bluuebunny/crossref_metadata_2025 huggingface dataset:
“Orthogonal” holes and hybridized electron spectrum of CuO2 planes
Authors: Loktev V. M.
Published: January 2025

Proceeding from an assumption on the mutual orthogonality of the spin quantization axes of free and localized holes, we have found the hybridized electron spectrum of CuO2 planes in high-temperature superconductors. It is shown that the spin projection conservation law in this case does not hinder the hybridization of oxygen holes with copper ions of both magnetic sublattices.
Transient state and steady-state magnetization in a one-dimensional magnet after the application of a magnetic field
Authors: Zvyagin A. A. , Segal Ya. Yu. , Tsukernik V. M.
Published: January 2025

The response of the uniaxial two-sublattice and the biaxial one-sublattice X–Y models to a steplike variation of the applied magnetic field oriented along the z-axis is considered. It is shown that the variation of the magnetization does not depend on the magnitude of the finite field under certain conditions (the biaxial one-sublattice X–Y model in the ground state, the initial field tends to infinity). Besides, it is shown that in contrast to static susceptibility, the dynamic susceptibility of the biaxial one-sublattice X–Y model has a jump at a certain value of the magnetic field at a nonzero temperature.
Point-contact resistance and phonon spectroscopy in layered metals
Authors: Kolesnichenko Yu. A. , Tuluzov I. G. , Khotkevich A. V.
Published: January 2025

The nonlinear electrical conductivity of point contacts between layered metals is investigated theoretically.The anisotropy of point-contact spectra of the electron – phonon interaction, which is associated with the quasi-two-dimensional nature of the energy – momentum relation, is analyzed.
Magnetoplasma waves in compensated metals with quasilocal electron states
Authors: Ermolaev A. M. , Shurduk A. I.
Published: January 2025

The effect of quasilocal electron states on transverse magnetoplasma waves in compensated metals is considered. It is shown that the coupling of magnetoplasma resonance with the electron resonance at an impurity results in the emergence of two branches in the magnetoplasma wave spectrum, which are separated by a forbidden frequency region (quasigap). The spectrum and damping decrement of the waves are calculated. The effect of the waves on the surface impedance of metals is considered. The resonance of impedance is observed at the upper boundary of the quasigap.
Effect of hydrostatic pressure on the critical temperature of niobium diselenide with tin impurity
Authors: Chashka Kh. B. , Obolenskii M. A. , Balia D. D. , Beletskii V. I. , Vovk R. V.
Published: January 2025

The effect of uniform pressure on the superconducting transition temperature of Nb1–xSnxSe2 has been studied experimentally. It is suggested that the observed increase in the superconducting transition temperature with pressure is not associated with the suppression of transition to the change density wave state.
Angular magnetoacoustic oscillations in layered conductors
Authors: Gokhfel’d V. M. , Kirichenko O. V. , Peschanskii V. G.
Published: January 2025

Absorption of ultrasound in a layered metal with a quasi-two-dimensional spectrum of conduction electrons is studied in an external magnetic field H. It is shown that in the strong-field limit, the absorption coefficient oscillates upon a variation of the angle between H and the normal to the layers.
Infrared-active excitations in XY4 molecular crystals (a review)
Authors: Calvani Paolo , Nucara Alessandro , Lupi Stefano
Published: January 2025

The solid phases formed at low temperatures by tetrahedral XY4 molecules (X = C, Si, Ge, Sn; Y = H, D) provide the spectroscopist with a wide choice of site symmetries, orientational structures and molecular motions. These systems are then particularly suitable for an extensive study of such molecular excitations, like vibrons, rotons, and librons. In this paper we review recent results of infrared spectroscopy on solid CH4, CD4, SiH4, GeH4, and we discuss how they may help to understand the behavior of quasi-particles in these complicated systems.
Thermal conductivity of solid H2 in the orientationally ordered phase
Authors: Clarkson David , Meyer Horst
Published: January 2025

New measurements of the thermal conductivity κ and the thermal relaxation time are described for solid H2 in the orientationally ordered phase, and in the order–disorder transition region. The temperature range is between 0.2 and 1.4 K. We confirm the earlier conductivity data obtained in this laboratory and discuss the results pertaining to the ordered phase. However, certain anomalous observations reported previously are not repeated here, and are attributed to the different cell and growth technique. Extrapolation leads again to the suggestion that κ(o-H2) in the ordered phase is of the same order as κ(p-H2). The measurements of the boundaries and width of the order–disorder transition coexistence region are extended to lower and higher temperatures. The conductivity of p-H2 with low o-H2 fractions is also found consistent with previous results in this laboratory, but it is lower than that of larger crystalline samples, presumably more perfect, investigated by Gorodilov et al., and by Bohn and Mate above 1.3 K.
Calculational methods for predicting phase transitions in simple molecular solids
Authors: Etters R. D. , Kuchta Bogdan
Published: January 2025

Techniques are developed for calculating phase transitions in solids where entropy contributions to the Gibbs free energy may be important and/or where large potential barriers between competing phases exist. These methods are applied to solid N2O, CO2, and N2. Results are described.
IR spectra and the structure of cryocondensates of water vapor
Authors: Drobyshev A. S. , Atapina N. V. , Garipogly D. N. , Maksimov S. L. , Samyshkin E. A.
Published: January 2025

The rate of growth and the refractive indices of cryocondensates of water vapor deposited on mirror metal substrates in vacuum have been measured in the temperature interval 15–180 K. Reflection spectra of 0.25–2.5 μm thick layers deposited on these substrates have been measured in the wavelength region 2–20 μm. It is shown that the peculiarities in the condensation temperature dependences of the growth rate and refractive indices of the water vapor cryocondensates are consistent with the temperature ranges of existence of different solid phase structures obtained from the IR spectroscopy data. The effect of structural transitions in a cryocondensate layer on the shape of absorption bands is studied comprehensively in the region of 3 and 10–17 μm.
Sorption properties of vacuum cryocondensates
Authors: Yuferov V. B.
Published: January 2025

It is shown that vacuum cryocondensates of most gases are effective sorbents for hydrogen and helium with a physical adsorption mechanism. The connection of the adsorption parameters with the structural and thermophysical parameters of cryocondensates is discussed.
Free-exciton luminescence of solid xenon and solid krypton
Authors: Varding D. , Becker J. , Frankenstein L. , Peters B. , Runne M. , Schröder A. , Zimmerer G.
Published: January 2025

With time and spectrally resolved experiments, the luminescence of solid Xe and solid Kr was re-investigated. It is the first time that obtained time and spectrally resolved results are consistent with one another. For solid Xe, the luminescence of free excitons turns out to be extremely strong, exceeding the emission of self-trapped excitons by a factor of 50 (peak-to-peak ratio). For the first time, an experimental determination of self-trapping rates without any assumption concerning radiative lifetimes was possible. The numerical values in the low 108 s−1 range are about 4 orders of magnitude smaller than originally estimated. The present values are in good agreement with theoretical predictions.
Quasiresonance transport of excitation energy from a metastable excited atom to an inert gas cryocrystal
Authors: Zhitnikov R. A. , Dmitriev Yu. A.
Published: January 2025

It is found that atomic (2p53s)3P2 centers are formed as a result of trapping of He gas discharge products in the growing neon cryocrystal. The unstable excited states (2p53s)3P2 in neon cryocrystals were observed by the EPR technique, and the effect was interpreted as a new phenomenon manifested in the form of a quasiresonance transport of excitation energy from a metastable 23S1 atom of He trapped in the growing neon cryocrystal to the exciton band of the neon crystal with a subsequent self-trapping of this exciton in the 2p53p-state. This is followed by a decay to the state (2p53s)3P2 which is actually registered in the experiment by the EPR technique. Temperature investigations show that the rate constant λ in the process of excitation energy transfer from a 23S1 atom of He to the exciton band of a neon cryocrystal quite correctly follows the Arrhenius law λ = λ0exp(–E/kT), while the activation energy E of this process is found to be equal to 0.0010(5) eV.
Structural anomalies in solid deuterohydrogen
Authors: Prokhvatilov A. I. , Strzhemechnyi M. A. , Shcherbakov G. N.
Published: January 2025

X-ray studies of pure deuterohydrogen (containing less than 0.4% isotopic impurities) are carried out in the temperature range 4.5–16.5 K. The obtained low-temperature value of the HD hcp lattice volume is V0 = 21.58 cm3/mole. It is was found for the first time that the ratio c/a of the lattice parameters at low temperatures is 1% lower than the ideal value. Such a comparatively large deviation is unusual for solid hydrogens. The observed effect is explained by the presence of “admixtures” of higher rotational states induced by additional stronger (as compared to those in homonuclear isotopes) anisotropic forces associated with the asymmetry of HD molecule. The sign and order of magnitude of the theoretical estimates for ξ=c/a−8/3 are in accord with the experimental data.
Structures studies of Ne–H2 solid solutions
Authors: Baryl’nik A. S. , Prokhvatilov A. I. , Strzhemechnyi M. A. , Shcherbakov G. N.
Published: January 2025

Solid parahydrogen–neon mixtures are subjected to x-ray structure analysis over the entire range of concentrations at temperatures varying from 5 K to the solidus temperature. The initial samples are obtained by condensation from the gaseous phase on a cold substrate. At low concentrations xNe of neon, a number of anomalous phenomena are observed: (1) excess volume per impurity turns out to be large and positive, which is in contradiction with Vegard’s rule; (2) at low temperatures, two systems of hcp reflexes are observed with lattice parameters close to corresponding values for the pure components, and (3) an increase of temperature to the melting point of the alloy with xNe>0.25% leads to a simultaneous change in the symmetry of both systems of reflexes to that of fcc structure which is preserved upon a further temperature cycling. These anomalies can be explained qualitatively by assuming that a neon atom in the hydrogen lattice forms a single metastable complex with the nearest coordination sphere.
Implications of the high pressure critical point of hydrogen on the structure of the H-A phase
Authors: Silvera Isaac F.
Published: January 2025

It has been speculated that the recently observed H-A phase in hydrogen is the metallic molecular phase, but there is both experimental and theoretical uncertainty. Theoretical results are sensitive to the crystal structure. In this paper, based on a symmetry argument, we show that the structure is probably hcp with the molecular distribution having cylindrical symmetry about the crystal c-axis.
A damping system for a setup producing ultralow temperatures
Authors: Rybalko A. S. , Mikheev V. A. , Kolesnik V. I. , Beloborod’ko B. I.
Published: January 2025

A damping system for protecting a setup for obtaining ultralow temperatures is described and its experimentally measured working characteristics are presented. The use of a platform suspended on ropes results in low resonance frequencies of horizontal and vertical vibrations and reduces the effect of vibrations by a factor of tens.
Influence of inelastic scattering of quasi-particles on the superconducting order parameter and the tunnel Josephson current
Authors: Voitenko A. I. , Gabovich A. M. , Shpigel’ A. S.
Published: January 2025

A model is suggested that describes influence of the inelastic scattering of electrons on the temperature-dependent superconducting order parameter Δ(T). The depairing factor ν(T), associated with the inelastic scattering, and the Δ(T) are found from a self-consistent set of equations. Temperature dependences of the superconducting gap Δg and of the critical tunnel Josephson current Ic are calculated. The curves Δ(T), Δg(T), and Ic(T) differ substantially from the respective dependences in the BCS theory, in particular, by an abrupt decrease near Tc. The second-order phase transition to superconducting state becomes a first-order one; the closer to second order the less is the effect of the factor ν(T). The results are in quantitative agreement with experiment for HTSC oxides.
Cutoff current of phase-slip centers
Authors: Dmitriev V. M. , Zolochevskii I. V. , Khristenko E. V.
Published: January 2025

The time-average superconducting current of phase slip centers (PSC) was studied experimentally as a function of the external microwave field power and the temperature. A correlation has been established between the cutoff current and the supercurrent through PSC as well as its dynamic resistance. We assume that Josephson supercurrent oscillations become harmonic under the action of the microwave field which makes the cutoff current vanish.
Low-temperature magnetoresonance absorption in amorphous iron-based magnetic materials
Authors: Belozorov D. P. , Vertiĭ A. A. , Golik A. V. , Tarapov S. I.
Published: January 2025

Temperature dependence of the ferromagnetic resonance linewidth is studied in amorphous iron-based (FexNi100–x)77B13Si10 alloys (x = 7, 8, 9, and 10 at.%) within the temperature range 0.3 to 150 K at a magnetic resonance frequency of ω/2π = 78 GHz. In the region of higher temperatures, 4 to 30 K, the variation of the linewidth with temperature can be consistently described by a universal exponential law. In the low temperature region, 0.3 to 4 K, the line broadening is a linear function of inverse temperature. The obtained results are discussed with account of two possible mechanisms of interaction between the spin wave and the two-level systems in the amorphous magnetic compound.
Magnetic field-induced spatial spin reorientation in dysprosium orthoferrite
Authors: Gnatchenko S. L. , Piotrowski K. , Szymczak R.
Published: January 2025

It is found that at low temperatures T ⩽ 5.5 K, a magnetic field H‖b induces spatial spin reorientation in dysprosium orthoferrite according to the pattern Г1, ⟶ Г1234 ⟶ Г4. The transition from the antiferromagnetic state Г1 to the state Г1234 with a spatial orientation of the ferro- and antiferromagnetism vectors is a second-order phase transition, while the transition from the state Г1234 to the weakly ferromagnetic state Г4 is a first-order phase transition.
New types of surface and bulk nuclear spin waves induced by magnetoelastic interaction
Authors: Stefanovskii E. P. , Tarasenko S. V.
Published: January 2025

Propagation of new types of surface and bulk nuclear spin waves is discovered in magnetically ordered crystals when the interaction of oscillations of the electron spin, nuclear spin, and elastic subsystems are consistently taken into account.
Transverse galvanomagnetic effect in phonon generation regime in bismuth
Authors: Krasovitskii Vit. B. , Bengus S. V.
Published: January 2025

Transverse galvanomagnetic (Ettingshausen) effect has been measured in monocrystalline samples of bismuth. It is found that a transition to nonlinear conductivity regime is accompanied by an increase in the transverse temperature gradient in the sample. Consequently, it has been possible to observe directly the flow of nonequilibrium phonons generated in the Esaki effect regime. The sound generation coefficient, defining the part of the power liberated from the electron system to the nonequilibrium phonon system, has been obtained experimentally. The temperature dependence of nonlinear current–voltage characteristics has been measured and analyzed.
On the theory of spin waves in nonferromagnetic metals with quasilocal electron states
Authors: Ermolaev A. M. , Ul’yanov N. V.
Published: January 2025

New branches of the spin wave spectrum of nonferromagnetic metals with quasilocal electron states have been discovered in a quantizing magnetic field. The spectrum and decrement of waves propagating in any direction relative to the magnetic field are obtained. The differential cross-section of the magnetic scattering of neutrons by one-particle excitations of electrons localized at impurities and by new spin waves is determined for any scattering angle. The energy spectrum of scattered neutrons contains asymmetric peaks outside Stoner sectors associated with scattering by one-particle excitations. Scattering by spin waves leads to a series of Lorentz satellites arranged symmetrically with respect to the undisplaced line.
Mechanically controlled fractured junctions and their possible applications in point-contact spectroscopy
Authors: van Kempen H. , Shklyarevskii O. I.
Published: January 2025

The possibility of using the high-stability point-contact technique developed in Leyden for electron–phonon interaction (EPI) spectroscopy and for studying various mechanisms of electron scattering is discussed. The modification of the technique proposed in the present work makes it suitable for studying practically all types of conductors. The possibility of obtaining high-quality EPI spectra for noble metals is demonstrated. Contacts of small diameter (< 30 Å) reveal a number of anomalies associated with the presence of crystal lattice defects in the vicinity of the microconstriction and with the mesoscopic nature of the investigated objects. The drawbacks of the technique and possible ways of improvement are analyzed.
On a certain possibility of changing the dimensions of an electron system in a three-dimensional crystal
Authors: Lutskii V. N.
Published: January 2025

The possibility of changing the dimensions of the electron system in a three-dimensional crystal under the action of a nonuniform magnetic field is considered.
Magnetic structure, phase transitions, and propagation of electromagnetic waves in La2CuO4
Authors: Krivoruchko V. N. , Primak T. E.
Published: January 2025

The frequency-field diagram and the components of the high-frequency magnetic susceptibility tensor have been obtained for the antiferromagnetic structures that occur in La2CuO4 in a longitudinal magnetic field. The transmissivity of electromagnetic waves through the sample is calculated and detailed analysis is performed for the changes in the transmission spectrum, caused by the changeover of magnetic phases. Polariton effects are shown to be different for different magnetic structures so that changes in the transmission spectrum are characteristic of any of the permissible phase sequence scenarios. The character of the changes can be used to judge the approach to the phase transition points. Thus, the electromagnetic wave transmission spectrum makes it possible to reconstruct the phase diagram, to determine the AFMR frequencies in various phases and, using these, to reconstruct the constants in the spin Hamiltonian of La2CuO4.
Metamagnetic transition in GdCu2 in an external magnetic field
Authors: Podgornykh S. M. , Kourov N. I. , Tsiovkin Yu. N.
Published: January 2025

Magnetization, magnetostriction, and magnetoresistance of a GdCu2 polycrystal have been studied in static magnetic fields up to 12 MA/m at temperatures between 4.2 and 300 K. It is shown that the metamagnetic transition in an external magnetic field occurs as two spin-flip transitions with the initiating participation of the hybridized 3d–5d electron band.
Energy gaps in the spin-wave spectrum of rare-earth orthoferrites in a magnetic field
Authors: Dan’shin N. K. , Kramarchuk G. G.
Published: January 2025

Temperature and field dependences of energy gaps in the spin-wave spectra at the boundaries of the orientational translation have been studied for thulium and ytterbium orthoferrites. It is shown that in transitions induced by a magnetic field, the gaps in the soft-mode spectra of iron as well as the rare earth are independent of temperature (field). A comparison of the results of high-frequency experiments on various ferrites leads to the conclusion that the contribution of longitudinal oscillations of magnetization at temperatures T < 100 K to the energy gaps in TmFeO3 and YbFeO3 is small and depends mainly on the magnetoelastic and dipole interactions, as well as on the dynamic coupling between iron and rare-earth subsystems.
Kinetics and nonequilibrium quasiparticle distributions in superconductors with strong magnetic correlations
Authors: Nersesyan O. N. , Paturyan S. V.
Published: January 2025

The kinetic model of a superconductor with strong magnetic correlations, taking into account the scattering of quasiparticles by antiferromagnetic spin fluctuations, is considered and used to analyze nonequilibrium distributions of quasiparticles arising due to electromagnetic pumping. The possibility of population inversion is demonstrated.
On the effect of dislocations on the chemical potential of conduction electrons in metals
Authors: Natsik V. D. , Smirnov S. N. , Tikhonenkov N. É.
Published: January 2025

The shift of the electron chemical potential level in a metal caused by linear edge dislocations is computed. It is shown that the main effect is due to the departure of a fraction of the electrons from the conduction band to states localized at dislocation lines (dislocation bands).
Intervalley scattering and combination frequencies of Shubnikov oscillations
Authors: Kozlov V. A. , Narimanov E. E. , Sakharov K. A.
Published: January 2025

It is found that intervalley scattering leads to the emergence of combination frequencies in the spectrum of Shubnikov oscillations. An experiment is proposed for determining the rate of intervalley and interband transitions.
Resonant conductance-oscillations of a mesoscopic ring in a high-frequency electromagnetic field
Authors: Aronov I. E. , Krive I. V. , Shekhter R. I. , Jonson M.
Published: January 2025

We study the influence of an ac electric field on the Aharonov–Bohm oscillations of the conductance of an ultrasmall metallic ring. The electric field is produced by a time-dependent component of the magnetic flux, Φ=Φ¯+Φacos(ωt), that threads the mesoscopic ring. We found that resonant tunneling through the energy levels of the ring and through their satellite levels corresponding to absorption or emission of field quanta gave rise to conductance peaks. These are periodic in Φ¯ with period Φ0 = hc/e. For frequencies ω large compared to the energy level spacing in the ring, the main effect is a shift of the levels ∝Φa2. The conductance acquires a quasiperiodic resonance character.
Multiple electron scattering by an impurity and at the N–S boundary. Negative differential conductivity of the N–S–N system
Authors: Kadigrobov A. M.
Published: January 2025

It is shown that on account of the specific nature of the Andreev reflection, the scattering of conduction electrons in a normal metal by an impurity and at the N–S boundary has a complex quantum-interference nature due to multiple (and coherent) scattering of electron and hole waves by the impurity and at the N–S boundary. Conditions are indicated under which the transition of a superconductor to the normal state in a N–S–N system is accompanied by a decrease in the total resistance of the sample and the current–voltage characteristic is S-shaped.
Response of high-temperature superconductors to electromagnetic signals in the presence of dc magnetic field
Authors: Baltaga I. V. , Il’enko K. V. , Golubnichaya G. V. , Kirichenko A. Ya. , Maksimchuk I. G.
Published: January 2025

Time dependence of the electric field E at the surface of HTSC samples in the critical state is studied theoretically and experimentally. The superconductor is placed in an external longitudinal magnetic field and irradiated by a radio wave of finite amplitude. An expression for the field E(t) is obtained for an arbitrary form of the critical current density vs. magnetic field relationship. The function E(t) contains complete information about the superconductor critical state and about anomalies of magnetic flux penetration into the bulk of the sample. A simple contactless method, based on measurements of the field E(t), is suggested for the determination of the parameters of the critical state in HTSC samples.
A contribution to the theory of an antiferromagnetic chain with site spin S = 1
Authors: Zvyagin A. A. , Segal Ya. Yu. , Tsukernik V. M.
Published: January 2025

The behavior of an easy-plane antiferromagnetic spin chain with site spin 1 in an external field is studied theoretically. It is shown that, in the absence of a single-ion magnetic anisotropy in the ground state, the system does not support a phase with zero magnetization in nonzero magnetic field, in contrast to the two-sublattice chain of spins 1/2. A strong single-ion easy-plane anisotropy brings about such a phase.
Structure of condensed n-H2–Ne films
Authors: Kovalenko S. I. , Solodovnik A. A.
Published: January 2025

Electron diffraction studies have been carried out for condensed n-H2–Ne films. In order to extend the range of existence of solid solutions, the mixtures being deposited were preliminarily cooled and then condensed on a substrate whose temperature did not exceed 2.3 K. An analysis of the observed diffraction patterns and concentration dependence of lattice parameters made it possible to determine the range of existence of solid solutions in samples formed under certain conditions. It is found that the limiting solubility of neon in the fee matrix of hydrogen approaches 3 mol.%, while the solubility of hydrogen in neon lies beyond the sensitivity of the electron diffraction technique and hence does not exceed 0.6 mol.%.
Low-temperature broadening of magnetic resonance line in polarized nuclear target materials
Authors: Tarapov S. I.
Published: January 2025

Temperature dependence of the electron paramagnetic resonance linewidth is studied in the material of the polarized nuclear target based on a stable chromium complex dissolved in propylene glycol (HMBA(Crv)Na). Experiments were carried out at a frequency of 75 GHz in the temperature range 0.3–4.2 K. It is shown that the temperature broadening of the line in such a structurally disordered magnet is described quite well by the model of magnetic two-level systems. This leads to the assumption that a frozen disordered spin system is formed in such polarized nuclear target materials, just like the spin-glass state in magnets with a strong exchange interaction.
Superconducting transition in crystals without inversion center
Authors: Poluéktov Yu. M.
Published: January 2025

The thermodynamics of the superconducting transition is considered for crystals whose point group does not include inversion. It is shown that in connection with the singlet and triplet Cooper pairs present in the condensed state of such superconductors, the number of complex-valued order parameter components is twice the dimensionality of the irreducible representation that corresponds to this superconducting transition. The thermodynamic properties and stability of the superconducting state in crystals without inversion center are discussed on the basis of a generalized Ginzburg–Landau approach.
Effect of external magnetic field on the spectrum and damping of carriers in Hubbard’s one-band model
Authors: Zerov Yu. É. , Loktev V. M.
Published: January 2025

The influence of an external magnetic field on the energy of electron (hole) bands and the damping of carriers is considered in Hubbard’s one-ion model near half-filling level. It is shown that the required spectral characteristics change linearly with the external magnetic field applied at right angles to the antiferromagnetism vector, and that the damping of carriers decreases. This makes it possible to provide at least a qualitative explanation for the isotropic negative magnetoresistance observed in La2–xSrxCuO4 for low values of x.
Optical properties of bismuth films
Authors: Abbosov B. , Akhmedov S. Sh. , Murtazaev A. P.
Published: January 2025

Optical absorption spectra of Bi films are studied in the visible, infrared and ultraviolet spectral regions in the temperature range 4.2–300 K. The spectra of absorption and interband transition energy are compared with Fal’kovskii’s theoretical analysis for bismuth.
Low-temperature quenching of YBa2Cu3O7–δ single crystals
Authors: Mamalui A. A. , Palatnik L. S. , Bednov K. V. , Obolenskii M. A. , Bondarenko A. V.
Published: January 2025

We studied the effect of low-temperature quenching at Ta= 100–300 K on the superconducting transition temperature Tc of YBa2Cu3O7–δ single crystals and their electrical resistance (in the plane ab) in the normal state. Just as in the case of ceramics, the single-crystal samples exhibit Tc increases. The increase of Tc depends on the quenching temperature Ta and the waiting time at Ta before quenching. The experimental results give evidence of a microdiffusion mechanism of formation of the state of the YBa2Cu3O7–δ lattice with elevated Tc values. The non-equilibrium state after quenching is unstable even at T ≳100 K. Isochronous annealing curves were examined. For single crystals, the increase of Tc upon quenching correlates with the decrease of the electrical resistance at a fixed temperature. The character of the variation of the electrical resistance with quenching temperature suggests a disordering of the initial state of oxygen vacancies and their subsequent ordering, i.e., a transition from one type of vacancy superstructure (VSS) to another (VSS’) occurs by way of a thermal activation via an intermediate disordered state.
Effect of plastic deformation at 4.2 K on the structure and the superconducting transition temperature of zirconium
Authors: Aksenov V. K. , Lazarev B. G. , Ledenev O. P. , Sokolenko V. I. , Starodubov Ya. D. , Fursa V. P.
Published: January 2025

We have studied the effect of deformation by extension at 4.2 K, with subsequent warmup to room temperature, on the defect structure and the superconducting transition temperature Tc of zirconium samples prepared by electron beam melting. The substantial increase of Tc (by 20%) is caused by superconductivity enhancement in plastic deformation localization areas at twin boundaries and is due to an effective change of the inter-electron attraction constant.
Frozen electron phase in layered conductors and HTS
Authors: Slutskin A. A. , Gorelik L. Yu.
Published: January 2025

The ground state and superconducting properties of a layered sd-electron system formed by “s-layers” of wide-band s-electrons and “d-layers” of narrow-band d-electrons are investigated. It is shown that over a wide range of electron densities of state (including “metallic” values), the long-range (weak screening) character of Coulomb forces between electrons associated with the layered nature of the system leads to the formation of a new state in d-layers, viz., the “frozen” electron phase having an incommensurate structure in general and differing qualitatively from a Wigner crystal. The spectrum of elementary excitations of such an “electron glass” (“EG-excitations”), which were found to be electron transitions in spatially localized two-level system, is studied. It is shown that the Coulomb sd-interaction, which causes a virtual exchange by EG-excitations between s-electrons, leads to effective ss-attraction and to superconductivity of purely “Coulomb” origin. Expressions are obtained for the gap and superconducting transition temperature Tc. It is shown that Tc can attain values of the order of the d-band width. Peculiarities of the gap structure associated with the layered nature of the sd-system and the specific features of the EG-excitation spectrum are studied.
Impurity states of a quasi-two-dimensional ferromagnet
Authors: Krivoruchko V. N. , Shestakov A. A.
Published: January 2025

The spectrum of impurity states of a quasi-two-dimensional ferromagnet is studied. The energies of s-, p-, d-, and f- states are determined as functions of the exchange interaction of an impurity atom with matrix atoms for various ratios of inter- and intralayer exchange interactions between matrix atoms. It is shown that, unlike in the three-dimensional case, local s1 and d-states can exist for a weakly coupled impurity.
Hydrodynamic approach for describing magnetic properties of β- phase of solid oxygen
Authors: Lavrinenko N. M.
Published: January 2025

The symmetry analysis developed by I. M. Vitebskii and N. M. Lavrinenko {Fiz. Nizk. Temp. 19, 535 (1993) [Low Temp. Phys. 19, 380 (1993)]} and the method of quasi-averages are used to describe the statistical equilibrium state of β-oxygen. The consistent microscopic derivation of the equations of motion is based on a brief description technique (functional hypothesis).
The Fermi surface of Pd2Si
Authors: Antonov V. N. , Yavorsky B. Yu. , Nemoshkalenko V. V. , Antonov VI. N. , Jepsen O. , Andersen O. K.
Published: January 2025

The Fermi surface of palladium disilicide has been calculated using the Linear Muffin-Tin Orbital (LMTO) method. The Fermi surface consists of three small hole pockets, an open hole surface, and two large electron sheets. The calculated angular dependence of the extremal Fermi surface cross-section areas are in reasonable agreement with recent de Haas–van Alphen (dHvA) experiments. Some additional dHvA oscillations are predicted.
Quasioptical method of measuring extremely low dielectric losses in condensed media
Authors: Ganapol’skii E. M. , Golik A. V. , Korolyuk A. P.
Published: January 2025

A quasioptical method for measuring extremely low dielectric losses in crystals and liquids at low temperatures in the millimeter and submillimeter radiofrequency ranges is described. The method is based on the use of an insulating sphere made of the material under investigation as the measuring cavity in which a short electromagnetic field pulse excites a set of “whispering gallery”-type natural oscillations with extremely low radiation losses. Measurements are made by using the oscillation with the longest lifetime, for which the radiation losses caused by inhomogeneities of the material of the sphere are minimum. The method was used for measuring tan δ at a frequency of 36.7 GHz in a ruby crystal for which tan δ is found to be equal to 3.3 · 10−7 and 6 · 10−8 at temperatures 78 and 15 K, respectively. Values of tan δ were also measured in liquid nitrogen and helium, and were found to be 1.1 · 10−4 and 5 · 10−6, respectively. The error in the measurement of tan δ does not exceed 15%.
Limiting Debye temperatures of hydrogen isotopes
Authors: Bereznyak N. G. , Sheinina A. A.
Published: January 2025

The empirical law of corresponding states is derived for limiting Debye temperatures (Θ00) of cryocrystals at T=0 and P=0 and used for obtaining consistent values of Θ00 for all molecular modifications of hydrogen isotopes. A method of determining Θ00 for hydrogen isotopes of various orth-para compositions is proposed.
Diamagnetic response of multi-layered superconducting Mo-Si films
Authors: Grishin A. M. , Drobot’ko V. F. , Khokhlov V. A. , Fedorenko A. I. , Yulin A.
Published: January 2025

Diamagnetic response of a thin film of superconducting Mo-Si superlattices was studied at 10 kHz as a function of the exciting field Hac = 5 · 10−4 –1 Oe and of the transport current jt− = 0–6 · 103 A/cm2. It is established that, as Hac is raised to 0.1 Oe, the diamagnetic response of Mo-Si superlattices is linear. However, even with further increase of the exciting field up to 0.7 Oe the critical state does not set in in the film. The diamagnetic signal spectrum, along with odd harmonics, reveals higher even harmonics. These experimental data are compared with diamagnetic susceptibilities of thin superconducting YBaCuO films.
On the angular dependence of the amplitude of quantum oscillations of the velocity of sound in metals with local anomalies of the Fermi surface curvature
Authors: Zimbovskaya N. A.
Published: January 2025

The effect of anomalies of the curvature of Fermi surface at its extremal cross-sections on the amplitude of quantum oscillations of the ultrasound velocity is considered. It is shown that these anomalies lead to a characteristic dependence of the oscillation amplitude on the direction of the external magnetic field. The nature of this dependence is analyzed.
Effect of an external field on the thermodynamics of the free-fermion model
Authors: Rutkevich S. B.
Published: January 2025

The effect of an external field on the phase transition is studied in the continuous version of the model of free fermions without dislocations. The critical indices δ = ∞, β = + 0, γ = 3/2 and the phase diagram are obtained as well as an exact expression for the free energy in the strong field limit. The results are compared with scaling properties in the six-vertex model. While the similarity of scaling in zero field and a coincidence of the values of β and δ indicate that both models have the same class of universality, considerable differences are observed in other characteristics like the index γ, phase diagram, and scaling function. This “discrepancy” is explained by the fact that the external field violates the symmetry in fermion and six-vertex models in different ways. The possibility of experimental observation of the obtained scaling dependences in two-dimensional crystals undergoing a transition to the incommensurate phase is discussed.
Enhancement of electromagnetic oscillations in bismuth by heat flux
Authors: Zhilyaev I. N.
Published: January 2025

The passage of heat flux through perfect single crystals of bismuth in a transverse magnetic field at liquid helium temperatures leads to an amplification of electromagnetic oscillations excited near the end-face of sample. This phenomenon is explained on the basis of Azbel’s instability model.
Photoinduced phenomena in HTS films of YBa2Cu3O6+δ
Authors: Dmitriev V. M. , Eremenko V. V. , Piryatinskaya V. G. , Prikhod’ko O. R. , Khristenko E. V.
Published: January 2025

The variation of spectral and current-carrying properties of YBa2Cu3O6+δ epitaxial films with different oxygen indices δ upon exposure to light is considered. It is shown that in the range 0.5 < δ < 0.75, illumination causes a decrease in the resistance and certain changes in the optical absorption spectrum which are equivalent to an increase in the oxygen content. It is also shown that even for δ > 0.75, illumination leads to a variation of the current-carrying characteristics of the films by changing the critical current density, while the temperature dependence of the resistance practically remains unchanged.
Luminescence quenching dynamics of ceramic YBa2Cu3O7−δ near the superconducting transition
Authors: Sushii V. N. , Nelipovich K. I. , Moiseev D. P. , Kuvaev V. N.
Published: January 2025

We studied photoluminescence spectra of the superconducting YBa2Cu3O7−δ ceramic within the range of wavelengths λ = 390 to 590 nm and the temperature range T = 80 to 120 K with a simultaneous recording of electrical resistivities near the transition to the superconducting state. A correlation has been established for the first time between the sensitivity of the temperature dependence of the radiation spectrum to the superconducting transition and the luminescence quenching dynamics. It is concluded that the superconducting properties of the YBa2Cu4O−δ surface can change under the action of the ultra-violet irradiation, which promotes removal of oxygen from the sample surface.
Localization in a “kinetic well” and infinite motion of a conduction electron in a crystal with edge dislocation
Authors: Dubrovskiĭ I. M.
Published: January 2025

The conduction electron is treated as a classical particle with an effective mass which is a function of the deformation field produced by an edge dislocation in a crystal. The analysis is confined to the simplest case of an isotropic crystal with the Poisson constant equal to 1/2 when the dilatation and the deformation potential proportional to it are equal to zero. It is shown that for a large constant of interaction with shear deformation, the electron may have a negative energy in a certain region near the dislocation and can move along a complex trajectory, which is finite in two dimensions and cannot be reduced to small oscillations under any initial conditions. For positive energy values, the motion of the electron is always infinite.
Specific heat peculiarities of the layered ferroelectric superconductor TIInS2
Authors: Gadzhiev B. R. , Mamedov N. T. , Godzhaev F. B.
Published: January 2025

A Landau-type theory of homogeneous-nonhomogeneous-homogeneous phase transition is constructed for layered systems with coexisting ferroelectric-antiferroelectric ordering. The values of specific heat index (degree of temperature dependence) have been determined for homogeneous phases (α = 2/3), the inhomogeneous phase near the homogeneous-nonhomogeneous (α = 0) and nonhomogeneous-homogeneous phase transitions (α = 1). The obtained theoretical results are compared with the experimental data on layered TlInS2 crystals.
Coupled electromagnetic and acoustic waves in metals with quasilocal electron states in a magnetic field
Authors: Ermolaev A. M. , Shurduk A. I.
Published: January 2025

The coupling of transverse electromagnetic and acoustic waves in metals with quasilocal electron states is considered. It is shown that the interaction between circularly polarized waves with plus polarization (antihelicons) and sound leads to the formation of coupled waves and to their mutual transformation. The spectrum and damping factor of coupled waves are calculated.
AC resistance of HTSC single crystals in the normal state
Authors: Dmitriev V. M. , Ofitserov M. N. , Prentslau N. N. , Demirskii V. V. , Rogacki K. , Sadowski W.
Published: January 2025

It is found that HTSC single crystals share a common feature with ceramics–a change of the sign of the slope in the temperature dependence of the ohmic resistance at certain frequencies, when the sign at direct current is positive. This feature was investigated on Y-, Er- and Dy-based single crystals. The frequency, at which ohmic resistance becomes temperature-independent, is found to correlate with the dc transport properties.
H–T phase diagram of erbium orthochromite. Magnetoacoustic measurements
Authors: Tsymbal L. T. , Izotov A. I.
Published: January 2025

In this paper, the results of the first ultraviolet investigations of the dynamics of orientational phase transitions in an ErCrO3 single crystal are presented. The data obtained from magnetoacoustic investigations are used to construct the H–T phase diagram of erbium orthochromite, whose details differ from the previously known diagram. The nature of the observed phase transitions is investigated.
Nonlinear irreversible rf impedance of granular YBaCuO films
Authors: D’yachenko A. I. , Chabanov V. V.
Published: January 2025

The properties of YBaCuO films are studied in the critical state at frequencies between 10 and 20 MHz in a parallel external magnetic field. The anomalous hysteresis phenomena and the effect of rf magnetic field and wave frequency on impedance components are investigated. The measured data are in qualitative agreement with those for metal ceramic plates. However, there is a significant quantitative difference between the effects of variable and static field amplitudes on impedance in plates and in films. The effect is about two-three orders of magnitude higher in films. The results are analyzed in terms of the critical state model for a thin-film geometry with a parallel varying field.
Superposition of strain-hardening mechanisms in Al–Li alloys at low temperatures
Authors: Isaev N. V. , Fomenko V. S.
Published: January 2025

Measurement of the rate sensitivity of the deforming stress and an analysis of the obtained experimental data by the theory of thermally activated plasticity are used to study the effect of doping and aging on the physical mechanisms determining the mechanical properties of Al–Li alloys at low temperatures.
Electical resistance of NbSe3 single crystals under axial pressure
Authors: Chashka Kh. B. , Veletskii V. I. , Obolenskii M. A.
Published: January 2025

The effect of axial pressure applied perpendicularly to the high-conductivity axis on the electrical resistance of niobium triselenide (NbSe3) single crystals is studied experimentally. An increase in pressure elevates the superconducting transition temperature. The temperature of CDW transition at 59 K also increases simultaneously. It is shown that both effects can be described qualitatively by using the concept of Peierls gap suppression at 59 K upon an increase in axial pressure for the given geometry.
On the melting curve of a vortex lattice in high-temperature superconductors
Authors: Babich I. M. , Mikitik G. P. , Sharlai Yu. V.
Published: January 2025

An analytic expression describing the melting curve of a vortex lattice in high-temperature superconductors is derived. The theory is compared with the available experimental data.
Thermal activation in underdamped physical systems: The supercurrent decay of Josephson junctions
Authors: Ruggiero B. , Silvestrini P.
Published: January 2025

We have performed measurements on the supercurrent decay of Josephson tunnel junctions at temperature ranging between 1.27 and 4.2 K in order to investigate the thermal activation theory. From the theoretical point of view we modified the RSJ model taking into account the dependence on voltage and temperature of the quasiparticle tunneling. The very good agreement of data with theory confirms the correctness of our assumptions and allows the experimental investigation of the general thermal activation theory in the crossover region between the extremely underdamped regime and the moderately underdamped one.
Natural vibrational spectrum and Green’s functions of magnets with complete spontaneous symmetry breaking
Authors: Kovalevskii M. Yu. , Rozhkov A. A.
Published: January 2025

The hydro- and thermodynamics of magnets with completely broken symmetry are constructed by using the Fermi-liquid approach. The spectra of free oscillations are obtained and analyzed in the presence and in the absence of an external magnetic field. Low-frequency asymptotic forms of Green’s function in a uniform external magnetic field are calculated. The singularities of basis Green’s functions are considered.
Effect of plastic deformation on transport properties of composites Bi (2212)-Ag
Authors: Dolgin A. M. , Kislyak I. F. , Dotsenko V. I. , Demirskaya O. V. , Ishchuk V. M. , Seminozhenko V. P.
Published: January 2025

The effect of elastic and plastic (up to 50%) deformation on the current-carrying capacity of a composite in the form of a silver wire coated with an HTS bismuth ceramic film (2212 phase) is studied. It is found that the composite ensures the passage of superconducting current under a strain up to 30%. A model proposed for describing the degradation of the transport current in composites provides a satisfactory quantitative explanation of the observed effect over a wide range of strains.
Ni2+–Ni2+ exchange interaction in the high-pressure phase of MgSiF6·6H2O crystal
Authors: Krygin I. M. , Prokhorov A. D.
Published: January 2025

The spin-spin interaction between pairs of paramagnetic ions of bivalent nickel is studied experimentally in MgSiF6 · 6H2O single crystals in the high-pressure phase (R3) at a frequency of 36 GHz at 4.2 K. It is shown that the electron paramagnetic resonance spectrum belongs to the nearest pair of Ni ions. The interaction is described by the term S1K^S2 of the spin Hamiltonian. The components of the tensor K^ include isotropic exchange and magnetic dipole-dipole interactions. It is found that the exchange interaction in the phase under investigation is of the ferromagnetic type and increases linearly with pressure: J = – 580–22P.