# Andrey M. Tokmachev's research while affiliated with Kurchatov Institute and other places

## Publications (61)

Article
2D magnetic materials are at the forefront of research on fundamentals of magnetism; they exhibit unconventional phases and properties controlled by external stimuli. 2D magnets offer a solution to the problem of miniaturization of spintronic devices. A technological target of materials science is to find suitable magnetic materials and scale their...
Article
Two-dimensional (2D) magnetic materials promise unconventional properties and quantum phases as well as advances in ultra-compact spintronics. Miniaturization of 2D magnets often reaches a single monolayer but in general can go beyond this limit, as demonstrated by 2D magnetism of submonolayer Eu superstructures coupled with Si. The question is whe...
Chapter
Magnetism is emerging as a key property of two-dimensional (2D) materials and heterostructures. 2D magnetism engenders new quantum and topological phases, endows materials with unexpected functionalities, and inspires new device concepts. The family of Xenes and their derivatives—materials at the core of 2D research—present an important constituent...
Article
Integration of oxides with semiconductor substrates merges functional properties of the two material systems. Significant progress has been made in controlled synthesis of crystalline oxides on silicon. Other semiconductors, such as germanium, are however lagging behind but would benefit from the range of functionalities provided by oxides. Here, w...
Article
The rank and signature of the linear transformation between the reactant and product unit cells are utilized to classify solid-state reactions. The classification is applicable to topotaxy and reactive epitaxy....
Article
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Integration of oxides with silicon fuses advanced functional properties with a mature technological platform. In particular, direct EuO/Si contact holds high promise for spintronics but requires single‐crystalline epitaxial films with atomically sharp interfaces. The standard approach employing regular 2D superstructures of metal atoms on the Si su...
Article
2D magnets hold high promise for unconventional quantum phases, exploration of fundamental physics of magnetism, ultra-compact devices based on van der Waals heterostructures. Graphene is a constant inspiration for design of 2D materials; stoichiometric graphene-based compounds with magnetic atoms give rise to 2D ferromagnets. Unfortunately, additi...
Article
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Integration of crystalline oxides with silicon provides a versatile platform to extend and advance silicon technology. The interface between oxide and Si controls the structure and functional properties of the resulting material. In particular, the formation of a submonolayer metal phase on silicon is the standard approach to stabilize the epitaxia...
Article
Recent discoveries of intrinsic 2D magnets open up vast opportunities to address fundamental problems in condensed matter physics, giving rise to applications from ultra-compact spintronics to quantum computing. The ever-growing material landscape of 2D magnets lacks, however, carbon-based systems, prominent in other areas of 2D research. Magnetiza...
Article
Design of materials with special properties benefits from establishing deep structural and electronic analogies between emerging and existing materials. The Zintl anion [Al 2 Si 2 ] 2– is both isostructural and isoelectronic to bilayer...
Article
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The concept of dimensionality is fundamental in physics, chemistry, materials science, etc. Low-dimensional and layered materials are distinguished by their unique physical properties and applications. Concurrently, low-dimensional reactants, products, and reaction spaces extend the toolbox of materials science considerably. Here, the concept of di...
Article
2D magnets have recently developed into a class of stoichiometric materials with prospective applications in ultra-compact spintronics and quantum computing. Their functionality is particularly rich when different magnetic orders are competing in the same material. Metalloxenes REX2, silicene or germanene-heavy counterparts of graphene-coupled with...
Article
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Buckled elemental analogs of graphene—2D‐Xenes silicene, germanene, and stanene—and their derivatives are predicted to host high‐mobility carriers. Experiments, however, have not as yet confirmed the predictions. Here, high‐mobility (exceeding 10⁴ cm² V⁻¹ s⁻¹) carriers are discovered in intercalated multilayer germanene. Epitaxial films of antiferr...
Article
Intrinsic functionality of 2D materials is crucial for both fundamental studies and practical applications. In particular, 2D magnetism has recently emerged as a major research field bringing in new concepts, physical effects, and device designs. However, the list of stoichiometric 2D magnets is still rather short and would benefit from extension b...
Article
Recent discoveries of intrinsic two-dimensional ferromagnetism in layered compounds drive intense research on their fundamental properties and spintronic applications in atomically thin materials. In these materials, ferromagnetism engenders remarkable transport and optical phenomena and can be controlled electrically. However, coupling of carriers...
Article
Ferromagnetic insulators are widely employed to induce magnetic phenomena in adjacent layers via proximity effect. This approach could make non-magnetic materials (ranging from silicon to graphene) available for spintronic applications. Eu chalcogenides, EuO in particular, are highly efficient spin generators but suffer from low Curie temperatures....
Article
As the thickness of layered compounds approaches the monolayer limit, new electronic states and properties emerge. The sheer range of such properties is astounding but the list did not include intrinsic magnetism. Until recently. At the moment, several compounds do reveal intrinsic ferromagnetism at the 2D limit. However, they seem to be chemically...
Article
The mature silicon technological platform is actively explored for spintronic applications. Metal silicides are an integral part of the Si technology used as interconnects, gate electrodes, diffusion barriers; their epitaxial integration with Si results in premier contacts. Recent studies highlight the exceptional role of electronic discontinuities...
Article
Antiferromagnetic spintronics is actively explored for use in data storage to enhance robustness, switching speed and packing. A number of archetypal antiferromagnets formed by d-electron (transition) metals are traditionally employed in studies of spin dynamics and control. In contrast, rare-earth antiferromagnets exhibiting 4f-electron magnetism...
Article
Addition of magnetism to spectacular properties of graphene may lead to novel topological states and design of spin logic devices enjoying low power consumption. A significant progress is made in defect-induced magnetism in graphene – selective elimination of pz orbitals (by vacancies or adatoms) at triangular sublattices tailors graphene magnetism...
Article
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The appeal of ultra-compact spintronics drives intense research on magnetism in low-dimensional materials. Recent years have witnessed remarkable progress in engineering two-dimensional (2D) magnetism via defects, edges, adatoms, and magnetic proximity. However, intrinsic 2D ferromagnetism remained elusive until recent discovery of out-of-plane mag...
Article
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Superconductivity and ferromagnetism in a number of uranium-based materials come from the same f-electrons with a relatively large effective mass, suggesting the presence of a band of heavy quasiparticles, whose nature is still a mystery. Here, UGe2 dynamics in both ferromagnetic and paramagnetic phases is studied employing high-field μ⁺SR spectros...
Article
Facing physical limits to further development, modern electronics explores alternative approaches. One of the most promising routes is offered by spintronics employing spin degree of freedom. Silicon spintronics is especially important due to the central technological role of Si. This technology requires non-equilibrium spin polarization in non-mag...
Article
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Silicene, a Si-based analogue of graphene, is predicted to exhibit topological electronic phases with exotic properties capable to revolutionize electronics. In particular, the silicene structure is highly advantageous for spintronics. However, lack of synthetic routes to free-standing and magnetically functionalized silicene compounds prevents exp...
Article
Silicene, a Si analogue of graphene, is suggested to become a versatile material for nanoelectronics. Being coupled with magnetism, it is predicted to be particularly suitable for spintronic applications. However, experimental realization of free-standing silicene and its magnetic derivatives is lacking. Fortunately, magnetism can be induced into s...
Article
Epitaxial integration of oxides with the ubiquitous silicon technological platform promises devices with dreamed-of functionality but is difficult to achieve due to chemical processes at the Si/oxide interface. The standard approach suggests a protective template – a surface superstructure of SrSi2 stoichiometry; still, only a handful of oxides cou...
Article
Semiconductor spintronics provides a framework for hybrid devices combining logic, communication and storage, circumventing limitations of the current electronics, especially with respect to the energy efficiency. Enormous efforts have been invested worldwide into the development of spintronics based on Si, the mainstream semiconductor platform. No...
Article
Full-text available
High transverse magnetic field and zero field muon spin rotation and relaxation measurements have been carried out in a lightly oxygen-doped high-T c parent compound La 2 CuO 4 in a temperature range from 2 K to 300 K. As in the stoichiometric compound, muon spin rotation spectra reveal, along with the antiferromagnetic local field, the presence of...
Chapter
The diversity of the various forms of water stems from systems of hydrogen bonds. Cooperative behaviour of hydrogen-bond networks gives rise to unique properties of water systems. A number of approaches to understand and model the collective behaviour of hydrogen bonds and predict their properties on the basis of a small number of calculations have...
Article
Full-text available
Heavy fermion (HF) compounds are well known for their unique properties, such as narrow bandwidths, loss of coherence in a metal, non-Fermi-liquid behaviour, unconventional super-conductivity, huge magnetoresistance etc. While these materials have been known since the 1970s, there is still considerable uncertainty regarding the fundamental mechanis...
Article
Full-text available
Heavy fermion (HF) compounds are well known for their unique properties, such as narrow bandwidths, loss of coherence in a metal, non-Fermi-liquid behaviour, unconventional super-conductivity, huge magnetoresistance etc. While these materials have been known since the 1970s, there is still considerable uncertainty regarding the fundamental mechanis...
Article
Silicene, a 2D honeycomb lattice of Si atoms similar to graphene, is expected to be a platform for nanoelectronics and home to novel quantum phenomena. Unlike graphene, free-standing silicene is notoriously difficult to stabilize, while strong hybridization of silicene with substrates destroys its desirable properties. On the other hand, Dirac cone...
Article
Full-text available
High transverse magnetic field and zero field muon spin rotation and relaxation measurements have been carried out in a lightly oxygen-doped high-Tc parent compound La2CuO4 in a temperature range from 2 K to 300 K. As in the stoichiometric compound, muon spin rotation spectra reveal, along with the antiferromagnetic local field, the presence of an...
Article
Full-text available
Metal-silicon junctions are crucial to the operation of semiconductor devices: aggressive scaling demands low-resistive metallic terminals to replace high-doped silicon in transistors. It suggests an efficient charge injection through a low Schottky barrier between a metal and Si. Tremendous efforts invested into engineering metal-silicon junctions...
Article
Full-text available
Silicon spintronics requires injection of spin-polarized carriers into Si. An emerging approach is direct electrical injection from a ferromagnetic semiconductor - EuO being the prime choice. Functionality of the EuO/Si spin contact is determined by the interface band alignment. In particular, the band offset should fall within the 0.5-2 eV range....
Article
Full-text available
Control and manipulation of the spin of conduction electrons in industrial semiconductors such as silicon are suggested as an operating principle for a new generation of spintronic devices. Coherent injection of spin-polarized carriers into Si is a key to this novel technology. It is contingent on our ability to engineer flawless interfaces of Si w...
Article
The ferromagnetic semiconductor EuO is believed to be an effective spin injector when directly integrated with silicon (Si). Injection through spin-selective ohmic contact requires superb structural quality of the interface EuO/Si. A recent breakthrough in manufacturing free-of-buffer-layer EuO/Si junctions calls for structural studies of the inter...
Article
Full-text available
Ferromagnetic semiconductor europium monoxide (EuO) is believed to be an effective spin injector when directly integrated with silicon. Injection through spin-selective ohmic contact requires superb structural quality of the interface EuO/Si. Recent breakthrough in manufacturing free-of-buffer-layer EuO/Si junctions calls for structural studies of...
Article
Full-text available
The diversity of the various forms of water stems from systems of hydrogen bonds. Cooperative behaviour of hydrogen-bond networks gives rise to unique properties of water systems. A number of approaches to understand and model the collective behaviour of hydrogen bonds and predict their properties on the basis of a small number of calculations have...
Article
Geminals are counterparts of two-electron chemical bonds and lone pairs in the realm of wave functions. Antisymmetrized products of geminals provide a solid framework for studies of electron pairing in molecular systems. Natural advantages of geminal wave functions such as the correct description of bond breaking and formation make them a powerful...
Article
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Functional oxides demonstrate a wide range of magnetic, optical and transport properties. Their integration with silicon promises significant advances in electronics. An important key in enabling brand-new oxide technologies is the utilization of silicon/oxide epitaxy, thus making quality of the interface a critical issue. The progress depends on o...
Conference Paper
Full-text available
The origin of a pseudogap in the underdoped phase of cuprates has become one of the leading issues in understanding the mechanism(s) of high-Tc superconductivity. Several experiments (i.e. polarized neutron diffraction studies) support theoretical models based on the circulating current (CC) picture. These CC models suggest a novel ordered phase fo...
Article
Full-text available
Amato {\it et al.} have reported transverse field muon spin rotation experiments performed on single crystal of MnSi in a single magnetic field of 5200 Oe at a single temperature of 50 K. They present the angular dependence of the muon precession frequencies which they interpret in terms of dipolar magnetic field experienced by bare muons. Such int...
Article
Full-text available
Magnetic semiconductors are highly promising materials for spintronics. Among them europium (II) oxide makes a unique working host material due to a remarkable combination of magnetic and transport properties. Its electronic structure and various properties are often described in terms of spin polarons – local ferromagnetic clusters in the paramagn...
Article
Materials in which charge and spin degrees of freedom interact strongly offer applications known as spintronics. Following a remarkable success of metallic spintronics based on the giant-magnetoresistive effect, tremendous efforts have been invested into the less developed semiconductor spintronics, in particular, with the aim to produce three-term...
Data
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Article
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Muon spin rotation measurements supported by magnetization experiments have been carried out in a stoichiometric high-$T_c$ parent compound La$_2$CuO$_4$ in %the a temperature range from 2~K to 340~K and in transverse magnetic fields up to 5~T. Along with the antiferromagnetic local field, muon spin rotation spectra indicate presence of an addition...

## Citations

... The replacement of Si(001) with Ge(001) hits a sweet spot: The two surfaces are isostructural, and the chemistry of Si and Ge bears some similarities because the elements are neighbours in group 14 of the Periodic table; on the other hand, Si and Ge differ in the electronic structures and interatomic distances which may result in differences between magnetic properties of 2D silicides and germanides [8]. Eu forms a number of phases on Ge(001), not always the same as Eu on Si(001) [33]; it thus allows for both comparison of isostructural magnets and extension to new structural patterns. Together with Eu-on-Si, the Eu superstructures on Ge establish a class of subML magnets. ...
... In particular, low-temperature oxide growth on Si(001) is insensitive to the choice of metal reconstruction, whether the metal coverage is 1/2 ML or higher, as the synthesis proceeds via the same 1 Â 3 phase. 21 On the other hand, synthesis on bare, unprotected Si(001) is shown to result in oxide/Si heterostructures of better crystalline quality because of chemical reactions at the interface. 22 For synthesis on bare Ge(001), formation of GeO x constitutes an important problem. ...
... In the experiment, Tokmachev et al. observed that the sub-monolayer of Eu atoms selfassembled on the silicon surface exhibited an easyplane magnetism. 9 Similar easy-plane magnetisms were also detected in Eu/graphene, 10 Eu/silicene, 11 and Eu/germanene systems. 12 However, their T BKT are smaller than 20 K. [9][10][11][12] Pinto et al. demonstrated a BKT phase transition in monolayer CrCl 3 grown on graphene/6H-SiC(0001) substrate with T BKT of 12.95 K, 13 which is consistent with Lu' s prediction 14 . ...
... Electronic structure calculations of MAl 2 Si 2 suggest that the M atoms play a minor role in the metallic conductivity. 43,44 A similar conclusion has been drawn for EuCd 2 As 2 the charge transport is basically confined to anionic bilayers spaced by insulating magnetic layers of Eu. 40 On the other hand, the strong dependence of carrier mobilities on temperature (Figure 6b) suggests an important role of the AFM order. At high temperature, magnetic fluctuations provide an effective channel for both spin and momentum relaxation and disrupt the coherent transport. ...
... On the other hand, transition from 1 to 2 monolayers may bring significant changes to the magnetic structure [3,12,13]. In any case, the moments are smaller than those expected for fully spin-polarized Eu ions -element-selective studies of related 2D materials employing X-ray magnetic circular dichroism [33,34] identify a competition between FM and antiferromagnetic states as a possible reason. This complex magnetic structure would constitute an enormous challenge for any computational approach aiming at description of magnetism in Eu-intercalated FLG; the problem is aggravated by strong electron correlations characteristic to 4f systems, Eu compounds in particular. ...
... However, we can surmise the structures employing the analogy between Eu/Ge(001) and related systems. In particular, we can use information on Eu/Si(001) phases [38][39][40]. On the other hand, we can take advantage of the strong structural analogy between Eu and Sr compounds, arising from their very close ionic radii and bonding characteristics. ...
... The discovery of 2D van der Waals ferromagnets [3,4] has initiated a flurry of studies on fundamentals of magnetism and magnetic quantum phases with particular focus on spintronic applications [5]. The existing 2D materials support various magnetic structures, ferromagnetic [3,4,6], antiferromagnetic [4,7], and those formed by competing magnetic states [8][9][10]. 2D magnets range from metals [6] to insulators [3,4,11], even in chemically identical materials, depending on the number of monolayers (MLs) N [12]. ...
... 4,14 What is particularly fortunate is that a route to produce epitaxial films of EuAl 2 Si 2 on silicon has been devised recently. 30 Thus, this compound is an excellent candidate in a search for high carrier mobility in a magnetic layered nanomaterial. ...
... The synthesis requires a smooth pristine Ge(001) surface. We probed different approaches to remove the native oxide from Ge(001); the best quality of the surface comes from a combination of wet-etching by ammonia solution with subsequent heating of the substrate (see the Experimental Section), although other techniques to clean Ge(001) are also successfully applied [35]. The clean Ge(001) surface produces the well-known 2 × 1 reconstruction corresponding to formation of surface Ge-Ge dimers; a characteristic reflection highenergy electron diffraction (RHEED) image is given by Fig. S1(a) in the Electronic Supplementary Material (ESM). ...
... [17][18][19][21][22][23][24][25] The interest to EuO arises from its remarkable properties. It is a ferromagnetic semiconductor with record magneto-optical 26 and magnetotransport 27 characteristics. Its electronic structure and the resulting properties are tuned by doping 28 and strain engineering; 29 the latter makes EuO multiferroic. ...