arXiv subjects

A. V. Terekhov

Publications and source records attributed to A. V. Terekhov.

18 recordsLinked to original sources

arXiv2026

Specific features of the magnetic-field dependences of electrical resistivity in Bi--Mn solid solutions with low Mn content

For the first time, the field dependences of the magnetoresistance of a textured polycrystalline Bi$_{88.08}$Mn$_{11.92}$ sample were investigated in the $H \perp I$ and $H \parallel I$ configurations, and the results were compared with those previously obtained for the solid solution Bi$_{95.69}$Mn$_{3.69}$Fe$_{0.62}$ with a lower manganese concentration. It was demonstrated that the magnetoresistance field dependencies for Bi$_{88.08}$Mn$_{11.92}$ differ significantly from those of Bi$_{95.69}$Mn$_{3.69}$Fe$_{0.62}$ below 100 K, becoming nearly identical as the temperature approaches room temperature. It was established that the maximum relative magnetoresistance values for Bi$_{88.08}$Mn$_{11.92}$ are observed at a magnetic field of 90 kOe and a temperature of 100 K in both the $H \perp I$ and $H \parallel I$ configurations, amounting to 3170\% and 380\%, respectively. These values are significantly lower than those previously reported for the solid solution containing less manganese (Bi$_{95.69}$Mn$_{3.69}$Fe$_{0.62}$), which were 3877\% and 742\%, respectively. Analysis of the results indicates that differences in field dependence among the studied materials are associated with varying amounts of magnetic $α$-BiMn. The anomalous magnetoresistance behavior, as compared with that of pure bismuth, is attributed to the influence of internal magnetism on electrical transport within the bismuth matrix of the studied solid solutions.

cond-mat.mtrl-sci↗

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

Effect of a magnetic field up to 9 T on the temperature dependence of the pseudogap in YBa$_2$Cu$_3$O$_{7-δ}$ films

The work analyzes the effect of a magnetic field $B$ directed along the $c$ axis ($B \parallel c$) up to 9~T on the resistivity $ρ(T)$, fluctuation conductivity (FLC) $σ'(T)$ and pseudogap $Δ^*(T)$ in thin films of YBa$_2$Cu$_3$O$_{7-δ}$ with a critical temperature of the superconducting transition $T_c = 88.8$~K. In contrast to previous work, where the magnetic field was directed along the $ab$ plane ($B \parallel ab$), the influence of the field on the sample is stronger due to the contribution of both spin--orbit and Zeeman effects. It was found that the BEC--BCS transition temperature, $T_{\mathrm{pair}}$, which corresponds to the maximum of the $Δ^*(T)$ dependence, shifts to the region of lower temperatures with increasing $B$, and the maximum value of $Δ^*(T_{\mathrm{pair}})$ decreases in fields $B > 5$~T. It was found that with increasing field, the low-temperature maximum near $T_0$ is smeared and disappears at $B > 1$~T. In addition, above the Ginzburg temperature $T_G$, for $B > 1$~T, a minimum appears on $Δ^*(T)$ at $T_{\min}$, which becomes very pronounced with a subsequent increase in $B$. As a result, the overall value of $Δ^*(T_G)$ decreases noticeably, most likely due to the pair-breaking effect. At the same time, $ΔT_{\mathrm{fl}}$ and $ξ_c(0)$ increase sharply by approximately 3 times with increasing $B$ above 1~T. Our results confirm the possibility of the formation of a vortex state in YBa$_2$Cu$_3$O$_{7-δ}$ by a magnetic field and its evolution with increasing $B$.

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↗

arXiv2025

Anomalous behaviour of the temperature dependencies of the upper critical fields in (Dy1-xErx)Rh3.8Ru0.2B4 (x=0, 0.2, 0.4)

For the first time, a detailed analysis of the behaviour of the temperature dependences of the upper critical fields Hc2(T) has been carried out in the compounds (Dy1-xErx)Rh3.8Ru0.2B4 (x = 0, 0.2, 0.4). It is found that the Hc2(T) in (Dy0.8Er0.2)Rh3.8Ru0.2B4 has an inflection point at 3 kOe, which may be related to the low-temperature magnetic ordering, while a more exotic mechanism caused by the transition from ordinary singlet to triplet superconductivity is not excluded. For the first time, the experimental Hc2(T) dependences of (Dy1-xErx)Rh3.8Ru0.2B4 (x = 0, 0.2, 0.4) compounds have been fitted within the framework of Werthamer-Helfand-Hohenberg theory (WHH) with the Maki parameter alpha > 0, indicating that spin-paramagnetic effects due to magnetic exchange interactions play an essential role in suppressing superconductivity in these compounds.

cond-mat.supr-con↗

arXiv2024

Evolution of the pseudogap temperature dependence in YBa$_2$Cu$_3$O$_{7-δ}$ films under the influence of a magnetic field

The evolution of the temperature dependence of pseudogap $Δ$*(T) in optimally doped (OD) YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) films with $T_{c}$ = 88.7 K under the influence of a magnetic field $B$ up to 8 T has been studied in detail. It has been established that the shape of $Δ$*(T) for various $B$ over the entire range from the pseudogap opening temperature $T$* to $T_{01}$, below which superconducting fluctuations occur, has a wide maximum at the BEC-BCS crossover temperature $T_{pair}$, which is typical for OD films and untwinned YBCO single crystals. $T$* was shown to be independent on $B$, whereas $T_{pair}$ shifts to the low temperature region along with increase of $B$, while the maximum value of $Δ$*($T_{pair}$) remains practically constant regardless of $B$. It was revealed that as the field increases, the low-temperature maximum near the 3D-2D transition temperature $T_{0}$ is blurred and disappears at $B$ > 5 T. Moreover, above the Ginzburg temperature $T_{G}$, which limits superconducting fluctuations from below, at $B$ > 0.5 T, a minimum appears on $Δ$*(T) at $T_{min}$, which becomes very pronounced with a further increase in the field. As a result, the overall value of $Δ$*(T) decreases noticeably most likely due to pair-breaking affect of a magnetic field. A comparison of $Δ$*(T) near $T_{c}$ with the Peters-Bauer theory shows that the density of fluctuating Cooper pairs actually decreases from < > $\approx$ 0.31 at $B$ = 0 to < > $\approx$ 0.28 in the field 8 T. The observed behavior of $Δ$*(T) around $T_{min}$ is assumed to be due to the influence of a two-dimensional vortex lattice created by the magnetic field, which prevents the formation of fluctuating Cooper pairs near $T_{c}$.

cond-mat.supr-con↗

arXiv2022

Temperature dependence of upper critical fields and coherence lengths for optimally-doped $YBa_2Cu_3O_{7-δ}$ thin films

We report the comprehensive comparative analysis of the upper critical magnetic fields $μ_{0}H_{c2}(0)$ obtained within Ginzburg-Landau and Werthamer-Helfand-Hohenberg theories for optimally-doped $YBa_2Cu_3O_{7-δ}$ thin films. For different orientations of the magnetic field, our calculations give 638 and 153 T for $μ_{0}H_{c2}(0)$, H || ab and $μ_{0}H_{c2}(0)$, H || c, respectively, when using $H_{c2}(0)$. For the first time, the temperature dependences of coherence lengths $ξ_{ab}(T)$ and $ξ_{c}(T)$ within proposed theories were determined using 50 and 90% criteria of the normal state resistivity value $ρ_{N}$. The Ginzburg-Landau 0.9$ρ_{N}$ approach gives $ξ_{ab}(0)$=11.8 A, and $ξ_{c}(0)$=3.0 A which are in a good agreement with literature data. The implications of very short coherence lengths in HTSCs are discussed.

cond-mat.supr-con↗

arXiv2021

Features of Excess Conductivity Behavior in a Magnetic Superconductor Dy$_{0.6}$Y$_{0.4}$Rh$_{3.85}$Ru$_{0.15}$B$_4$

The temperature dependencies of the excess conductivity $σ'(T)$ and possible pseudogap (PG), in a Dy$_{0.6}$Y$_{0.4}$Rh$_{3.85}$Ru$_{0.15}$B$_4$ polycrystal were studied for the first time. It was shown that $σ'(T)$ near T$_{c}$ is well described by the Aslamazov Larkin fluctuation theory, demonstrating a crossover with increasing temperature. Using the crossover temperature $T_0$, the coherence length along the c axis $ξ_c(0)$, was determined. Above the level of $T_{2D}>T_{0}$, an unusual dependence $σ'(T)$ was found, which is not described by the fluctuation theories in the range from $T_{0}$ to $T_{FM}$, at which a ferromagnetic transition occurs. The range in which superconducting fluctuations exist is apparently quite narrow and amounts to $ΔT_{fl}=2.8 K$. The resulting temperature dependence of the PG parameter $Δ^*(T)$ has the form typical of magnetic superconductors with features at $T_{max}=154 K$ and the temperature of a possible structural transition at $T_{s}=95 K$. Below $T_{s}$, dependence $Δ^*{T}$ has a shape typical for PG in cuprates, which suggests that the PG state can be realized in Dy$_{0.6}$Y$_{0.4}$Rh$_{3.85}$Ru$_{0.15}$B$_4$ in this temperature range. Comparison of $Δ^*(T)$ with the Peters Bauer theory made it possible to determine the density of local pairs ~0.35, near T$_{c}$, which is 1.17 times greater than in optimally doped YBa$_{2}$Cu$_{3}$O$_{7-δ}$ single crystals.

cond-mat.supr-con↗

arXiv2019

Effect of rf electromagnetic irradiation on current-voltage characteristics of wide superconducting films

The effect of the electromagnetic irradiation on the current-voltage characteristics (IVCs) of a wide superconducting film is experimentally investigated. In contrast to the microwave field (several GHz) which suppresses vortex resistivity, the action of the rf field (tens of MHz) leads to significant expansion of the linear part of the IVC due to rapid suppression of the critical current with a slower change in the upper stability limit of the vortex state where the phase-slip lines (PSLs) occur. With an increase in the rf power, the stepwise structure of the IVC associated with the PSLs becomes smoothed and eventually disappears. A model of the IVC in the adiabatic regime is proposed, which explains the effects of smoothing of the voltage steps and the suppression of the critical current.

cond-mat.supr-con↗

arXiv2017

Electron-Phonon Interaction in Ternary Rare-Earth Copper Antimonides LaCuSb2 and La(Cu0.8Ag0.2)Sb2 probed by Yanson Point-Contact Spectroscopy

Investigation of the electron-phonon interaction (EPI) in LaCuSb2 and La(Cu0.8Ag0.2)Sb2 compounds by Yanson point-contact spectroscopy (PCS) has been carried out. Point-contact spectra display a pronounced broad maximum in the range of 10÷20 mV caused by EPI. Variation of the position of this maximum is likely connected with anisotropic phonon spectrum in these layered compounds. The absence of phonon features after the main maximum allows the assessment of the Debye energy of about 40 meV. The EPI constant for the LaCuSb2 compound was estimated to be λ=0.2+/-0.03. A zero-bias minimum in differential resistance for the latter compound is observed for some point contacts, which vanishes at about 6 K, pointing to the formation of superconducting phase under point contact, while superconducting critical temperature of the bulk sample is only 1K.

cond-mat.supr-con↗

arXiv2015

Anisotropy of electric resistance and upper critical field in magnetic superconductor Dy$_{0.6}$Y$_{0.4}$Rh$_{3.85}$Ru$_{0.15}$B$_4$

We have measured temperature dependencies of the electric resistance $R$ and upper critical magnetic field $H_{c2}$ of a magnetic superconductor Dy$_{0.6}$Y$_{0.4}$Rh$_{3.85}$Ru$_{0.15}$B$_4$. The measurements were made for different angles $φ$ of magnetic field inclination to the direction of measuring current and revealed strong anisotropy of the behavior of $R(T)$ and the values of $H_{c2}(T)$. By using the Werthamer-Gelfand-Hohenberg theory, we determined the Maki parameter $α$ and the parameter of the spin-orbital interaction. For $φ= 0^\circ$ and $90^\circ$ both parameters are close to zero, thus the magnitude of $H_{c2}(0) \approx 38$ kOe is basically limited by the orbital effect. At $φ= 45^\circ$, a large value of the parameter $α= 4.2$ indicates dominating role of the spin-paramagnetic effect in the suppression of $H_{c2}(0)$ down to $8.8$ kOe. We suggest that such behavior of $R(T)$ and $H_{c2}(T)$ is caused by internal magnetism of the Dy atoms which may strongly depend on the magnetic field orientation.

cond-mat.supr-con↗

arXiv2015

Fluctuation conductivity and possible pseudogap state in FeAs-based superconductor EuFeAsO(0.85)F(0.15)

The study of excess conductivity $σ'(T)$ in the textured polycrystalline FeAs-based superconductor $EuFeAsO_{0.85}F_{0.15}$ ($T_c = 11\, K$) prepared by the solid state synthesis is reported. The $σ'(T)$ analysis has been performed within the Local Pair (LP) model based on the assumption of the LP formation in cuprate high-$T_c$ superconductors (cuprates) below the pseudogap (PG) temperature $T^*\gg T_c$. Similarly to the cuprates, near $T_c$ $σ'(T)$ is adequately described by the 3D term of the Aslamasov-Larkin (AL) theory but the range of the 3D-AL fluctuations, $ΔT_{3D}$, is relatively short. Above the crossover temperature $T_0 \approx 11.7\,K$ $σ'(T)$ is described by the 2D Maki-Thompson (MT) fluctuation term of the Hikami-Larkin (HL) theory. But enhanced 2D-MT fluctuation contribution, being typical for the magnetic superconductors, is observed. Within the LP model approach the PG parameter, $Δ^*(T)$, was determined for the first time. $Δ^*(T)$ shows the narrow maximum at $T_s \approx 160\,K$ followed by the linear drop down to $T_{SDW}=T_{NFe}\approx 133\,K$. Both small $ΔT_{3D}$ and enhanced $σ'(T)$, including linear $Δ^*(T)$ drop, are considered to be the evidence of the enhanced magnetic interaction in $EuFeAsO_{0.85}F_{0.15}$. Importantly, the slop of the linear $Δ^*(T)$ and its length are found to be the same as observed for $SmFeAsO_{0.85}$. The results suggest both the similarity of magnetic interaction processes in different Fe-pnictides and applicability of the LP model approach to the $σ'(T)$ analysis even in magnetic superconductors.

cond-mat.supr-con↗

arXiv2012

Increase of superconducting order parameter in the magnetic superconductor Dy0.6Y0.4Rh3.85Ru0.15B4 in a wide magnetic field range. Is it a further candidate in p-wave superconductors?

The Andreev reflection spectra were studied for the first time in the magnetic superconductor Dy0.6Y0.4Rh3.85Ru0.15B4. It is found that an external magnetic field (up to 0.7 Hc2) is a strong stimulator of superconductivity in contrast with traditional superconductors with a singlet pairing. The ratio 2Δ/kBTc \approx 4.0 obtained for some contacts is higher than the value 3.52 which is typical of conventional superconductors with a weak electron-phonon interaction. It has been proposed that in Dy0.6Y0.4Rh3.85Ru0.15B4 a triplet mechanism of superconducting pairing is realized.

cond-mat.supr-con↗

arXiv2010

Andreev reflection spectroscopy of the new Fe-based superconductor EuAsFeO0.85F0.15: evidence for the strong order parameter anisotropy

Andreev reflection spectra have been measured in a new superconductor EuAsFeO0.85F0.15 having an unexpectedly low superconducting transition temperature Tc~11.3 K among related FeAs compounds on a base Sm and Gd surrounding Eu in the series of lanthanides. The nearly fivefold lower Tc, as against the expected value, is attributed to the divalent properties of Eu ions when in the compound investigated along with the weakly magnetic Eu3+ ions may be present and the strongly magnetic Eu2+ ones that is a strong destructive factor for superconductivity. Most of the spectra measured showed features that corresponds to two energy gaps whose values varied from contact to contact within 2Δs/kTc=2.2{\pm}4.7 and 2Δ1/kTc=5.1{\pm}11.7 for small and large gap, respectively. The corresponding variations for single-gap spectra are 2Δ/kTc = 2.6{\pm}6.4. The relatively large size of crystallites (no less than ~25 μ{m}) and the large number of contacts measured (several tens) suggest with a high degree of probability that the spectra obtained account quite fully for the gap distribution practically in all crystallographic directions. The data obtained and the absence of zero gaps in the measured spectra evidence in favor of the anisotropic s- or s\pm-symmetry of the order parameter in EuAsFeO0.85F0.15 that was revealed in other similar compounds with higher Tc. Thus, the character of the gap function Δ(k) in this compound is inconsistent with the d-wave superconductivity observed in some low-Tc pnictides.

cond-mat.supr-con↗

arXiv2009

Superconducting and magnetic properties of a new EuAsFeO0.85F0.15 superconductor

Polycrystalline samples of a new superconducting EuAsFeO0.85F0.15 compound with critical temperature Tc=11K were prepared by solid state synthesis. Its electric and magnetic properties have been investigated in magnetic fields from 0.1 to 140000 Oe. Critical magnetic fields Hc1, and Hc2 were measured and hence the magnetic penetration depths and the coherence length have been estimated. The temperature dependence Hc2 (T) exhibits clear hyperbolic - type behavior starting with the lowest fields. The data derived were used to estimate probable high Tc and Hc2 in compounds doped with rare-earths having small atomic radii.

cond-mat.supr-con↗

arXiv2006

Low temperature heat capacity of fullerite C60 doped with nitrogen

The heat capacity Cm of polycrystalline fullerite C60 doped with nitrogen has been measured in the temperature interval 2 - 13 K. The contributions to heat capacity from translational lattice vibrations (Debye contribution), orientational vibrations of the C60 molecules (Einstein contribution) and from the motion of the N2 molecules in the octahedral cavities of the C60 lattice have been estimated. However, we could not find (beyond the experimental error limits) any indications of the first - order phase transformation that had been detected earlier in the dilatometric investigation of the orientational N2-C60 glass. A possible explanation of this fact is proposed.

cond-mat.mtrl-sci↗