Vyacheslav M. Silkin’s research while affiliated with Donostia International Physics Center and other places

Plasmonic nanocavities offer exceptional confinement of light, making them effective for energy conversion applications. However, limitations with stability, materials, and chemical activity have impeded their practical implementation. Here we integrate ultrathin palladium (Pd) metal films from sub- to few- atomic monolayers inside plasmonic nanocavities using underpotential deposition. Despite the poor plasmonic properties of bulk Pd in the visible region, minimal loss in optical field enhancement is delivered along with Pd chemical enhancement, as confirmed by ab initio calculations. Such synergistic effects significantly enhance photocatalytic activity of the plasmonic nanocavities as well as photostability by suppressing surface atom migration. We show the atomic alchemical-glazing approach is general for a range of catalytic metals that bridge plasmonic and chemical catalysis, yielding broad applications in photocatalysis for optimal chemical transformation.

In this study, we analyse the dynamic dielectric response function of high-Tc cuprates as a function of the doping level, taking into account the full energy band dispersion of the CuO2 conducting band. We observe that there are three anomalous branches within the plasmon spectrum in addition to the well-known conventional two-dimensional gapless plasmon mode. Two of these branches correspond to overdamped modes, namely hyperplasmons, while the third one corresponds to an almost one-dimensional plasmon mode. We show that these branches appear as a result of the peculiarities of the electronic spectra of cuprates. Furthermore, we investigated the effect of the doping on these modes. Our analysis demonstrates that in the doping level range close to the optimal doping level, the properties of all three modes undergo a significant transformation. The results could help us unlock the mystery of normal state of cuprates.

We suggest the method for direct ab initio calculation of magnons in complex collinear magnets. The method is based on the density-functional-theory calculation under two different constraints: one constraint governs the change of the magnetization with respect to the ground state, and the other is the symmetry constraint responsible for the value of the magnon wave vector. The performance of the method is demonstrated by the application to an altermagnet MnTe. An important role in both the formulation and the application of the method play the aspects of generalized symmetry described by the spin-space groups. The symmetry analysis connects in one coherent picture the following three parts of the consideration: (i) the generalized translational symmetry of the magnons as a crucial condition for their efficient ab-initio calculation, (ii) altermagnetic spin-splitting of the electron states in the ground magnetic state, and (iii) chirality splitting of the magnon excitations. It is demonstrated that both the spin splitting of the electron states and the chirality splitting of the magnons have identical patterns in the corresponding wave vector spaces. Since the altermagnetism of MnTe is the consequence of the presence of the Te atoms, an adequate attention is devoted to the symmetry analysis and calculation results for the Te moments induced in the magnon states. The knowledge of the symmetry properties of the Te moments allows to accelerate the numerical convergence of the magnon states and serves as a test for the accuracy of the calculations. To expose the connection between electron band structures of the magnon states of the system and the chirality properties of these states we investigate the transformation of the electron structure in the transition from the collinear ground state to a noncollinear magnon state.

Nowadays, the application of protective multicomponent coatings based on hard metal nitrides is increasingly used to increase the resistance of structures and tools to wear, corrosion, and oxidation. In the present work, the multicomponent system Ti-Al-Ta-Si-N is studied, which has high hardness and crack resistance combined with thermal stability and oxidation resistance. The process of formation of the nanocrystalline structure of the coating during its deposition on materials plays a key role in the optimization of these properties. The nanocrystalline structure of the coating is formed due to Si impurity, which is poorly soluble in the Ti1−x−yAlxTayN system based on B1-TiN and segregates mainly along grain boundaries, forming grain boundary amorphous phases of SizN type. In order to find the optimal composition of multicomponent coatings with improved physical and mechanical properties, it is necessary to understand the peculiarities of interaction of Si impurity with the surface of B1-TiN phase in the presence of Al and Ta substitutional impurities. In the present work, with the help of first-principles calculations of electronic and atomic structure of (001) and (111) surfaces of the Ti1−x−yAlxTayN system with adsorbed Si atom and the interatomic bond study apparatus based on the calculation of a crystal orbital Hamilton population and a crystal orbital bond index, the nature of the bonds between adsorbed Si and the N, Ti, Al, and Ta atoms of the Ti1−x−yAlxTayN surface system has been studied. It was found that the binding energy of Si with the Ti1−x−yAlxTayN surface system can be both higher and lower than the binding energy of its bonding with the surface of the binary TiN compound depending on the position of the Al and Ta substitution atoms in the surface layers. The Si bonding with the atoms of the Ti1−x−yAlxTayN surface is ionic–covalent in nature. It is shown that the Si-Ta interaction has the highest degree of covalency and strength, and the Si-Al interaction is predominantly ionic in most cases considered and is weaker than the Si-Ti and Si-N bonds. Impurity atoms of Al or Ta have very little effect on the Si-Ti and Si-N bonds due to the local nature of the bonds in the Ti1−x−yAlxTayN surface system with adsorbed silicon atoms.

A narrow frequency bandwidth of epsilon-near-zero metamaterials limits the use of many optical, microwave, and electronic devices. In this paper, we propose a recipe to broaden the operational bandwidth by employing a structure of properly tailored square frames nested within each other. To illustrate this effect, we derive the effective permittivity for the considered frame geometry. Then, we show that combining constituent materials with loss and materials with gain enables us to achieve the effective permittivity over a frequency band as small as desired. This technique may prove valuable for various applications including invisibility cloaks, camouflage, shielding, and sensorics.

Nowadays, the application of protective multicomponent coatings based on hard metal nitrides is increasingly used to increase the resistance of structures and tools to wear, corrosion and oxidation. In the present work, the multicomponent system Ti-Al-Ta-Si-N is studied, which has high hardness and crack resistance combined with thermal stability and oxidation resistance. The process of formation of the nanocrystalline structure of the coating during its deposition on mate-rials plays a key role in the optimization of these properties. The nanocrystalline structure of the coating is formed due to Si impurity, which is poorly soluble in the Ti1−x−yAlxTayN system based on B1-TiN and segregates mainly along grain boundaries, forming grain boundary amorphous phases of SizN type. In order to find the optimal composition of multicomponent coatings with improved physical and mechanical properties, it is necessary to understand the peculiarities of interaction of Si impurity with the surface of B1-TiN phase in the presence of Al and Ta substitutional impurities. In the present work with the help of first-principles calculations of electronic and atomic structure of (001) and (111) surfaces of the Ti1−x−yAlxTayN system with adsorbed Si atom and interatomic bond study apparatus based on the calculation of a Crystal Orbital Hamilton Population and a Crystal Orbital Bond Index, the nature of the bonds between adsorbed Si and N, Ti, Al, Ta atoms of the Ti1−x−yAlxTayN surface system has been studied. It was found that the binding energy of Si with the Ti1−x−yAlxTayN surface system can be both higher and lower than the binding energy of its bonding with the surface of the binary TiN compound depending on the position of the Al and Ta substitu-tion atoms in the surface layers. The Si bonding with the atoms of the Ti1−x−yAlxTayN surface is ionic-covalent in nature. It is shown that the Si-Ta interaction has the highest degree of covalency and strength and the Si-Al interaction is predominantly ionic in most cases considered and is weaker than the Si-Ti and Si-N bonds. Impurity atoms of Al or Ta have very little effect on the Si-Ti and Si-N bonds due to the local nature of the bonds in the Ti1−x−yAlxTayN surface system with ad-sorbed silicon atom.

In this study, we analyze the dielectric function of high-Tc cuprates as a function of doping level, taking into account the full energy band dispersion within the CuO$_2$ monolayer. In addition to the conventional two-dimensional (2D) gapless plasmon mode, our findings reveal the existence of three anomalous branches within the plasmon spectrum. Two of these branches are overdamped modes, designated as hyperplasmons, and the third is an almost one-dimensional plasmon mode (1DP). We derive an analytic expression for dynamic part of the response function. Furthermore, we investigated the effect of the doping on these modes. Our analysis demonstrates that in the doping level range close to the optimal doping level, the properties of all three modes undergo a significant transformation.

By minimizing, in the L2 norm, the difference between the left- and the right-hand sides of the time-dependent Schrödinger equation, the variational principle of McLachlan (McLVP) [A. McLachlan, Mol. Phys. 8, 39 (1964)] provides a powerful tool for the generation of equations of motion. If the trial wave function is the Slater determinant, McLVP produces a temporally and spatially nonlocal exchange potential [V. U. Nazarov, Phys. Rev. B 87, 165125 (2013)]. We study the performance of the corresponding wave-vector and frequency-dependent exchange kernel fxh(q,ω) of the homogeneous electron liquid. While the McLVP-based fxh(q,ω) lacks correlations by construction, we find that it accurately accounts for exchange, reproducing features in the quantum Monte Carlo data, which the known constraint-based kernels miss. We argue that the complementary use of the McLVP- and the constraint-based exchange-correlation kernels will enhance the performance of the linear-response time-dependent density functional theory of the electron liquid.

By minimizing, in the $L_2$ norm, the difference between the left- and the right-hand sides of the time-dependent Schr\"{o}dinger equation, the variational principle of McLachlan (McLVP) [A. McLachlan, Molecular Physics {\bf 8}, 39 (1964)] provides a powerful tool for the generation of equations of motion. If the trial wave function is the Slater determinant, McLVP produces a temporally and spatially nonlocal exchange potential [V. U. Nazarov, Phys. Rev. B {\bf 87}, 165125 (2013)]. We study the performance of the corresponding wave-vector and frequency-dependent exchange kernel $f^h_x(q,\omega)$ of the homogeneous electron liquid. While the McLVP-based $f^h_x(q,\omega)$ lacks correlations by construction, we find that it accurately accounts for exchange, reproducing features in the quantum Monte Carlo data, which the known constraint-based kernels miss. We argue that the complementary use of the McLVP- and the constraint-based exchange-correlation kernels will enhance the performance of the linear response time-dependent density functional theory of the electron liquid.