Dirac fermions emerging on the surface of the topological insulators, known for their spin-momentum locked and topologically protected states, are attractive for spintronics applications. The proximity of topological insulators to superlattices or molecular networks is expected to enhance the electronic correlations, a highly demanding task that yet remains challenging to achieve. Here we report on the successful syntheses of large-scale vdW-epitaxial C60 fullerene monomolecular layer on top of the topological insulator Bi2Te3 and establish the molecular superlattice formation by scanning tunneling microscopy observations. We discover the overlapping of Dirac fermions and massive molecular bands in the electronic spectrum, an intriguing effect, that has not been widely investigated. Furthermore, we show that adatom doping effectively tunes the Fermi level and molecular bands, enhancing this overlapping. Our results demonstrate the C60/Bi2Te3 interface as a versatile platform for exploring the physics of correlated fermions and non-trivial band topology.

Scaling the electronic and magnetic phases to the monolayer limit is able to produce a rich and complex landscape of emergent effects, highly promising for applications in ultracompact spintronic devices. Here, we report on the epitaxial synthesis of a two-dimensional Pb-based kagome monolayer HoPb 3 and suggest a strategy to engineer the periodic structure with alternating HoPb 3 and Pb stripes. Both phases demonstrate a Rashba-like spin polarization and several Van Hove singularities in the band structure, including high-order ones, which potentially may enable the strong electronic correlations. The DFT calculations have predicted that both 2D and quasi-1D phases exhibit an unusual combination of in-plane noncollinear antiferromagnetic alignment of Ho magnetic moments, along with small out-of-plane spin polarization, which makes them ferrimagnets. Furthermore, the striped phase was found to hold the fingerprints of the 1D Tomonaga-Luttinger liquid. Our results offer a versatile approach to control the anisotropy of low-dimensional materials, facilitating the development of tunable spintronic devices.

Discovery of superconductivity in the low-dimensional structures has become a frontier in the modern material science due to the prospective technological applications. Here we report on the epitaxial synthesis of a specific quasi-1D Tl-Ga alloy on the Si(111) surface, which is the Rashba metal with band structure displaying mixed 1D/2D character and demonstrating the superconductivity with a critical temperature slightly less than 2 K. The synthesis is supplemented by extensive studies of its atomic and electronic properties by scanning tunneling microscopy, low-energy electron diffraction, in situ transport measurements, and comprehensive density functional theory calculations. We investigated the interplay between the Tl-Ga alloy composition and resulting atomic-scale ordered phases. The discovered superconducting phase could find application in modern electronic devices and stimulate further efforts to engineer the thinnest superconductors.

Electronic correlations in two-dimensional (2D) systems are strongly governed by Van Hove singularities, which generate divergences in the density of states and enhance correlation effects. Although high-order Van Hove singularities (HOVHSs) are typically associated with engineered band structures that require external tuning, their intrinsic emergence in realistic crystalline materials remains largely unexplored. We report on an interface-driven mechanism that intrinsically stabilizes a type-II HOVHS (emerged at nonregular points of the Brillouin zone) in an atomically thin Pb monolayer epitaxially grown on Si(111). Combining angle-resolved photoemission spectroscopy, scanning tunneling spectroscopy, and state-of-the-art ab initio calculations, we demonstrated that the HOVHS forms in close proximity to the Fermi level within Rashba-split surface states and produces a pronounced power-law divergence of the density of states exceeding that of conventional saddle points. We show that HOVHS arises without any external control and is stabilized by strong spin-orbit coupling and orbital hybridization at the Pb/Si interface. Our results establish an interface-driven mechanism for generating HOVHSs in spin-orbit coupled two-dimensional superconductors.

Electronic correlations in two-dimensional (2D) systems are strongly governed by Van Hove singularities, which generate divergences in the density of states and enhance correlation effects. Although high-order Van Hove singularities (HOVHSs) are typically associated with engineered band structures that require external tuning, their intrinsic emergence in realistic crystalline materials remains largely unexplored. We report on an interface-driven mechanism that intrinsically stabilizes a type-II HOVHS (emerged at nonregular points of the Brillouin zone) in an atomically thin Pb monolayer epitaxially grown on Si(111). Combining angle-resolved photoemission spectroscopy, scanning tunneling spectroscopy, and state-of-the-art ab initio calculations, we demonstrated that the HOVHS forms in close proximity to the Fermi level within Rashba-split surface states and produces a pronounced power-law divergence of the density of states exceeding that of conventional saddle points. We show that HOVHS arises without any external control and is stabilized by strong spin-orbit coupling and orbital hybridization at the Pb/Si interface. Our results establish an interface-driven mechanism for generating HOVHSs in spin-orbit coupled two-dimensional superconductors.

Kagome materials serve as a versatile platform where an interplay of flat bands, Dirac Fermions, and Van Hove singularities enables the emergence of exotic strongly correlated phenomena. Recently, it was predicted that an ideal single layer kagome lattice may host high-order Van Hove singularities (HOVHSs) characterized by extremely flat dispersions, leading to drastic changes in electronic behavior. However, experimentally, HOVHSs have been observed up to now only in a narrow range of materials, mostly in graphene layers, but not in metal-semiconductor interfaces. Here, we report the discovery of HOVHSs in the monolayer-thick kagome metal LaTl3 epitaxially synthesized on the Si(111) substrate. The scanning tunneling microscopy observations and ab initio calculations indicate the kagome-like ordering of the LaTl3 layer, while the angle-resolved photoemission spectroscopy measurements and theoretical predictions uncover a rich and complex landscape of various Van Hove singularities emerged in the system, including high-order ones, which can significantly affect the anomalous Hall response and enable the unique high electron-correlation regime in the system. The discovered properties make the LaTl3 kagome monolayer a highly attractive material for ultracompact nanoelectronic devices.

We describe the Ruijsenaars' action-angle duality in classical many-body integrable systems through the spectral duality transformation relating the classical spin chains and Gaudin models. For this purpose, the Lax matrices of many-body systems are represented in the multi-pole (Gaudin-like) form by introducing a fictitious spectral parameter. This form of Lax matrices is also interpreted as classical-classical version of quantum-classical duality.

Integration of fullerene molecules into ultimately thin films gives rise to various fascinating effects, such as superconductivity, topology and quantum transport, however, strong substrate-mediated interaction in many hybrid molecular systems often suppresses the emergent electronic effects. In the present work, we interfaced the C60 fullerene molecular film and a 3D topological insulator Bi2Se3 and investigated the ordering and electronic properties of the system using various experimental techniques combined with the state-of-the-art first-principles calculations. We synthesized the highly-ordered epitaxial fullerene monolayer and found it to be electronically decoupled from the substrate, due to the negligible molecule-substrate interaction, which brings it to the nearly free-standing state. We showed that electron doping and atomic intercalation enrich its functionalities, since they boost carrier concentration and effectively shift the Fermi level to the vicinity of molecular flat bands, which may enable the high-electron correlation regime and reveal a great potential of C60/Bi2Se3 interface, as an advanced hybrid molecular 2D material.

Thallium (Tl) deposition onto the Au/Si(111)5 × 2 reconstruction followed by annealing at about 300 °C has been found to result in the formation of the surface structure having 4 × 2 periodicity. Similar to the most reconstructions in the (Au, Tl)/Si(111) system, Au and Tl do not intermix uniformly. While Au chains preserve their inner structure, Tl atoms being highly mobile at room temperature continuously migrate over the Si chains. Thallium donates electrons into the surface, that results in the two consequences: (i) filling the originally partially filled surface-state band, thus converting the metallic surface into an insulating state; (ii) transforming Si chains, which separate Au atomic rows, from the honeycomb-like to the zigzag according to the electron counting rule. The latter alters the inter-chain distance within the array of Au atomic wires. Au and/or Si chains contain point defects, which are masqueraded by the mobile Tl atoms producing peculiar “wavy” STM images.

The studies of electronic effects in reduced dimensionality have become a frontier in nanoscience due to exotic and highly tunable character of quantum phenomena. Recently, a new class of 2D ultrathin Ln$X_2$ metalloxenes composed of a triangular lattice of lanthanide ions (Ln) coupled with 2D-Xenes of silicene or germanene ($X_2$) was introduced and studied with a particular focus on magnetic and transport properties. However, the electronic properties of metalloxenes and their effective functionalization remain mainly unexplored. Here, using a number of experimental and theoretical techniques, we trace the evolution of electronic properties and magnetic ground state of metalloxenes triggered by external perturbations. We demonstrate that the band structure of Ln$X_2$ films can be uniquely modified by controlling the Xenes stacking, thickness, varying the rare-earth and host elements, and applying an external electric field. Our findings suggest new pathways to manipulate the electronic properties of 2D rare-earth magnets that can be adjusted for spintronics applications.

Using scanning tunneling microscopy and low-energy electron diffraction observations accompanied with the density-functional theory calculations, adsorption of Cr atoms onto the Si(111)4×1-In surface and its effect on the 4×1-to-8×2 structural transition were investigated. It was found that in contrast to other metal adsorbates, such as Na, In and Pb, which remain adatoms, Cr atom becomes embedded below the level of In atoms constituting the In nanowire. But in other respects Cr produces effects similar to those of other metals, namely it also induces distortion in the In rows of its residence resulting in doubling of the periodicity along the rows and also reduces the critical temperature of the 4×1-to-8×2 transition almost linearly with amount of deposited metal.

Lanthanide (Ln) elements Gd and Yb alloyed with a Pb monolayer on the Si(111) substrate form LnPb3 compounds having the same crystal structure. They comprise a single-atom-thick Pb layer arranged in a slightly distorted kagome lattice with Ln atoms filling the hexagonal voids. They have similar electronic band structures except for the Fermi level position, which varies between the divalent Yb- and trivalent Gd-containing compounds by ∼0.47 eV. The ability to create a 2D solid solution with the unified continuous Pb layer and hexagonal voids randomly filled with either Gd or Yb atoms allows precise control of the Fermi level position. Small alteration of the Fermi level triggers drastic changes in the Fermi surface topology due to the Lifshitz transition, hence in the physical properties. In particular, the sheet resistance of the GdxYb1-xPb3/Si(111) system can be controllably varied over an order of magnitude range.

A critical assessment and processing of experimental data published in the literature on the stability of hydroxide and chloride complexes of Au(I) was carried out. Based on the obtained Gibbs energies of AuOH(aq), AuCl(aq), and AuCl_2^ - , the standard thermodynamic properties and parameters of the Helgeson–Kirkham–Flowers model equation of state were determined for these species. The resulting set of parameters makes it possible to calculate the solubility of Au in chloride fluids up to 1000°C, 5000 bar with the possibility of extrapolation to higher PT parameters. As a geological application of the obtained data, a model calculation of the deposition of native gold by cooling chloride–sulfide fluid was carried out with an assessment of changes in the composition of the fluid, the sequence of formation of solid phases, and changes in the fineness of gold.

We consider the classical integrable (1+1) trigonometric gl_N Landau–Lifshitz models constructed by means of quantum R -matrices that also satisfy the associative Yang–Baxter equation. It is shown that a (1+1) field analogue of the trigonometric Calogero–Moser–Sutherland model is gauge equivalent to the Landau–Lifshitz model that arises from the Antonov–Hasegawa–Zabrodin trigonometric nonstandard R -matrix. The latter generalizes Cherednik’s 7 -vertex R -matrix in the GL_2 case to the case of GL_N . An explicit change of variables between the (1+1) models is obtained.

Elucidating how changing of the dimensionality affects the property of the matter is the key challenge problem of the nanoscience. In particular, it has recently been reported that 2D liquids have fundamentally different dynamic properties to 3D liquids. Herein, the ultimate physical limit is addressed, when the liquid is confined to a single‐atom layer. The case has been realized with the Tl–Pb alloy layer grown on Si(111) substrate terminated by a single‐layer . At room temperature, the alloy behaves as a system of the immiscible melted metals confined in a single‐atom layer. In the scanning tunneling microscopy observation, Tl and Pb arrays have different contrasts that allows a direct visualization of evolution of the forming structures within atomic layer, as a function of the time and layer composition. In particular, it has been found that the structures look much like the Turing patterns. The obtained experimental dataset, especially the recorded STM videos, is believed to provide a hint for the prospective theoretical understanding of the dynamics of the single‐atom‐thick liquids.

Magnetoresistance of the double-atomic-layer rect- 7 x 3-In/Si(111) phase was measured in situ using the four-point-probe technique in the temperature range from 2.5 to 33 K and magnetic fields from 8 to 8 T. The rect- 7 x 3-In/Si(111) was found to demonstrate a classical quadratic behavior of magnetoresistance at fields lower than 0.2 T, and a large positive linear magnetoresistance at fields up to 8 T in the low-temperature range of up to 10 K. In contrast, the results obtained on the parent single-and double-atomic In layers formed on the NiSi2/Si(111) substrate show much lower values of magnetoresistance. In view of the density functional theory calculation results, which reveal the presence of tiny Fermi pockets in the rect- 7 x 3-In/Si(111) electronic band structure, we attribute the observed large linear magnetoresistance at the low-temperature range to a quantum mechanical origin.

Experimental data available in the literature on the solubility of Cu (met.) and Cu2O (cuprite) in water under hydrothermal conditions have been processed. Key experiments on the solubility of cuprite were carried out at 300°C and the saturated vapor pressure of H2O vs. pH of the solution. As a result, a set of values of thermodynamic properties for 25°C, 1 bar and the parameters of the Helgeson–Kirkham–Flowers and Akinfiev–Diamond equations of state for Cu(I) hydroxocomplexes were obtained, which make it possible to describe their behavior in a wide range of temperatures (0–600°C), pressures (1–3000 bar), and densities of aqueous fluid (0.01–1 g/cm3). As has been shown by thermodynamic modeling, Cu+ ions are prevalent in the acidic and weakly alkaline regions of the aqueous solvent over the entire temperature and pressure range studied. The effect of the neutral CuOH hydroxocomplex begins to show up in the alkaline region at T > 300°C and grows with increasing temperature. The second copper hydroxocomplex Cu( OH)_2^ - shows up only in the strongly alkaline region, and the temperature has almost no effect on its behavior.

We study the GL_N rational R -matrix, which turns into the 11 -vertex R -matrix in the N=2 case. First, we describe its relations to dynamical and semidynamical R -matrices using the IRF– vertex type transformations. As a by-product, a new explicit form of the GL_N R -matrix is derived. Next, we prove the quantum and the associative Yang–Baxter equations. A set of other R -matrix properties and R -matrix identities are also proved.

An investigation is performed of planar memristive structures to validate the choice of their basic materials, study their functional properties, and determine and develop the structure the resistive switching mechanism. Mesoscopic heterostructures based on epitaxial 〈001〉 oriented films of high-temperature superconductor YBa2Cu3O7 − δ and doped manganite La1 − xSrxMnO3 − δ, are obtained, and the properties of the percolation channels of structures based on these compounds are studied. Self-adaptive electroforming effects in microcontact heterostructures based on epitaxial manganite films are studied. Numerical calculations using the critical electric field model show there is self-electroformation in strong electric fields, and a gap structure that provides resistive switching reproducibility forms in the zone of contact.

Submonolayer Bi film grown on the InAs(111)A surface demonstrates quasi-1D and Rashba spin-polarized states characterizing the system as an advanced spintronics material fabricated in the ultimate 2D limit.