Main achievements in 2024

Material for ultraviolet, visible, and infrared optics

N.N. Kolesnikov, A.S. Azhgalieva, B.S. Redkin et al.

Within the exploratory study aimed at creating materials that are transparent in a wide wavelength range and have a low refractive index, we have proposed and patented a new material K₅Gd_(1-x)Ho_x(MoO₄)₄ (x=0.04-0.06) for ultraviolet, visible, and infrared optics [1-2]. This material can be produced in the form of single crystals (Fig. 1), is easy to process, is non-hygroscopic, and has a very wide transparency region corresponding to wavelengths from 0.3 to 5.5 μm. The transmission in this range exceeds 80 % (Figs. 2 and 3) for the thickness of polished samples of 2 mm.

Figure 1. K5Gd(1-x)Hox(MoO4)4 single crystal cleaved along the cleavage	Figure 2. Transmission spectrum of UV, visible, and near-IR radiation of single-crystal K5Gd(1-x)Hox(MoO4)4 (transmittance in %, wavelength in µm)	IR transmission spectrum of single-crystal K5Gd(1-x)Hox(MoO4)4 (transmittance in %, wavelength in µm)

K₅Gd_(1-x)Ho_x(MoO₄)₄ single crystals can be viewed as a promising material for laser optics, particularly UV laser optics. The material proposed can also be applied in optical devices operating in a wide wavelength range.

Publications:

1. N.N. Kolesnikov, A.S. Azhgalieva, B.S. Redkin, V.A. Morozov, B.I. Lazoryak. Material for ultraviolet, visible, and infrared optics. Patent for invention no. 2826665, Russian Federation. Priority date: 14.06.2024, recorded in the state register of the Russian Federation on 16.09.2024, published on 16.09.2024, Bul. no. 26.
2. Diploma of ISSP RAS for the promising development “Material for ultraviolet, visible, and infrared optics” presented at the 27th International Exhibition of Chemical Industry and Science “Chemistry-2024”, Moscow, October 21-24, 2024.

State task of ISSP RAS: “Physics and Technologies of New Materials and Prospective Structures”, no. 122040600127-3 Physical Sciences, branch 1.3.2.10. “Physical Materials Science and Physics of Defects”

Ordered one-dimensional structures of topological defects on the nematic–isotropic liquid surface

P.V. Dolganov, N.A. Spiridenko, V.K. Dolganov
Head: senior researcher, D.Sc. P.V. Dolganov

The investigation of topological defects, their structure and collective behavior is one of the most important areas of condensed matter physics. Before this work, studies were carried out on two-dimensional and partially on three-dimensional structures.

In this work, ordered one-dimensional structures of topological defects were obtained for the first time, and their structure was determined. The end effects were eliminated by closing linear structures into closed chains of defects (“necklaces”, Fig. (a)).

The collective behavior and dynamics of defects in a one-dimensional structure and the change in their number due to the pairwise annihilation of defects with +1 and -1 topological charges were studied for the first time. It was shown that the observed behavior differed drastically from the behavior of two-dimensional and three-dimensional structures. For the first time, toroidal isotropic droplets were obtained in a thermotropic nematic with and without (Fig. (c)) topological defects as a result of a topological transition with a change in the Euler characteristic.

Topological defects were obtained on the surface that separated a nematic liquid crystal and an isotropic liquid. The defects were formed due to competing boundary conditions of the nematic at the interface with the isotropic liquid and on the cell surface. The structure of the chains was determined using polarizing optical microscopy. It was shown that the chains were formed by alternating defects with +1 and -1 topological charges. The total topological charge of the chain was zero, which agrees with the Euler characteristic of the surface. A method for obtaining chains with a central cluster of topological defects was developed (Fig. (b)). Toroidal structures were formed spontaneously with a change in temperature.

Figure. (a) “Necklace” of topological defects. (b) Chain of defects with a central cluster. (c) Isotropic toroid in a nematic liquid crystal.

Publication: Dolganov, P.V. Ordered structures formed by nematic topological defects and their transformation with changing the Euler characteristics / P.V. Dolganov, N.A. Spiridenko, V.K. Dolganov // Physical Review E. – 2024. – Vol. 110, Iss. 2. – P. 24703. – DOI:10.1103/PhysRevE.110.024703

RSF project no. 23-12-00200

Physical Sciences, branch 1.3.2.6. “Physics of Surfaces, Interfaces, and Other Extended Defects”

Crossover from relativistic to non-relativistic magnetization for the altermagnetic state realized in the MnTe semiconductor

N.N. Orlova, A.A. Avakyants, N.N. Kolesnikov, A.V. Timonina, E.V. Deviatov

Recently, attention has been drawn to systems where spin-momentum locking characteristic of topological insulators and topological semimetals extends to the case of conventional, non-relativistic groups of magnetic symmetry. In this case, a new class of magnetic materials is added to conventional ferro- and antiferromagnets. This is altermagnetics, in which, at low total magnetization, spin polarization occurs that alternates in the k-space. Since the introduction of this class in 2022, a significant number of theoretical works have appeared that predict various physical effects. However, their experimental implementation remains challenging.

In this work, we carried out direct precision studies of the angular dependence of magnetization for thin flakes of single-crystal MnTe. Above 85 K, we confirmed the antiferromagnetic behavior of the magnetization, which is known for α-MnTe. Below 85 K, we found anomalous low-field magnetization behavior, which was accompanied by the complex angular dependence of the magnetization: 180° oscillation periodicity in low fields, which is characteristic of ferromagnets, was replaced by 90° periodicity in high fields, with the interplay between the minima and maxima at intermediate values of magnetic fields, see Fig. 1. This angular dependence cannot be expected for conventional ferro- and antiferromagnetic systems. At the same time, total magnetization can arise in altermagnets only if there is a weak but finite spin-orbit interaction, which, in turn, can be suppressed by a magnetic field or temperature. Hence, our experiment directly confirms altermagnetism in MnTe by demonstrating a crossover from relativistic magnetization in low fields to non-relativistic magnetization in high fields.

Figure 1. The 180° periodicity of magnetization oscillations in low fields, which is characteristic of ferromagnets, is replaced by 90° periodicity in high fields, with the interplay between the minima and maxima at intermediate values of magnetic fields.

Publication: Orlova, N.N. Crossover from Relativistic to Non-relativistic Net Magnetization for MnTe Altermagnet Candidate / N.N. Orlova, A.A. Avakyants, A.V. Timonina, N.N. Kolesnikov, E.V. Deviatov // JETP Letters. – 2024. – Vol. 120. – DOI:10.1134/S0021364024602926

RSF project no. 24-22-00060

Physical Sciences, branch 1.3.2.3. “Physics of Magnetic Phenomena, Magnetic Materials and Structures, Spintronics”

Superdispersive plasmonic metamaterial

V.M. Muravev, K.R. Dzhikirba, M.S. Sokolova, A.S. Astrakhantseva, I.V. Kukushkin

Metamaterials are a class of artificial materials with unique electrodynamic properties that cannot be found in nature. In this work, we implemented a simple technology for assembling a 3D metamaterial consisting of stacked planar silicon chips with a metallic mesh lithographically fabricated on the chip surface (Fig. a). Therefore, a uniform metamaterial was created that acts as 3D plasma in the terahertz frequency range (0.1 – 1 THz). It was experimentally shown that the electrodynamic response of the metamaterial could be described in terms of the effective permittivity of plasma. Fabry–Pérot resonance spectroscopy was used to measure accurately the dispersion of the metamaterial in the terahertz frequency range. For large mesh periods, the dispersion of the electromagnetic wave passing through the metamaterial closely followed the plasmonic dependence, with the plasma frequency determined by the geometric parameters of the mesh and the chip thickness. In the other limit, when the mesh period was small, a new electrodynamic effect of the interaction between plasmonic and photonic modes arose. In this mode, the effective permeability of the metamaterial demonstrated extreme sensitivity to the THz radiation frequency – superdispersion. The discovered superdispersive property may have applications in spectroscopy and multiplexing.

Figure. (a) Photograph of one of the samples of the fabricated plasmonic metamaterial with a metallic mesh with a period of 0.3 mm and a strip width of 30 μm. (b) Transmission of nine silicon chips without a mesh (blue dots) and those with a metallic mesh (red dots). The low-frequency region of plasma opacity and the plasma edge (arrow) at a frequency of 146 GHz are clearly visible.

Publication: Muravev, V.M. Superdispersive plasmonic metamaterial / V.M. Muravev, K.R. Dzhikirba, M.S. Sokolova, A.S. Astrakhantseva, I.V. Kukushkin // Physical Review Applied. – 2024. – Vol. 21, Iss. 3. – P. 34041. – DOI:10.1103/PhysRevApplied.21.034041

RSF project no. 19-72-30003

Physical Sciences, branch 1.3.5.6. “New Optical Materials, Optical Photonics Components, Integrated Optics, Holography, Nanophotonics, Metamaterials, and Metasurfaces”

Development of methods of superconducting sigma neuron design

A.S. Ionin, L.N. Karelina, N.S. Shuravin, F.A. Razorenov, M.S. Sidel’nikov, S.V. Egorov, V.V. Bol’ginov

Figure 1. Proposed modification of the SN design implemented in 2023. Dashed lines show the proposed extension of the XJ region, and arrows illustrate the change in the position of the Josephson junctions of the SQUID.

The problems of designing superconducting sigma neurons (SN), which are a single interferometer with a shunt inductance, were considered. The prototype of the device was implemented in the Laboratory of Superconductivity, ISSP RAS, in 2023 in the form of a multilayer thin-film structure over a thick superconducting screen, as demonstrated in the figure. The experiment showed that the superconducting screen did not provide complete independence of the SN elements, as assumed in the initial model.

To improve the characteristics of the device, numerical calculation of the inductance matrix (IM) of SN in the proposed design was carried out, and a method for calculation of the transfer function (TF) was generalized to the case of an arbitrary IM. The calculation of the IM revealed asymmetry of the input signal in the SN circuits with identical geometry of receiving sections, direct interaction between the input and readout elements, and other parasitic interactions expressed by non-zero off-diagonal IM components. The distribution of superconducting currents in the SN prototype was presented, which took into account the real 3D geometry of the sample. It confirmed the mechanism of transfer of the input signal to the receiving circuit through ring superconducting currents in the screen. The generalization of the TF calculation method to the case of an arbitrary IM gave a parametric expression for the TF taking into account all IM components and simple quantitative conditions of compliance with the target TF shape. It was shown that taking into account the interaction between the SN and the measuring circuit led to renormalization of the output inductance, and the interaction between the input and readout elements led to an effective imbalance of the receiving elements of the SN. Prospective methods for improving the design to achieve the target shape of the TF were discussed.

Based on the results obtained, a method of modifying the design of the SN to improve its characteristics was proposed. In Fig. 1, the dashed lines show the proposed extension of the “Josephson” arm XJ, and the arrows illustrate the change in the position of the Josephson junctions of the SQUID.

Publications:

1. Ionin, A.S. Numerical simulation of the superconducting sigma neuron design / A.S. Ionin, S.V. Egorov, M.S. Sidelnikov, L.N. Karelina, N.S. Shuravin, M.M. Khapaev, V.V. Bolginov // Physics of the Solid State. – 2024. – Vol. 66, Iss. 7. – P. 987–993. – DOI:10.61011/PSS.2024.07.58963.25HH
2. Shuravin, N.S. Generalized Model of the Superconducting Sigma Neuron / N.S. Shuravin, L.N. Karelina, A.S. Ionin, F.A. Razorenov, M.S. Sidel’nikov, S.V. Egorov, V.V. Bol’ginov // JETP Letters. – 2024. – Vol. 120, Iss. 11. – P. 829–836. – DOI:10.1134/S0021364024603427

RSF project no. 23-72-00053

Physical Sciences, branch 1.3.2.8. “Quantum Macrophysics, Bose-Einstein Condensates, Superconductivity”

Anode-supported solid oxide fuel cell stack

I.N. Burmistrov, E.A. Agarkova, A.U. Sharafutdinov, D.V. Yalovenko, S.I. Bredikhin

For the first time in Russia, a kilowatt-class anode-supported solid oxide fuel cell (SOFC) stack was developed and manufactured (Fig. 1, left). Studies of the electrochemical characteristics of the stack confirmed its successful operation not only on pure hydrogen but also when using carbon-containing fuel, which imitates the result of steam reforming of natural gas (Fig. 1, right). With a small volume (1 l) and weight (5.4 kg) for SOFC stacks, the power obtained in the stack met the design values and was about 800 W. That made it possible to achieve high specific characteristics during operation on both pure hydrogen (830 W/l and 153 W/kg) and carbon-containing fuel (740 W/l and 136 W/kg) with an electrical efficiency of up to 48 %. The anode-supported SOFC stack developed at ISSP RAS is the basic element of high-efficient energy of the future and will lay the foundation for the development of SOFC power plants for various applications both at ISSP RAS and in other Russian scientific organizations and engineering bureaus.

Figure 1. A stack of 24 anode-supported SOFCs (left) and its electrochemical characteristics depending on the composition of the fuel mixture (right).

The result was obtained during the work under the research and development agreement No. 1284-21 “Optimization of the power and weight-and-dimensional characteristics of solid oxide fuel cell stacks for high-efficient transport and stationary power plants” dated March 01, 2021.

Chemical Sciences, branch 1.4.4.2. “Scientific Basis for Fuel Cells”

Experimental study of a large stable anticyclone in rotating turbulence

D.D. Tumachev, A.A. Levchenko, S.V. Filatov et al.

An unusual turbulent regime in rotating water has been experimentally studied for the first time. This regime is a stable anticyclone (Fig. 1), which is a vortex rotating in a direction opposite to the rotation of the setup. The vortex exists significantly longer than the Ekman time, which is the characteristic time of dissipation. The regime is non-standard for turbulence in rotating systems since cyclones are more stable structures than anticyclones due to cyclone-anticyclone asymmetry. There is a region of a mean cyclonic flow around the anticyclone, which is characterized by a significant degree of three-dimensionality judging by the chaotically moving vortices with different signs of vorticity and by the field of divergence that characterizes vertical velocity gradients according to the continuity equation. This regime is observed at cube rotation frequencies from 2.7 to 5.4 rpm and is characterized by the Rossby numbers from 0.52 to 0.3. These numbers indicate that large-scale velocities are subject to the Coriolis force. The Reynolds number is approximately 2000 for all experiments, indicating significant turbulence in the regime.

A model has been proposed, according to which the anticyclonic flow is supported by the absorption of inertial waves that propagate towards the vortex axis from the peripheral region and carry an anticyclonic angular momentum. A wave with a fixed frequency, wave number along the vertical, and axial number is absorbed at a certain distance from the vortex axis in the critical layer. On the contrary, waves that carry a cyclonic angular momentum are reflected and, hence, do not transfer their angular momentum to the anticyclone.

Figure 1. Distribution of vorticity over space for the regime with a large anticyclone in the center of the cube. The cube rotation frequencies are 3.6, 6.8, and 10.8 rpm. The cube rotates counterclockwise.

Publication: Tumachev, D.D. Observation of a large stable anticyclone in rotating turbulence / D.D. Tumachev, A.A. Levchenko, S.S. Vergeles, S.V. Filatov // Physics of Fluids. – 2024. – Vol. 36, Iss. 12. – P. 126620. – DOI:10.1063/5.0242193

State task of ISSP RAS: “Coherent States, Dynamics, and Phase Transitions in Liquids and Solids”, no. 122040600126-6 Physical Sciences, branch 1.3.6.3. “Physics of Nonlinear Waves and Nonlinear Dynamics”

Direct observation of pinning of Abrikosov vortices in a spatially inhomogeneous crystal EuRbFe₄As₄

M.S. Sidelnikov, A.V. Palnichenko, I.I. Zverkova, L.S. Uspenskaya, L.Ya. Vinnikov

Abrikosov vortex lattice on the inhomogeneous EuRbFe₄As₄ crystal at TD ≈ 18 K and H = 7.3 Oe.

A method of low-temperature decoration with ferromagnetic nanoparticles was used to study the ordering of Abrikosov vortices in the crystal of magnetic iron-based superconductor (IBS) EuRbFe₄As₄ with an admixture of non-superconducting phase EuRbFe₂As₂ with twin boundaries. The growth of EuRbFe₄As₄ single crystals by the self-flux method was accompanied by the formation of a secondary competing phase EuRbFe₂As₂. The effect of the secondary phase on the pinning of Abrikosov vortices in EuRbFe₄As₄ is of great practical interest since iron-based superconductors are viewed as materials for superconducting solenoids with a high critical field. Previously, the effect of the EuFe2As2 phase was considered only in the case of point inclusions, which are pinning centers.

The experiments were performed on a sample of a ≈ 15 μm-thick quasi-epitaxial film of the superconducting EuRbFe₄As₄ phase on a substrate of the non-superconducting parent phase with twinning. A linear ordering of Abrikosov vortices, which is not typical for iron-based superconductors, was observed for the first time. The direction of the chains coincided with that of the twin boundaries of the EuRbFe₂As₂ phase, and the distance between the chains corresponded to that between the twin boundaries. This ordering of the vortices can be explained by pinning in the mechanically stressed regions of the superconducting phase above the twin boundaries in the secondary phase-substrate. The pinning potential was estimated. The observed ordering of the vortices above the twin boundaries can be considered as one of the methods to control the vortex structure, which is promising for technical applications.

Publication:

1. Sidelnikov, M.S. Direct Observation of Pinning of Abrikosov Vortices in a Specially Inhomogenious Crystal EuRbFe₄As₄ / M.S. Sidelnikov, A.V. Palnichenko, K.S. Pervakov, V.A. Vlasenko, I.I. Zverkova, L.S. Uspenskaya, V.M. Pudalov, and L.Ya. Vinnikov // JETP Letters. – 2024. – Vol. 119, No. 7. – pp. 523–528. – DOI: 10.1134/S0021364024600514
2. Erratum DOI: 10.1134/S0021364024010016

RSF project no. 23-12-00307

Physical Sciences, branches
1.3.2.3. “Physics of Magnetic Phenomena, Magnetic Materials and Structures, Spintronics”
1.3.2.8. “Quantum Macrophysics, Bose-Einstein Condensates, Superconductivity”

The topological soliton in Peierls semimetal Sb

S.V. Chekmazov, A.S. Ksenz, A.M. Ionov, A.A. Mazilkin, A.A. Smirnov, E.A. Pershina, I.A. Ryzhkin, S.I. Bozhko et al.

Metal–insulator phase transitions are one of the basic phenomena that determine the properties of materials. Sb is Peierls semimetal. The crystal structure and energy spectrum of Sb are largely determined by the Peierls metal–insulator transition. A distinctive feature of the Sb crystal structure is the alternation of covalent and van der Waals bonds between (111) atomic planes. The energy gain related to the Peierls transition is due to covalent bonding. Violation of the Peierls conditions by dangling covalent bonds can be realized on the (111) surface of the Sb single crystal. By using the density functional theory (DFT), model calculations were carried out for the crystal structure and electron spectrum of model structures with a thickness of 41 monolayers (there were covalent dangling bonds on the surface) and 42 monolayers (there were van der Waals dangling bonds on the surface). Structural optimization of the Sb (111) surface containing covalent dangling bonds revealed the formation of a topological soliton centered at about 25 Å below the surface (marked by the arrow in Fig. (a)). The soliton was the violation of the alternation of short covalent and long van der Waals bonds between Sb (111) atomic layers in the bulk. This strong deformation of the crystal lattice resulted in the formation of electronic states associated with the soliton (Fig. (b)). The interaction between the TS and the electrons of the surface states led to a shift in the levels of the surface electronic states (Figs. (e) and (d)). At the soliton core, an increase in the electronic state density at the Fermi level by an order of magnitude was observed (Fig. (c)), which demonstrated an oscillating dependency in the soliton region.

The presence of solitons in real Sb crystals was confirmed experimentally. Monolayer steps were found on the cleaved Sb (111) surface by STM, showing that the surface contained different regions cleaved by van der Waals and covalent bonds. Tunneling spectra calculated using DFT and measured on both sides of the step were in agreement.

One of the most significant findings is the abnormally high density of electronic states at the Fermi level in the soliton region, which may lead to superconductivity in the soliton region at high temperatures.

Publication: Chekmazov, S.V. The topological soliton in Peierls semimetal Sb / S.V. Chekmazov, A.S. Ksenz, A.M. Ionov, A.A. Mazilkin, A.A. Smirnov, E.A. Pershina, I.A. Ryzhkin, O.Yu. Vilkov, B. Walls, K. Zhussupbekov, I.V. Shvets, S.I. Bozhko // Scientific Reports. – 2024. – Vol. 14. – P. 2331. – DOI:10.1038/s41598-024-52411-x

State task of ISSP RAS: “Physics, Technology, and Engineering of Defects in Materials for Alternative Energy Sources, Photovoltaics, and Sensorics”, no. 122040600124-2 Physical Sciences, branch 1.3.2.6. “Physics of Surfaces, Interfaces, and Other Extended Defects”