The relative stability of diamond and graphite is readdressed from the new perspective of deductive molecular mechanics. Unlike most theoretical studies that are conducted numerically, this article uses an analytical model to gain insight into the fundamental reasons behind the quasi-degeneracy of these allotropes with very different bonding patterns. The relative energies of the allotropes are derived

Current-voltage characteristics of a single-electron transistor with a vibrating quantum dot were calculated assuming vibrons to be in a coherent (non-equilibrium) state. For a large amplitude of quantum dot oscillations we predict strong suppression of conductance and the lifting of polaronic blockade by bias voltage in the form of steps in I-V curves. The height of the steps differs from the prediction

The linear response of the molecular aggregate chain with the random distribution of the strength of the neighboring intermolecular interactions to the bichromatic electromagnetic field has been calculated. The presence of the linearly polarized field produces additional resonance absorption at the combined frequencies of the circularly polarized and linear polarized field. The strength of the absorption

The magnetic properties of narrow zigzag graphene nanoribbons with periodically embedded atoms of transition metals have been studied in the framework of Heisenberg spin Hamiltonian. We have proposed the simple effective model to give a semi-qualitative description of the peculiarities of magnetization profiles of the systems under consideration. This model can be used for an arbitrary value of spin

The Wolff cluster Monte Carlo algorithm is used to investigate the effect of frozen nonmagnetic canonically distributed impurities on the phase transitions in a two-dimensional Potts model with the spin state q = 5. Systems with linear dimensions L = 20–160 at spin concentrations p = 1.0 and 0.9 are considered. Using the fourth-order Binder cumulant method and the histogram analysis method it is shown

The phase transitions and critical properties of the three-dimensional stacked triangular-lattice Ising antiferromagnet in a magnetic field are studied using the replica Monte Carlo method. The nature of the phase transitions is analyzed on the basis of the histogram method. It is established that a second-order transition occurs in the field range of 0 ≤ h ≤ 6. At a high field, the degeneracy of the

Structural, magnetic, and thermal studies of DyCr3(BO3)4 have been carried out. Structural studies showed that the sample contains two phases, with the contents of the rhombohedral (R32) and monoclinic (C2/c) phases being the same, within the accuracy of the method. The lattice parameters for each phase were determined (the rhombohedral: a = 9.461 Å, c = 7.488 Å; the monoclinic: a = 7.394 Å, b = 9

The dependence for the frequencies of the internal modes on the external field in spiral structures in easy-plane antiferromagnets with a small in-plane anisotropy are studied theoretically in a wide region of the fields including the spin-flop transition field. The theoretical results are compared with the known experimental data for the antiferromagnetic resonance in NdFe3(BO3)4. This comparison

This article investigates the dynamic properties of two-dimensional nonlinear magnetic metamaterials consisting of nanoscale elements. The authors propose a model for a two-dimensional lattice of capacitively and inductively coupled split rectangular nanoresonators. It has been shown that the long-wave dynamics of this two-dimensional lattice are described by a regularized two-dimensional nonlinear

Spin valves based on materials in which the spin-flip is suppressed by the spatial separation of charge carriers, while maintaining electric neutrality in the valve volume, are considered. The possibility of using these valves as electric batteries is discussed. Regulating the potential difference on the valve, one can expect the effects of incommensurability of the type of “devil's staircase” associated

Magnetic circular dichroism (MCD) and absorption spectra of multiferroic HoFe3(BO3)4 of 5I8 → 5F2 and 5F3 f–f transitions are measured at T = 90 K. The absorption spectra are expanded into Lorentzian components, and the transition intensities are obtained. The Zeeman splitting of some transitions is determined using the MCD and absorption spectra. The MCD spectra and Zeeman splitting are theoretically

The smooth (001) surfaces of SrTiO3 (STO) single crystals were investigated by the reflection high-energy electron diffraction method in the temperature range from 5.5 to 300 K. The Raman scattering confirmed the high quality of STO samples. Five structural anomalies were found depending on temperature. The antiferrodistortive phase transition from the cubic structure to tetragonal, observed in the

The review is devoted to the conductive properties of the multielement compounds such as lanthanum and erbium cobaltites. These properties are associated with a dopant-controlled interaction of the delocalized electrons with the local magnetic moments. It is considered the basic physical mechanisms that determine the transport properties of perovskitelike materials. It is given main experimental results

Magnetoconductivity oscillations and absolute negative conductivity induced by nonequilibrium populations of excited subbands in a degenerate multisubband two-dimensional electron system are studied theoretically. The displacement from equilibrium, which can be caused by resonant microwave excitation or by any other reason, is assumed to be such that electron distributions can no longer be described

The propagation of intense rectangular thermal pulses in superfluid helium is studied numerically using superfluid turbulence hydrodynamics with various equations for vortex line density dynamics. It is shown that the experimental data are most adequately described by the Vinen equation. The impact of the background vortex line density on the dynamics of the pulses at different temperatures of the

In this work, we analyze the temperature dependencies of resistance and magnetoresistance for two RuSr2(Eu1.5Ce0.5)Cu2O10−δ ceramic samples, one of which was left in the as-prepared state while another one was oxygen saturated. The measurements on these samples were made soon after preparation and repeated after their long storage (10 years) in an ambient atmosphere when they lost most of their over-stoichiometric

The authors have detected an anomalous X-ray optical effect in the Ni(1−x)Wx/TiN system, which consists of a rise in the intensity of certain diffraction lines of the substrate with increasing coating thickness. Based on the observed effect, this article has conceptualized the optimization of the architecture of two-layer systems with a substrate of TiN-coated NiW paramagnetic alloys, which provides

This study analyzes a non-threshold electromagnetic radiation detector, which is a current-carrying superconducting film with a normal domain. The normal domain is formed as a result of heating a portion of the film by an external heat source, and Joule heat in the domain. The detection mechanism consists in the fact that the heating of the film by electromagnetic radiation leads to an increase in

The Ginzburg–Landau method is used to conduct a phenomenological analysis of how the sample thickness impacts the incommensurate spin states in the TbMnO3 centrosymmetric ferroelectromagnet. The analysis is performed using the first-harmonic approximation, and provides a qualitative confirmation of the experimentally observed decrease in the film modulation vector at a decreasing temperature, as well

The crystal structure, magnetic susceptibility as a function of temperature χ(T) in the range 5–400 K, and the hydrostatic pressure effect on χ at fixed temperatures T = 78, 150, and 300 K, were studied in perovskite-like compounds La1−xPrxCoO3 (x = 0, 0.1, 0.2, and 0.3). The obtained experimental data were analyzed using a two-level model with an energy gap Δ between the ground and excited states

The ferromagnetic resonance (FMR) in the shape memory alloys (SMAs) exhibiting structural cubic-tetragonal phase transition has been studied. The influence of instability and spatial inhomogeneity of crystal lattice on the FMR spectra of twinned ferromagnetic SMAs films has been analyzed using statistical model of ferromagnetic martensite. It has been shown that the abnormally strong temperature dependence

The temperature evolution of the LiNiPO4 single crystal Raman spectra in a region of 2–25 K, which includes a phase transition to a magnetically ordered state, is studied. For the first time, magnetic contribution in the Raman spectra was divided into single-magnon and two-magnon excitations at 2 K. The energies of the detected single-magnon excitations are in good agreement with the data obtained

A combined superconducting magnetic system with a uniform field of up to 20 T has been developed. The system contains several solenoidal sections and a magnetic flux concentrator consisting of hydroextruded dysprosium. The sections are wound from NbTi, Nb3Sn wires and Nb3Sn ribbon. A magnetic shield made out of Nb3Sn ribbon is applied in order to increase the uniformity of the magnetic field. The magnetic

The dependences of the current and integral intraband terahertz electroluminescence intensity on the electric field in the n-InGaAs/GaAs heterostructures with asymmetric double tunnel-coupled quantum wells under the conditions of bipolar lateral transport are established to differ qualitatively for different interwell barrier widths. In the case of the thick (∼50 Å) barriers at electric fields less

The temperature dependences of the longitudinal and transverse conductivity of YВа2Сu3О7−δ single crystals irradiated with high-energy electrons were measured. It was found that, in contrast to unexposed YВа2Сu3О7−δ single crystals, the absolute value of the electrical resistivity anisotropy ρc/ρab significantly decreases with an increase in the number of structural defects in the experimental sample

This article investigates the magnetic susceptibility, χ(T), of the two-phase (R32 + C2/c) crystal LaCr3(BO3)4 in the temperature range 2–300 K for two orientations of an external magnetic field. It has been established that both structural modifications of lanthanum chromium borate are ordered antiferromagnetically, with each of them having its own Néel temperature (6.5 and 8.5 K). It has been shown

The temperature dependences of the offset yield strength, strain-rate sensitivity of deformation stress, and the activation volume of plastic deformation in VT1-0 nanocrystalline titanium, have been determined under quasistatic tension in the temperature range 4.2–395 K. Thermal activation analysis of experimental data has been performed. The low-temperature plasticity of nanocrystalline titanium is

The paper reviews the theory of the long-distance spin superfluid transport in solid ferro- and antiferromagnets based on the analysis of the topology, the Landau criterion, and phase slips. Experiments reporting evidence of the existence of spin superfluidity are also overviewed.

A phase-coherent state of electron–hole pairs may emerge in two-layer n–p systems, which is generated by the Coulomb attraction of electrons of the n-layer to holes of the p-layer. Unlike a Josephson junctions, the order parameter phase in n–p bilayers is locked by interlayer tunneling matrix elements T12. The phase locking determines the response of the electron–hole condensate to the electric voltage

We briefly discuss theoretical and experimental discoveries in the field of supertransport and plasticity in imperfect solid 4He and argue that these promise new exciting developments. Several experiments aimed at clarifying the origin of the supertransport and its relation to plasticity are proposed. In particular, we argue that “cold-working” protocols of sample preparation should be crucial in this

Using coherent-state formalism (the Keldysh formalism), the article describes a transition from a homogeneous superfluid state to a supersolid state in a two-dimensional dilute gas of electron-hole pairs with spatially separated components. Such a transition is heralded by the appearance of a roton-type minimum in the collective excitation spectrum, which touches the abscissa axis as the distance between

The thermodynamic equilibrium in a system of randomly quantized vortices in superfluid helium with counterflow between the normal and superfluid components is considered. Both continuum and discrete approaches are studied. Even when using the continuum approach for the system as a whole, the partition function for the various vortex loop configurations can only be calculated by involving the discrete

We investigate the collective density oscillations and dissipationless drag effect in bilayer structures of ultra-cold bosons in the presence of counterflow. We consider different types of inter-particle interactions and obtain the drag coefficient and effect of counterflow on the sound velocity. We observe that counterflow enhances (suppresses) the energy of symmetric (asymmetric) density mode and

The theory of L. D. Landau is used to conduct a hydrodynamic and thermodynamic examination of a number of issues related to the phase transition of He II to He I in the presence of macroscopic motion. In particular, it is shown that the transition in rotating helium is a first-order transition.

The vibrational modes in isotropic nonpolar dielectrics He I and He II are studied in the presence of an alternating electric field E = E0izsin(k0z–ω0t), by solving the equations of ordinary and two-fluid hydrodynamics. There is a “coupling” between the electric field and the density fluctuations, since the density gradient leads to the spontaneous polarization Ps, and the electric force contains the

The nonlinear stage in the evolution of anisotropic beams of high-energy and low-energy phonons is considered. The beams are interacting systems that are virtually one-dimensional in phase space. The observations and theoretical approaches to the space and time evolution of these systems are analyzed in the general case, when they are bounded in both the longitudinal and transverse directions. As a

For the recently proposed exactly solvable two-chain correlated electron model with the anisotropic spin-spin interaction between electrons and the spin-orbit interaction the ground state persistent currents are calculated. The model describes the quasi-one-dimensional type II superconductor. It is shown, that the spin-orbit coupling determines the initial phase of oscillations of charge and spin persistent

We examine the superfluid states that emerge in the Kane–Mele model as a result of the on-site short-range attractive interaction U. The collective-mode dispersion is defined by the solutions of the Bethe–Salpeter (BS) equation in the generalized random phase approximation. The slope of the low-energy (Goldstone) mode and the corresponding sound velocity at half filling, calculated within the BS formalism

We consider the dynamics of exciton condensed phase pulses in two interacting quantum wells, in which excitons are excited and are acted upon by an external driving force. We use the phenomenological expression of free energy for excitons and take into account the finiteness of the exciton lifetime. It is assumed that the excitonic condensed phase arises due to the interaction between excitons, and

The nonlocal optical response of a layered high-temperature superconductor slab embedded in a dielectric medium is theoretically studied. It is assumed that the layers inside the high-temperature superconductor are parallel to the slab surfaces. We calculate its p-polarization optical spectra by using an average permittivity tensor which depends on both the frequency and the wave vector of the electromagnetic

The temperature dependence of excess conductivity σ′(Т) has been studied in three polycrystalline samples of the FeSe0.94 superconductor, prepared by different technologies. The measured temperature dependences of the Δ*(T) parameter, which is associated with the pseudogap in cuprates, were analyzed using the local pair model. At high temperatures, all three samples exhibit a high narrow maximum along

This study establishes the identity of the topological phases that emerge in the Josephson medium of granular high-temperature superconductors YBa2Cu3O7–δ in the process of the Berezinskii–Kosterlitz–Thouless (BKT) phase transitions, under the influence of an external magnetic field and transport current. The nature of the topological phases arising as a result of the BKT phase transition was found

The theory of collectivization of valence electrons is used to estimate the characteristic values of pressure that may cause the superconductivity of hydrogen compounds (hydrides) at room temperatures. The calculated values are compared with experimental data obtained during the study of LaH10 compounds: Тc ≈ 250 K, Р ≈ 170 GPa.

We numerically examine vortices interacting with pinning arrays where a portion of the pinning sites have been removed in order to create coexisting regions of strong and weak pinning. The region without pinning sites acts as an easy-flow channel. For driving in different directions with respect to the channel, we observe distinct types of vortex flow. When the drive is parallel to the channel, the

Here we describe the development of a computer algorithm to simulate the Time-Dependent Ginzburg-Landau equation (TDGL) and its application to understand superconducting vortex dynamics in confined geometries. Our initial motivation to get involved in this task was trying to understand better our experimental measurements on the dynamics of superconductors with vortices at high frequencies leading

The effect of the magnetic field renormalization in superconducting nanostructured materials is quantitatively evaluated. For demonstration purposes, three superconducting structures with various geometric shapes and dimensions and functioning in different resistive regimes are considered. Simulation is based on a set of equations including the time-dependent Ginzburg-Landau equation coupled with the

The angular dependence of magnetic-field commensurability effects in thin films of the cuprate high-critical-temperature superconductor YBa2Cu3O7−δ (YBCO) with an artificial pinning landscape is investigated. Columns of point defects are fabricated by two different methods of ion irradiation — scanning the focused 30 keV ion beam in a helium ion microscope or employing the wide-field 75 keV He+ beam

Dependence of the critical current on the misorientation angle in high-temperature superconductor (HTS) [001]-tilt bicrystal is theoretically examined. It’s argued that in the case of relatively small values of the bicrystal misorientation angle θ (θ ≤ 10–15°) the critical current as well as the resistive state emergence are determined by depinning of Abrikosov vortices, which are locked by c-oriented

In this paper we present a short overview on the results that can be obtained through the study of vortex motion at high frequencies. The phenomenological force balance for isolated-like vortices shaken by microwave currents and subjected to viscous drag, pinning forces and thermal creep is recalled and physically presented. The derived vortex motion resistivity, together with the main vortex parameters

In this paper we present an overview of the microwave properties of a surface electromagnetic wave resonator (SEWR) made on the basis of a superconducting film, and also consider possible applications of such resonators to create various microwave devices. Features of such a SEWR are the simplicity of its design (such a resonator, in fact, can be just the superconducting film itself on a dielectric

Within the framework of the proposed generalization of the phenomenological model of a microwave nonlinear HTSC transmission line, the effects of direct current on the transmission line are studied. Taking into account the next term in the expansion of the nonlinear dependence of the resistance on current allows us to explain the anomalous dependence of the insertion loss on the input power level observed

Technological applications of NbN thin films may be threatened by the development of magnetic flux avalanches of thermomagnetic origin appearing in a large portion of the superconducting phase. In this work, we describe an approach to substantially suppress the magnetic flux avalanche regime, without compromising the upper critical field. This procedure consists of depositing a thin Nb layer before

We discuss two possible mechanisms of the flux flow instability (FFI) in type II superconducting strips. While the nature of nonequilibrium effects leading to this instability is widely accepted (Joule heating and finite relaxation time of the superconducting order parameter) still there is a question how FFI develops in space. According to one scenario instability occurs simultaneously in the whole

We have studied vortex dynamics in superconducting materials at very high vortex velocities as a function of the applied magnetic field. High velocity vortex dynamics can become critical, so that an instability occurs, leading the system to quench abruptly to the normal state. The presence of pinning mechanisms in all superconductors not only is able to foster high critical currents but it can strongly

Ultrathin microstrips based on polycrystalline NbRe films were investigated in order to preliminarily test the suitability of this material for the realization of superconducting single-photon detectors. The voltage-current characteristics measured on these samples show clear hysteresis. This is a fundamental ingredient for investigating single-photon detection as well as single vortex fluctuation

Nowadays, the interaction between phonon and magnon subsystems of a magnetic medium is a hot topic of research. The complexity of phonon and magnon spectra, the existence of both bulk and surface modes, the quantization effects, and the dependence of magnon properties on applied magnetic field, make this field very complex and intriguing. Moreover, the recent advances in the fields of spin caloritronics

Conductance-voltage characteristics (CVCs) of tunnel break junctions made of Bi2Sr2CaCu2O8+δ crystals were measured. It was demonstrated that the CVCs have a V-shaped inner gap region, similar to those typical of CVCs for tunnel junctions between d-wave superconductors. The CVCs have different forms for different junctions, but all of them reveal weak dip-hump structures outside the inner gap region

A short overview of theoretical models for the description of the relaxation processes in metals excited by a short laser pulse is presented. The main effort is given to description of different processes which are taking place after absorption of the laser pulse. Widely used two-temperature model is discussed and the conditions of applicability of this model are identified. Various approaches for

Crossed electric and magnetic fields influence dipolar neutral particles in the same way as the magnetic field influences charged particles. The effect of crossed fields is proportional to the dipole moment of the particle (inherent or induced). We show that this effect is quite spectacular in a multilayer system of polar molecules. In this system molecules may bind in chains. At low temperature the

The current in a superconducting closed loop containing a thin-film interferometer with two point contacts (two Josephson-type weak links) has been measured as a function of the transport current and external magnetic field applied to interferometer. The differences between the transport and magnetic dependences of the system under study and similar characteristics for a superconducting closed loop