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E. Yu. Beliayev

Publications and source records attributed to E. Yu. Beliayev.

At least 19 recordsLinked to original sources
arXiv2026

Low-Temperature Magnetoresistance Hysteresis in Granular Cr1-xFexO2: Slow Relaxation of Transport-Active Magnetic Configurations

Low-temperature magnetoresistance loops of compacted CrO2 powders become strongly nonmonotonic when electrical transport is dominated by a small number of spin-dependent intergranular tunnelling paths. We reanalyse previously reported data for undoped CrO2 and Fe-containing Cr1-xFexO2, focusing on additional branch crossings beyond the conventional low-field hysteresis. In the Fe-containing specimen, the resistance decreases, passes through a minimum, rises over an extended field interval, and then decreases again at higher field. This nonmonotonic hysteretic feature is strongly reduced when the magnetic-field sweep is slowed. Digitization of the three fastest sweeps shows that the field at which the resistance starts to recover shifts approximately linearly with sweep rate, corresponding to an effective magnetotransport relaxation time of about 3 s. This scale is attributed not to microscopic spin flips but to the slow evolution of local moment and domain configurations at the intergranular contacts dominating the current. The observations are consistent with conventional negative tunnelling magnetoresistance superimposed on a slower resistance-increasing contribution associated with transient local magnetic disorder. Fe increases coercivity and interfacial magnetic heterogeneity while reducing the overall negative magnetoresistance. The results support a transport-weighted magnetic-reconfiguration mechanism for the unusual hysteresis shape.

cond-mat.dis-nn↗
arXiv2026

Transport-Weighted Coercivity in Granular CrO2: Why Magnetoresistance and Magnetization Can Disagree

Magnetoresistance hysteresis is often used to estimate the coercive field of a magnetic material. We reanalyse our published magnetotransport and magnetometry data on compacted powders of the half-metallic ferromagnet CrO2 and show that this identification can fail in a granular conductor. The field Hp at the resistance maximum may be close to, above, or below the bulk coercive field Hc, depending on temperature and measuring current. For three samples with different particle shapes and insulating-shell thicknesses, the digitized ratio Hp/Hc follows the same qualitative sequence and suggests a common crossover near 15 K. We interpret this behaviour as a change in which interparticle junctions control the electrical response. Bulk magnetometry averages over the entire magnetic volume, whereas tunnelling resistance gives the largest weight to the small set of links that carries the current. Cohn's exact network-sensitivity theorem provides a rigorous linear-response definition of these transport weights. In simple terms, Cohn showed that the influence of a given contact on the total resistance is proportional to the square of the current flowing through that contact. Combined with known magnetic pair-correlation effects, this leads to the concept of transport-weighted coercivity. In granular sensors and spin-dependent composites, the resistance peak cannot automatically be treated as the bulk coercive field. Conversely, the difference Hp - Hc may serve as a diagnostic of current-path localization, barrier evolution, and device-to-device variability.

cond-mat.dis-nn↗
arXiv2026

Vertically Correlated Disorder and Structured Interlayer Tunneling in Cuprates

Cuprate superconductors display robust in-plane electronic correlations but exceptionally fragile interlayer coherence. We suggest that even weak vertically correlated disorder (arising from interstitial-oxygen staging, twin boundaries, extended strain fields, or defect-pinned charge textures) can impose a layer-dependent modulation of the interlayer tunneling amplitude t(z). Because the bare interlayer coupling is intrinsically small, such modulations generate an effectively multichannel c-axis electrodynamic response, consistent with multi-component Josephson plasma resonances, nonmonotonic c-axis resistivity, redistribution of bilayer magnetic spectral weight, and field-enhanced vertical CDW correlations. We propose a phenomenological framework in which the organization of disorder, rather than its magnitude, governs the effective interlayer coupling and its electrodynamic signatures. This viewpoint unifies diverse c-axis anomalies across several cuprate families, suggesting that controlling vertical disorder correlations offers a viable pathway for tuning dimensionality and interlayer coherence in high-Tc superconductors.

cond-mat.supr-con↗
arXiv2026

Emergent Coherence at the Edge of Magnetism: Low-Doped La2-xSrxCuO4+delta Revisited

The La2-xSrxCuO4+delta (LSCO) system provides a unique experimental setting for exploring how magnetism, superconductivity, and disorder jointly shape charge transport in a doped Mott insulator. Transport measurements in lightly doped and oxygen-enriched LSCO reveal a strongly insulating normal state governed by variable-range hopping, accompanied by pronounced nonlinear current-voltage characteristics and, at low temperatures, current-induced negative differential resistance. With increasing carrier concentration, these features evolve into regimes characterized by granular and percolative superconductivity near the threshold of bulk superconductivity and, eventually, into a homogeneous strange-metal state close to optimal doping. Throughout this evolution, the transport response shows marked sensitivity to disorder, electronic inhomogeneity, and external control parameters, such as bias current and magnetic field. Rather than reflecting a sequence of sharply distinct phases, the observed transport regimes form a continuous crossover from a localization-dominated insulating state to granular superconductivity and further to a coherent metallic state. This crossover is driven primarily by the progressive enhancement of electronic screening, inter-region coupling, and superconducting connectivity, rather than by abrupt changes in the underlying microscopic scattering mechanisms. Taken together, the available transport data provide a coherent experimental basis for understanding how disorder and mesoscale electronic inhomogeneity organize charge transport and superconductivity across the LSCO phase diagram, underscoring the central role of percolation and nonequilibrium effects in underdoped cuprates.

cond-mat.str-el↗
arXiv2025

Superconductivity in La1.85Sr0.15CuO4 Ceramic Samples

Effects related to the granularity of a La1.85Sr0.15CuO4 ceramic sample, synthesized by the solidstate reaction method, are presented. The superconducting transition exhibits a step-like behavior. Lowtemperature features of magnetoresistance hysteresis loops associated with the granular structure of the sample have been observed.

cond-mat.supr-con↗
arXiv2025

Electron Transport in Compacted Powders of VO2 Nanoparticles: Variable Range Hopping vs Percolation Behavior

Electron transport properties in compacted VO2 nanopowders were studied. While VO2 usually exhibits a first-order metal-insulator transition (MIT) at ~340K, in our compressed nanopowder samples the MIT was significantly broadened due to structural disorder, interparticle barriers, and phase coexistence. Resistivity measurements in the temperature range of 78 - 682 K initially suggested a variable range hopping (VRH) transport mechanism, but further analysis indicates that the observed temperature dependence is governed by percolative conductivity, modified by activation-assisted tunneling effects. Suppression of the expected resistance jump at the MIT is attributed to dynamic intergranular barrier restructuring, residual localized states, and percolative electron transport. These findings highlight the necessity of considering percolation effects when analyzing transport mechanisms in granular VO2-based systems.

cond-mat.str-el↗
arXiv2025

Changes in the coercivity fields of magnetoresistance hysteresis loops under the influence of a spin-polarized current

Using the example of a pressed sample consisting of chromium dioxide nanoparticles coated with insulating shells, we study the relationship between the electronic transport system and magnetic subsystem in granular spin-polarized metals. It is shown that the spin-polarized tunneling transport current can affect the coercivity fields of the percolation cluster formed in the sample with decreasing temperature.

cond-mat.mes-hall↗
arXiv2022

Coalescence of Impurity Strontium Atoms in Lightly-Substituted Samples of Lanthanum Cuprate

By comparing experimental results obtained in the study of the electron transport and magnetic properties of samples of lightly strontium-substituted lanthanum cuprates and the results of a previously published numerical analysis in the reduced elastic scattering space (RPS) of the elastic scattering cross-section, we construct a phenomenological classical self-consistent strong-binding energy density profile in the superconducting $La_{2-x}Sr_xCuO_4$ cuprate. It is found that the imaginary part of the reduced phase scattering space can be zero, almost constant, or strongly self-consistent, depending on the Sr substituted concentration. If the Sr atomic concentration is dilute, a constant imaginary part of the elastic scattering cross-section brings a sub-melted coalescent superconducting metallic profile similar to the one with a constant scattering lifetime in the metallic state of normal metals, except for the unitary narrow, sharp peak at zero frequency. A self-consistent broadening of this peak occurs for a higher concentration of Sr atoms, and finally, for very small amounts of nonmagnetic dirt, only the narrow unitary peak prevails around the zero frequency.

cond-mat.supr-con↗
arXiv2021

Dressed behavior of the quasiparticles lifetime in the unitary limit of two unconventional superconductors

We compare the quasiparticle lifetime behavior in the unitary limit of two unconventional superconductors dressed by non-magnetic impurity scattering to differentiate an anomalous functional behavior in its shape when the disorder concentration is changed in a triplet paired model with respect to the well behave singlet model. For singlet paired superconductors, the functional shape of the lifetime due to elastic scattering around the nodal regions does not change with the change of the disorder concentration, but for a triplet model with a tiny gap, an anomalous drop in shape is observed only when small values of disordering are added. We use a 2D tight-binding parametrization to study the reduced phase space of the first Brillouin zone, where the low energy scattering is restricted to the nodal/quasinodal regions for two irreducible representations of the crystal lattice.

cond-mat.supr-con↗
arXiv2020

Effect of Oxygen Saturation on AFM-WFM-HTSC Transition Temperatures in RuSr2(Eu1.5Ce0.5)Cu2O10-δ Ceramic Samples

The effect of annealing in high pressure oxygen atmosphere on superconducting transition temperatures for ceramic samples of magnetic superconductor europium based 1222 ruthenocuprate was studied. It was shown that the properties of the samples are consistent with the behavior of granular superconducting system. As a result of oxygen saturation the superconducting transition temperatures become higher. Particularly, the shift of superconducting transition temperature for the intergranular medium is 9.2 K and for the matter within the granules 6.8 K. This difference is supposed due to the mechanism of oxygen diffusion along the grain boundaries. In the temperature range between 135 K and 350 K the behavior of resistance obeyed the Mott law of variable range hopping for three dimensional case.

cond-mat.supr-con↗
arXiv2016

Features of Low Temperature Tunnel Magnetoresistance in Pressed Powder of Chromium Dioxide

Resistive and magnetoresistive properties of two samples of compacted powders of ferromagnetic half-metal CrO_{2} with shape anisotropy of nanoparticles were studied. The powders were prepared by the method of hydrothermal synthesis and consisted of needle-like particles with average diameters 24-34 nm and mean length of 300 nm. One of the samples has been made of compacted powder of pure CrO_{2}, while another sample has been prepared from a substitution solid solution Cr_{1-x}Fe_{x}O_{2}. The aim of this work was to study the effect of Fe impurity on the value of tunnel resistance and tunnel magnetoresistance for compacted CrO_{2} powders. It was found that the addition of Fe impurity leads to an increase in the coercive force of the powder and reduce the tunnel magnetoresistance. We assume resonant tunneling mechanism on the Fe impurities. We found a strong dependence of the magnetoresistance on the spin relaxation rate in the process of magnetization reversal. The possible reasons for such dependence are discussed.

cond-mat.mes-hall↗
arXiv2012

Resistive and magnetoresistive properties of CrO2 pressed powders with different types of inter-granular dielectric layers

Resistive, magnetoresistive and magnetic properties of four kinds of pressed CrO2 powders, synthesized by hydrothermal method of chromic anhydride have been investigated. The particles in powders constituted of rounded particles (diameter 120 nm) or needle-shaped crystals with an average diameter of 22.9 nm and average length of 302 nm. All of the particles had a surface dielectric shell of varying thickness and different types (such as oxyhydroxide -CrOOH or chromium oxide Cr2O3). For all the samples at low temperatures we found non-metallic temperature dependence of resistivity and giant negative magnetoresistance (MR). The maximum value of MR at low temperatures (T \approx 5 K) is \approx 37% in relatively small fields (0.5 T). At higher temperatures there was a rapid decrease of MR (up to \approx 1% / T at T \approx 200 K). The main objective of this work was studying the influence of properties and thickness of the intergranular dielectric layers, as well as CrO2 particle shape, on the magnitude of the tunneling resistance and MR of the pressed powder. The new results obtained in this study include: (1) detection at low temperatures in powders with needle-like particles a new type of MR hysteresis, and nonmonotonic MR behaviour with increasing magnetic field (absolute value of the MR at first grows rather rapidly with the field, and then begins diminishing markedly, forming a maximum), and (2) detection of non-monotonic temperature dependence, where - a field in which the resistance in a magnetic field has a maximum, as well as finding discrepancies in values of and coercivity fields, (3) detection of the anisotropy of MR, depending on the relative orientation of the transport current and the magnetic field, (4) a new method of synthesis, to regulate the thickness of dielectric coating.

cond-mat.str-el↗
arXiv2012

Hysteresis and stepwise structure in MR curves of granular superconducting ruthenocuprates RuSr$_2$(Gd$_{1.5}$Ce$_{0.5})$Cu$_2$O$_{10-δ}$}

Granular superconductivity effects in a polycrystalline sample of ruthenocuprate RuSr$_2$(Gd$_{1.5}$Ce$_{0.5})$Cu$_2$O$_{10-δ}$ are studied. The main attention has been devoted to manifestation of these effects in current and magnetic-field dependences of resistive transition to superconducting state. It is found that current dependences of differential resistance taken at different temperatures intersect strictly at two definite values of current demonstrating crossing point effect. This phenomenon has been explained taking into account inhomogeneous state of intergrain medium which can be considered as a two-component system. The particular attention has been given to magnetoresistance (MR) hysteresis in mixed state of this inhomogeneous system and to influence of applied current and temperature on this phenomenon. Two types of hysteresis (clockwise and anticlockwise) have been found with transition from clockwise to anticlockwise hysteresis with increasing temperature. Stepwise structure in MR hysteretic curves has been observed in low-field range. Possible reasons of the change in hysteresis behavior with increasing temperature and appearance of the stepwise structure in MR curves are discussed taking into consideration inhomogeneous state of the granular superconductor studied.

cond-mat.supr-con↗
arXiv2011

Mixed (1D-2D) quantum electron transport in percolating gold film

The gold film (mean thickness $\approx$ 3.5 nm) was condensed in high vacuum at temperature 70 K on single-crystal sapphire substrate. The transport properties of the film at low temperature reveal simultaneously indications of 1D and 2D quantum interference effects of weak localization and electron-electron interaction. It is shown that this behavior is determined by inhomogeneous electron transport at the threshold of thickness-controlled metal-insulator transition.

cond-mat.mes-hall↗
arXiv2010

Anomalies of conductivity behavior near the paramagnetic-antiferromagnetic transition in single-crystals La_{2}CuO_{4+δ}

The temperature dependences of resistance, R(T), of two single-crystals La_{2}CuO_{4+δ} samples have been studied with the aim to detect a possible change in the R(T) behavior induced by paramagnetic-antiferromagnetic (PM-AFM) transition. One of the samples with δ\lesssim 0.01, was fairly homogeneous in oxygen distribution (not phase-separated) with Neel temperature T_{N}\approx 266 K. Conductivity of this sample has been determined by Mott's variable-range hopping below T_N. The other, far less resistive, sample with δ\approx 0.05, was inhomogeneous (phase-separated) showing both PM-AFM (T_N\approx 205 K) and superconducting (T_c\approx 25 K) transitions. It is found that for the homogeneous sample the resistivity decreases above T_N far faster with temperature than below it (for both directions of measuring current, parallel and perpendicular to basal CuO_2 planes). A similar behavior of conductivity near PM-AFM transition is also found for the phase-separated and less resistive sample. In this case a clear kink in R(T) curve near T_N\approx 205 K can be seen. Furthermore, a transition to metallic (dR/dT>0) behavior occurs far enough above T_N. The observed behavior of the samples studied is related to increased delocalization of charge carriers above T_N. This is in accordance with decrease in the AFM correlation length and corresponding enhancement of the hole mobility above T_N known for low-doped lanthanum cuprates.

cond-mat.mtrl-sci↗
arXiv2009

Transport and magnetotransport properties of cold-pressed CrO$_2$ powder, prepared by hydrothermal synthesis

Submicron powder of CrO$_2$ was prepared by hydrothermal synthesis method from chromium trioxide. Particles obtained were of rounded form with mean diameter about 120 nm. The powder (stabilized with thin surface layer of β-CrOOH) has been characterized by structural, X-ray and magnetic measurements. The powder (with Curie temperature about 385 K) was cold-pressed and its transport and magnetotransport properties have been measured in the temperature range 4--450 K in magnetic field up to 1.6 T. The samples studied is characterized by non-metallic temperature behavior of resistance and large negative magnetoresistance (MR) in low temperature range. At T=5 K the MR magnitude has been -17% at H=0.3 T and -20% at H=1.4 T. Its magnitude decreased fast with increase in temperature reducing to 0.3% and less for T>200 K. It is shown that this MR behavior is inherent for a system of magnetic grains with spin-dependent intergrain tunnelling. Some peculiarities of MR behavior in low-temperature range (below 40 K) can be associated with percolating character of tunnelling conductivity of this granular system under conditions of availability of only few conducting current paths through the sample.

cond-mat.mtrl-sci↗
arXiv2008

The effect of magnetic (phase) inhomogeneities upon the low temperature conductivity of antiferromagnetic La_{2}CuO_{4+δ} single crystal

It is found that a strong inhomogeneous distribution of oxygen in single crystal La_{2}CuO_{4+δ} can lead to the formation of isolated superconducting inclusions, the average hole concentration being no more than 0.0024 per Cu atom. The behavior of the conductivity in the magnetic field below T=20 K is consistent with possible existence of a insulating low-temperature magnetic phase (spin density waves), which is typical of cuprates with excess oxygen.

cond-mat.supr-con↗