A class of frustrated one-dimensional periodic Heisenberg spin systems formed either by triangular unit cells with spin 1/2 or by composite unit cells formed by two different structural units, triangles and small linear segments formed by an odd number of spin-1/2 is investigated. Based on perturbative processing and numerical calculations of the density matrix renormalization group method, the gapless

The nonlinear effect of the energy localization on topological inhomogeneities is investigated in the sine-Gordon systems. The regimes of nonlinear oscillations of nonequilibrium configurations of domain walls in the quasi-one-dimensional ferromagnet are described in terms of kink and breather solutions of the sine-Gordon equation. The conditions of the energy localization, i.e., the formation of breather

The thermodynamic properties of a one-dimensional spin-crossover molecular chain under constant external pressure are investigated. The effective compressible degenerate Ising model is used as a theoretical basis. Analytical results for the crossover from low to high spin are obtained using the transfer matrix formalism. Exact expressions are obtained for the fraction of molecules in the high-spin

Electrical transport properties of random binary networks composed of high-Tc superconductor Bi2Sr2Ca2Cu3O10+x (Bi2223) microparticles and half-metal ferromagnet La2/3Sr1/3MnO3 (LSMO) nanoparticles have been investigated. The experimental current-voltage characteristics of bulk samples of nanocomposites with a volumetric content of 4:1 components are well described by the Berezinsky–Kosterlitz–Thouless

This paper is devoted to the study of thermodynamics of the quasi-1D spin models with Ising interaction between complex unit cells by transfer-matrix method. The field and the temperature dependences of the main thermodynamic characteristics have been investigated. It is shown that the field dependence of the magnetization at low temperatures for the models of “comb” and “decorated comb,” and decorated

The effect of an external magnetic field on phase transitions, magnetic and thermodynamic properties of the antiferromagnetic Ising model on a body-centered cubic lattice with competing exchange interactions was studied using the replica algorithm of the Monte Carlo method. It is shown that a second-order phase transition is observed in the range of magnetic field values 7.0 ≤ H ≤ 10.0, and a first-order

The magnetic properties of thin-film multilayers [Fe/Py]/FeMn/Py are investigated as a function of temperature and thickness of the antiferromagnetic FeMn spacer using SQUID magnetometry. The observed behavior differs substantially for the structures with 6 nm and 15 nm FeMn spacers. While the 15 nm FeMn structure exhibits exchange pinning of both ferromagnetic layers in the entire measurement temperature

It was studied the electrical magnetoresistance of nickel-and boron-doped filamentary silicon crystals in which a metal-insulator transition is observed. A giant magnetoresistance reaches up to 280% in the Si whiskers with doping concentration of boron р300K = 5⋅1018 cm−3 in the magnetic fields with induction up to 14 T at temperature 4.2 K. Peculiarities of magnetoresistance at low temperatures were

The analytical model is constructed for the description of the spin wave propagation through a system consisting of two ferromagnets without and with the Dzyaloshinskii–Moriya interaction, separated by a flat interface. The dependences of transmission and reflection coefficients of spin wave are found as a function of Dzyaloshinskii-Moria constant which is known to be strongly temperature dependent

The frequencies of low-lying electronic excitations in the quasi-one-dimensional antiferromagnet CsFeCl3 · 2H2O were determined by Raman spectroscopy. The lowest of them (57 cm−1) was attributed to the magnon-like excitation of the chain of Ising spins of paramagnetic Fe2+ ions. And the next one (77 cm−1) can most likely be attributed to the exciton-like one, associated with the electronic transition

Schrodinger equation for system of two mobile spinless nucleus with Z0 = 2 and four electrons (4He2-dimer) has been solved in the framework of exact diagonalization approach. The spectrum has been obtained with basis of 1134 functions built as direct product of one-particle hydrogen-like functions which are solutions of the exactly solved Sturm-Liouville problem. The asymptotic (Van der Waals) behavior

The most significant experimental results and theoretical concepts related to chromium dioxide-based composites, according to their influence on the evolution of modern understanding of electron transport phenomena in disordered magnetic systems, are presented. It is shown that the variety of physical processes taking place in powder materials does not allow the development of a holistic theoretical

The interaction between injected negative charges and vortex motion formed by standing waves with the frequency ω/2π = 49.88 Hz on the surface of normal and superfluid helium has been experimentally studied. It has been found that the vorticity generation results in the redistribution of the current at segments of a collector. A change in the trajectory of the motion of charges from a source to a receiving

Some unique properties of superconducting devices are promising for the development of modern quantum technologies. Superconducting quantum circuits use large coupling constants and provide good scalability and controllability due to their macroscopic dimensions. Still, micro-fabrication methods have some hardship with reproducibility of identical superconducting quantum circuits. The dressed state

The work investigated the effect of high hydrostatic pressure up to 12 kbar on the fluctuation conductivity of medium-doped praseodymium ( x ≈ 0.23 ) single-crystal Y1−xPrxBa2Cu3O7−δ samples. It was found that in contrast to the pure YBa2Cu3O7−δ samples and the Y0.95Pr0.05Ba2Cu3O7−δ samples lightly doped with praseodymium, the application of high pressure leads to a significant decrease in the transverse

We carried out the analysis of the return current of dc SQUID based on tunnel Josephson junction with unconventional current-phase relation. We analyzed two cases of current-phase relation with additional terms to the first harmonic sin φ: a case of the second harmonic sin 2φ and the case of the fractional term sin (φ/2). It is shown that the changing of the return current of dc SQUID on junctions

The magnetic structures of the ground state, phase transitions, and the thermodynamic properties of a two-dimensional ferromagnetic Potts model with the number of spin states q = 4 on a kagome lattice are studied using the Wang-Landau algorithm of the Monte Carlo method, taking into account the interactions of the nearest and the next-nearest neighbors. The studies were carried out for the value of

The ground state behavior of the spinless fermion chain with an interaction between fermions at neighboring sites is studied for free open boundaries. For the strong enough repulsion boundary gapless states (bound state of Majorana operators from opposite sites of the chain) can exist inside the gap for bulk excitations, i.e., in the topological insulator regime. We propose to use those Majorana zero

The simple model that can describe structure and charge ordering in complex doped organic crystals is proposed. We consider the quasione-dimensional model of a crystal with chains (stacks) of flat BEDT-TTF molecules. In a chain of large molecules, small molecules fill every space between large molecules. The interaction between all molecules is described by the Lennard-Jones potential. It is shown

A quantum description of the surface waves in an isotropic elastic body without the use of the semiclassical quantization is proposed. The problem about the surface waves is formulated in the Lagrangian and Hamiltonian representations. Within the framework of the generalized Debye model, the contribution of the surface phonons (“rayleighons”) to thermodynamic functions is calculated. It is emphasized

The results of experimental investigations on the low-temperature fluorescence and absorption spectra of the 1- and 2-fluoronaphthalene impurities in the crystalline naphthalene are presented and analyzed. When the 1- and 2-fluoronaphthalene concentrations are less than 1%, the absorption and fluorescence spectra are shown to be composed of two identical band series, induced by the formation of two

The absorption spectra of RbCu2Cl3 and Rb2Cu3Cl5 thin films were studied in the 2−6 eV spectral and 90−450 K temperature ranges. The localization of excitons in CuCl 4 3 − structural elements of crystal lattice of compounds, three-dimensional nature of excitons in RbCu2Cl3 and two-dimensional nature of excitons in Rb2Cu3Cl5 were established. The exciton spectra of RbCu2Cl3 and Rb2Cu3Cl5 thin films

The Coulombic effect on microwave-induced electron heating in a 2D electron gas on liquid helium under quantizing magnetic field is theoretically studied. An extension of the linewidth of the intersubband resonance which takes into account squeezing of the electron density of states into Landau levels and strong internal electric fields of fluctuational origin is proposed. This approximation results

The escape rate of S → R switching (from superconducting S state to resistive R state) in Josephson junction formed by s-wave single-band (SB) and three-band (ThB) superconductors (SB/ThB junctions) in macroscopic quantum tunneling regime is investigated. We use the effective critical current approximation in SB/ThB junctions. It was shown that escape rate can exhibit qualitative features in the case

We considered a nanoelectromechanical system consisting of a movable Cooper-pair box qubit, which is subject to an electrostatic field, and coupled to the two bulk superconductors via tunneling processes. We suggest that qubit dynamics is related to that of a quantum oscillator and demonstrate that a bias voltage applied between superconductors generates states represented by the entanglement of qubit

Influence of the external electric field and the external strain on a quantum paramagnetic insulator is studied. It is shown that the external electric field and/or strain can cause drastic changes in the magnetic characteristics of the paramagnet.

The transmission coefficient T of the Dirac quasielectrons through a rectangular potential barrier in the α-T3 model is calculated and analyzed in the continuum approach. The dependence of the transmission rate on para-meter α, which characterizes the degree of coupling of the central atom with the atoms in the vertices of the hexagonal lattice, and parameter β, which is equal to the ratio of Fermi

The long-term stability of well-known TVO sensors before and after gamma irradiation was investigated during almost 17 years. Five of six sensors, calibrated in the temperature range from 3 to 300 K, were selected according to a requirement of their relative accuracy ΔT/T ≤ ± 0.25% at the cryogenic temperature range. Long-term stability measurements made 7.5 years after calibration are in good agreement

We calculate the extremal cross-sectional areas and cyclotron masses for the Fermi-surface pockets in Dirac and Weyl topological semimetals. The calculation is carried out for the most general form of the electron energy bands in the vicinity of the Weyl and Dirac points. Using the obtained formulas, one can find parameters characterizing the Dirac and Weyl electrons in the topological semimetals from

IR absorption spectra of 1-butanol isolated in an argon matrix were obtained at temperatures from 10 to 50 K. The conformational behavior of 1-butanol was analyzed using the results of quantum-chemical simulation of the structure and vibrational spectra of its small clusters. We studied the conformational composition of 1-butanol in matrix isolation and showed the transformation of its structure that

We employ low-temperature matrix-isolation FTIR spectroscopy and quantum chemical calculations to study the interaction between nucleobase uracil and coronene which models the graphene surface. To observe the dimer FTIR spectrum, we use a quartz microbalance that allows us to produce matrix samples with precisely determined concentrations of coronene and uracil (with the concentration ratio of 2.5:1:1000

The main features of the secondary emission mass spectrometry probing of condensed systems containing compounds of biological significance at low temperatures are summarized. The possibilities of distinguishing mass spectra of the solid and liquid phases of simple organic compounds and water as the medium for bio-molecules, monitoring of phase transitions and nonequilibrium processes are illustrated

Based on the self-consistent Hartree–Fock approximation, the nonstationary equation is obtained for the one-particle wave function describing the Bose–Einstein condensate in a rarefied gas of spin-zero bosons. A rarefied gas of bosons is exposed to the static external field, which ensures its finite ground state. The derived equation allows one to correctly determine the ground state energy in the

The application of various action spectroscopy and absorption spectroscopy methods for studying the structure of biological molecules and their constituent fragments in an isolated state is considered. The main attention is paid to the results achieved in the study of the nucleosides which are the structural units of DNA and RNA. It has been demonstrated that modern low-temperature spectroscopy methods

The biological molecules delivered to Earth on the board of meteorites and comets were called one of the possible causes of the origin of life. Therefore, our understanding of the routes of formation of biomolecules in space should shed a light on the possibility of the existence of habitable extrasolar planets. The large abundance of organic molecules is found in the space regions with the lowest

Noncovalent interaction between semiconducting single-walled carbon nanotubes (SWNTs) and graphene oxide (GO) in composite films (GO-SWNTs) was analyzed by Raman spectroscopy in the range of D and G modes (1170–1780 cm−1). Comparison between Raman spectra of composite film and single-component GO and SWNTs films showed that the interaction between GO and SWNTs is accompanied by a band broadening and

The possible role of molecular products of cell radiolysis, in particular, hydrogen peroxide molecules, in blocking DNA activity in cancer cells during irradiation with heavy ions is investigated. It is supposed that hydrogen peroxide molecules can form long-lived molecular complexes with DNA atomic groups and, thus, prevent the realization of genetic information in the biological cells. Using the

The ferromagnetic resonance (FMR) spectra of Fe3O4 and ZnFe2O4 nanoparticles with organic synthesis products were studied at T = 4.2 K. It was determined that the sintering of nanoparticles induced by postsynthesis heat treatment forms a mechanically unstable transition layer between them. Changes in the FMR spectra of Fe3O4 nanoparticles synthesized by precipitation in microemulsions using octylphenol

The optical absorption, fluorescence, phosphorescence in UV and visible spectral range, and effect of light irradiation on spectral properties of DNA with the presence of nickel ions are studied. The quantity of nickel ions varies from 1 ion per 500 base pairs of DNA to 2 ions per base pair. Three important features fixed: the shape of fluorescence and phosphorescence spectra of the DNA do not change

Original fundamental properties of Yanson point contacts allow their application to research and technology development at a wide range of surrounding conditions. At low temperature these nanoobjects can be used as a main instrument of Yanson point-contact spectroscopy. At room temperature they can serve as a sensitive element of advanced nanosensors with excellent performance. The most important advantage

Computer simulations of an argon fcc crystal fragment with embedded water clusters of different sizes are performed using the quantum mechanical DFT/M06-2X method. The effect of the argon matrix on the structural, energy, and spectral parameters of individual water clusters are investigated. The formation energies of (H2O)n@Arm complexes, as well as deformation energies of water clusters and of the

A feature of biological systems is their high structural heterogeneity. This is manifested in the fact that the processes observed at the nanoscopic level are noticeably multistage in time. The paper expounds an approach that allows, basing on the methods of nonequilibrium statistical mechanics, to obtain kinetic equations that enable describing the evolution of slow processes occurring against the

Within the framework of the theory of strongly-interacting quantum Bose liquids, we consider a general relativistic model of self-interacting complex scalar fields with logarithmic nonlinearity taken from dense superfluid models. We demonstrate the existence of gravitational equilibria in this model, described by spherically symmeric nonsingular finite-mass asymptotically-flat solutions. These equilibrium

The temperature dependences of resistance of n-type conductivity Bi2Se3 whiskers with doping concentration (1–2)⋅1019 cm−3 were studied in the temperature range 1.6–300 K. The sharp drop of the resistance was detected that is a result of a partial transition to the superconductive state at the critical temperature Tc = 5.3 K and probably due to the inclusion of β-PdBi2 phase in the studied samples

An observed correlation between the critical temperature of a superconducting transition in high-temperature superconductors and a proximity of their electronic structure to the topological Lifshitz transition needs to be verified on simple model materials. Here we show that such an object could be a Mo–Re alloy with an equal concentration of constituent elements. We present new evidence of the presence

For the first time, studies of the temperature dependences of the thermoelectric power for various compositions of Bi2Sr2CaxZn1−xCu2O8+y (x = 1; 0.8; 0.4) in the range 77–320 K have been carried out. The obtained experimental results are analyzed within the framework of the Xin’s two-band model. The concentration of holes per copper atom and the band gap of the semiconductor type Bi–O layers are determined

For the first time, the temperature dependences of the electrical resistivity ρ(T) were studied in GdxPb1−xMo6S8 (x = 0.5, 0.7, 0.9) compounds in the temperature range 4–18 K and magnetic fields up to 14 T. It is shown that the superconducting transition temperature values Tc decrease from 14.6 K for a compound with x = 0.5 to 11.8 K for x = 0.9. Experimental dependences Hc2(T) were plotted and it

Ideal Bose-gas with finite particle number N is investigated. It is shown that the well-known Bose–Einstein distribution of particles over their quantum states consists of two terms — Bose–Einstein term and an additional N-dependent one. The statement that the chemical potential of the ideal Bose-gas should be negative requires to be also corrected. It is obtained that the analytically calculated observables

The Monte Carlo method was used to calculate the relative dispersions of the magnetization Rm, susceptibility Rχ, and heat capacity RC for a weakly diluted impurity Potts model with the number of spin states q = 4. It is shown that the introduction of disorder in the form of nonmagnetic impurities into the two-dimensional Potts model with q = 4 on square lattice leads to nonzero values for Rm, Rχ,

Electric, piezoelectric, and elastic characteristics of the orthorhombic quantum paramagnet are calculated. Using the exact analytical solution it was shown that the electric permittivity, piezoelectric, and elastic modules can manifest strong dependences on the values of the external magnetic, electric field, external strain, and temperature.

The ballistic transmission of the Dirac ultrarelativistic quasielectrons in graphene structures with the rectangular potential barrier is considered, and both the single and the double-barrier structures are analyzed. Within the framework of the continuum model, the transmission coefficient of quasielectrons T is calculated depending on the parameters of the problem. It is believed that there is an

The dependences of electrical conductivity, the Hall coefficient, the Seebeck coefficient, thermoelectric power factor and microhardness of Bi2Se3 polycrystals on the degree of deviation from stoichiometry 59.9–60.0 at. % Se and temperature (77–300 K) were obtained. The samples exhibited n-type conductivity in the studied ranges of compositions and temperatures. The boundaries of the Bi2Se3 homogeneity

Using the models of elastic and dielectric continuum, the system of differential equations is obtained, the exact analytical solutions of which describe the elastic displacement of the medium for nitride-based semiconductor nanostructure and the piezoelectric effect, which is caused by shear acoustic phonons. The theory of the shear acoustic phonons spectrum caused by the piezoelectric potential was

Evolution of the nonequilibrium inhomogeneities and topological defects is studied in terms of complex kink solutions of the sine–Gordon equation. The weakly damped oscillation of the sine–Gordon kink, named as the kink quasimode, is described explicitly. It is shown that the oscillatory kink behavior and the wave packet generation depend significantly on the initial nonequilibrium kink profile. In

The effect of high hydrostatic pressure up to 12 kbar on the electrical resistivity in the basal ab plane of an optimally doped Y0.77Pr0.23Ba2Cu3O7−δ single crystal was studied. An inhomogeneity of the sample is found that does not depend on the applied pressure, P. The Tc(P) dependence increases nonlinearly with increasing P, and the value of the baric derivative, dTc/dP, decreases. Possible mechanisms

It is shown that the experimental data on the temperature dependences of the effective electrical resistance and thermal conductivity in the range of 4.2–300 K of the electroconsolidated Fe0.5Ni0.5 composite are within the Hashin–Shtrikman boundaries for the conductivities of a three-phase system. The components of the system are pure Fe and Ni, and the intergranular medium in the form of an alloy

The optical properties of C60 single crystals, intercalated with nitrogen molecules, were studied by the spectral-luminescence method at a temperature T = 30 K and excitation by the He–Ne laser (Eexc = 1.96 eV). Intercalation was carried out at a pressure of 30 atm in a temperature range of 200–550 °C. It was found that at sorption temperatures up to 400 °C, the bands of the low-temperature luminescence

We present an experimental study of the thermo emf of a two-dimensional electron-hole system in a 21 nm HgTe quantum well in the presence of magnetic field. The first experimental observation of Nernst-Ettingshausen effect in a 2D semimetal is reported. The comparison between theory and experiment shows that the thermo emf is determined by two contributions: the diffusion and the phonon drag, with

Quasiclassical calculations of the effective cyclotron mass and the spectrum of Landau levels have been carried out for carriers of the size-quantized H2 subband with a nonmonotonic dispersion law, which forms a valence band of 20.5-nm-wide HgTe quantum well with an inverted band structure. The model of the so-called “extremum loop”, previously developed by Rashba and Sheka for semiconductors with

The longitudinal ρxx(B, T) and Hall ρxy(B, T) resistances are experimentally investigated in n-InGaAs/GaAs nanostructures with a single and double quantum wells in the magnetic field range B = 0–2.5 T and temperatures T = 1.8–20 K. It is shown that the origin of the temperature-independent point located at ω c τ ≅ 1 on the ρxx(B, T) curves is due to the combined action of the classical cyclotron motion