2019

Electronic structure and magnetic properties of the graphene/Ni3Mn/Ni(111) trilayer

Experimental and theoretical studies of manganese deposition on graphene/Ni(111) shows that a thin ferromagnetic Ni3Mn layer, which is protected by the graphene overlayer, is formed upon Mn intercalation. The electronic bands of graphene are affected by Ni3Mn interlayer formation through a slight reduction of n-type doping compared to graphene/Ni(111) and a suppression of the interface states characteristic of graphene/Ni(111). Our DFT-based theoretical analysis of interface geometric, electronic, and magnetic structure gives strong support to our interpretation of the experimental scanning tunneling microscopy, low energy electron diffraction, and photoemission results, and shows that the magnetic structure of graphene is strongly influenced by Ni3Mn formation.

cond-mat.mtrl-sci↗

arXiv2018

Realistic large-scale modeling of Rashba and induced spin-orbit effects in graphene/high-Z-metal systems

Graphene, as a material with a small intrinsic spin-orbit interaction of approximately 1 $\mu$eV, has a limited application in spintronics. Adsorption of graphene on the surfaces of heavy-metals was proposed to induce the strong spin-splitting of the graphene $\pi$-bands either via Rashba effect or due to the induced spin-orbit effects via hybridization of the valence band states of graphene and metal. The spin-resolved photoelectron spectroscopy experiments performed on graphene adsorbed on the substrates containing heavy elements demonstrate the "giant" spin-splitting of the $\pi$ states of the order of 100 meV in the vicinity of the Fermi level ($E_F$) and the K point. However, the recent scanning tunneling spectroscopy experiments did not confirm these findings, leaving the fact of the observation of the "giant" Rashba effect or induced spin-orbit interaction in graphene still open. Thus, a detailed understanding of the physics in such systems is indispensable. From a theory side this requires, first of all, correct modeling of the graphene/metal interfaces under study. Here we present realistic super-cell density-functional theory calculations, including dispersion interaction and spin-orbit interaction, for several graphene/high-Z-metal interfaces. While correctly reproduce the spin-splitting features of the metallic surfaces, their modifications under graphene adsorption and doping level of graphene, our studies reveal that neither "giant" Rashba- nor spin-orbit induced splitting of the graphene pi states around $E_F$ take place.

cond-mat.mtrl-sci↗