arXiv subjects

Evgeny F. Talantsev

Publications and source records attributed to Evgeny F. Talantsev.

17 recordsLinked to original sources

arXiv2026

On the estimating the superconducting volume fraction from the internal magnetic susceptibility

Zhang et al.$^1$ reported zero-field cooled (ZFC) and field cooled (FC) data measured in a highly compressed $Pr_4Ni_3O_{10}$ single crystal. These measurements provide unambiguous confirmation of bulk superconductivity in pressurized Ruddlesden-Popper nickelates. Zhang et al.$^1$ applied an equation (described in Refs.$^{2,3}$) to recalculate ZFC data measured in a $Pr_4Ni_3O_{10}$ (sample S3) in volume fraction $f$ of the superconducting phase in the sample. In result$^1$, $f = 0.85$ was reported for sample S3 at pressure P = 40.2 GPa. The key postulate of the methodology for the calculation of $f$ (see also works$^{4-6}$) is that $f$ is equal to the amplitude of the internal magnetic susceptibility $\vert χ_{internal} \vert $, or $ f = \vert χ_{internal} \vert $. Here we argue that this postulate is incorrect and present counterexample where the $Pr_4Ni_3O_{10}$ sample S3 can exhibit $f < 0.10$ and $\vert χ_{internal} \vert = 0.82 $. In the result, we addressed recent Replies$^{2,3}$ on our Comments$^{7,8}$. Considering that the postulate $ f = \vert χ_{internal} \vert $ is widely used in superconductivity, we extend our request to reconsider the validity of this postulate in the entire field of superconductivity.

cond-mat.supr-con↗

arXiv2026

Nanocrystalline structure and strain in magnesium under extreme dynamic compression

The study of materials behavior under extreme conditions is fundamental to science and modern technology. Fast ramp compression is a unique method for exploring materials behavior and phase transformations under extreme conditions. One unexplored feature of this method is the nanoscale structure of the material under dynamic compression. This leaves a gap in understanding the details of phase transformations under fast ramp compression. Here, we made a first step in the exploration by applying the Williamson-Hall (WH) analysis to X-ray diffraction data (XRD) measured in magnesium subjected to fast ramp compression at four pressures. We found that at $P = 309 GPa$ magnesium in bcc-like phase has an average crystalline size $D = (2.2 \pm 0.7) nm$ and microstrain $\varepsilon = (-0.011 \pm 0.007)$. At $P = 409 GPa$, magnesium demonstrates $D = (4.5 \pm 3) nm$ with $\varepsilon = (-0.003 \pm 0.007)$. At $P = 563 GPa$, Fmmm magnesium has crystalline size $D = (2.6 \pm 0.5) nm$ with microstrain $\varepsilon = (-0.004 \pm 0.004)$. At $P = 959 GPa$, we revealed that sh-magnesium exhibits average size of $D > 12 nm$ and relatively high value of microstrain $\varepsilon = (0.011 \pm 0.002)$. In the result, we report the first microstructural evolution insights of magnesium under fast ramp compression.

cond-mat.mtrl-sci↗

arXiv2026

Threefold error in the reported zero-field cooled magnetic moment of single crystal $La_2SmNi_2O_7$

For a relatively long time, the observation of the DC diamagnetic state in highly compressed nickelate superconductors [1],[2] has been a challenging experimental problem. And recently Li et al.[3] reported on the measurements of the DC diamagnetism in zero-field-cooled (ZFC) and field-cooled (FC) pressurized single crystal $La_2SmNi_2O_7$. From the analysis of experimental data, Li et al.[3] reported that the superconducting phase fraction in their $La_2SmNi_2O_7$ sample measured in the ZFC mode is 62.1%, and the superconducting phase fraction in the FC mode is 14.4%. It should be clarified that we regard the measurements of the DC diamagnetic state [3] in $La_2SmNi_2O_7$ (and more recently in $Pr_4Ni_3O_{10}$ [4]) as outstanding experimental results confirming bulk superconductivity in pressurized nickelates. However, we should note that Li et al.[3] made a threefold error in their calculations of the superconducting phase fraction in $La_2SmNi_2O_7$. We believe that correcting this and other errors in Ref.[3] will benefit the physics community.

cond-mat.supr-con↗

arXiv2026

Nearly twofold overestimation of the superconducting volume fraction in pressurized Ruddlesden-Popper nickelates

The detection of the DC diamagnetic state in pressurized Ruddlesden-Popper nickelates remained an unsolved experimental problem until recent experiments in which Zhu et al.$^1$ measured the DC diamagnetic responses in zero-field cooled (ZFC) mode in pressurized La4Ni3O10. Zhu et al.$^1$ reported that the ratio of the measured ZFC magnetic moment to the Meissner magnetic moment of the sample (and this ratio was termed the superconducting volume fraction$f$) reaches 81-86%. We regard outstanding experimental results$^1$; however, our calculations based on the reported experimental datasets$^1$ using the standard procedure showed the ratio to be 51-59%. Upon our request, Zhu et al.$^1$ provided detailed explanations and the equation they used to calculate$f$. To our knowledge, the procedure$^1$ and equation$^1$ for calculating $f$ have never been mentioned or described before, including in Ref.$^1$. Here we argue that the proposed equation$^1$ and procedure$^1$ are incorrect, and that this equation$^1$ results in multiple overestimations of the superconducting volume fraction in the sample. This overestimation error affects all superconducting volume fractions $f$ in Ruddlesden-Popper nickelates reported to date$^{1-4}$. Therefore, we describe the error we discovered in this paper.

cond-mat.supr-con↗

arXiv2026

Best practices for a proper evaluation and conversion of physical property equations in superconductors: the examples of WHH formulation, Bean model and other cases of interest

In recent years there have been growing concerns about the proper evaluation of physical properties of superconductors, in particular for quantities extracted from magnetic characterizations. Errors can and often do occur due to the following issues: i) several measurement instruments still use Gaussian & cgs-emu units instead of the preferable International System (SI) units; ii) there are decades of valuable publications where, however, equations were expressed in Gaussian & cgs-emu or other unit systems or where constants were normalized to unity, which requires proper understanding and unit conversion in order to correctly evaluate the measured physical quantities; iii) the conversion between unit systems sometimes appears challenging and may not be properly performed. In this paper we will describe how to properly convert physical quantities relevant for the evaluation of magnetic and other properties focusing on the still most used unit systems, SI and Gaussian & cgs-emu. We will provide examples of how to properly verify and understand the physical formulae. We will include examples for the correct method to determine the critical current density Jc of a superconductor from the measurement of its magnetic hysteresis loop through the Bean model, and the correct conversion to SI of the equations for Hc2(T) according to the Werthamer-Helfand-Hohenberg (WHH) formulation. The goals of this paper are to make the readers aware of the unit conversion issue, to provide useful hands-on tools for proper conversion and to strongly encourage future exclusive use of the SI units and formulae.

cond-mat.supr-con↗

arXiv2025

Long-Term Stability of Superconducting Metal Superhydrides

Zhou et al., in their recent publication (Nat. Commun. 16, 1135, 2025), reported the synthesis of lanthanum superhydride, LaHx (x = 10.2-11.1), by laser heating LaH3 with NH3BH3 at a pressure of 170 GPa and investigated the temporal evolution of the NMR spectra of the reaction products. They observed a gradual decrease in the 1H-NMR signal intensity assigned to the synthesized metal hydride, accompanied by an increase in molecular hydrogen within the sample chamber over a period of 50 days. Based on these observations, the authors concluded that LaH10 progressively decomposes into LaH3 and H2 within two months after synthesis at its formation pressure of 170 GPa. Here, we demonstrate that, under their formation conditions, metal superhydrides are thermodynamically more stable than metal trihydrides. Furthermore, we present direct experimental evidence - based on X-ray diffraction and four-probe electrical resistance measurements - confirming the stability of both the crystal lattice and high-temperature superconducting properties of the Fm-3m-LaH10 phase for more than five years. This long-term stability is consistent with predictions from quantum chemistry calculations.

cond-mat.supr-con↗

arXiv2025

Structural and superconducting parameters of highly compressed sulfur

Sulfur was the first nonmetal element which was transformed to a superconductor by applying megabar pressure. Recent pioneering experimental developments in measuring the superconducting energy gap $Δ(T)$ in compressed sulfur using tunneling spectroscopy (Du $\textit{et al}$., $\textit{Phys. Rev. Lett.}$ $\textbf{133}$, 036002 (2024)) initiated an interest in better understanding real atomic structure and superconducting properties of this element at high pressure. Here, we analyzed available experimental data on highly compressed sulfur, and, from the $Δ(T)$ data reported by Du $\textit{et al}$. (2024), we extracted the specific heat jump at the transition temperature of $ΔC_{el}/γT_{c} = 1.8$. We also developed a model to extract the Debye temperatures $Θ_D$ for sulfur and $H_{3}S$ in two-phases sample from the temperature-dependent resistance $R(T)$. for better understanding of material structure, here we proposed to use a size-strain map for highly compressed samples, and we revealed this size-strain map for laser-heated sulfur in a diamond anvil cell with a mixture of sulfur and $H{_3}S$. Finally, we found that superconducting sulfur exhibits a moderate level of nonadiabaticity $0.04 \leq Θ_{D}/T_{F} \leq 0.15$ (where $T_{F}$ is the Fermi temperature), which is similar to $MgB_2$, pnictides, cuprates, $La_{4}H_{23}$, $ThH_{9}$, $H_{3}S$, $LaBeH_{8}$, and $LaH_{10}$.

cond-mat.supr-con↗

arXiv2024

Fundamental nature of the self-field critical current in superconductors

The ability to conduct electric current without dissipating energy is a property of superconductors that is used in magnetic systems utilized in healthcare, natural sciences, and ongoing global projects in nuclear fusion and aviation. The highest dissipation-less current is named the critical current, and this is one of the prime practical properties of superconductors (together with the critical current density, Jc). Recently, Goyal et al reported a record high Jc~190 MA/cm2 at 4.2 K in (RE)BCO films, exceeding the highest Jc in the best commercial (RE)BCO wires by a factor of five. Based on the huge potential practical impact of this high Jc, we examined the raw experimental data and found that this high value originates from an error in the conversion of units. The real Jc is 10 times smaller than the reported Jc, consistent with values currently achieved by many manufacturers.

cond-mat.supr-con↗

arXiv2022

A disorder-sensitive emergent vortex phase identified in high-Tc superconductor (Li,Fe)OHFeSe

The magneto-transport properties are systematically measured under c-direction fields up to 33 T for a series of single-crystal films of intercalated iron-selenide superconductor (Li,Fe)OHFeSe. The film samples with varying degree of disorder are grown hydrothermally. We observe a magnetic-field-enhanced shoulder-like feature in the mixed state of the high-Tc (Li,Fe)OHFeSe films with weak disorder, while the feature fades away in the films with enhanced disorder. The irreversibility field is significantly suppressed to lower temperatures with the appearance of the shoulder feature. Based on the experiment and model analysis, we establish a new vortex phase diagram for the weakly disordered high-Tc (Li,Fe)OHFeSe, which features an emergent dissipative vortex phase intermediate between the common vortex glass and liquid phases. The reason for the emergence of this intermediate vortex state is further discussed based on related experiments and models.

cond-mat.supr-con↗

arXiv2021

Resistive transition of hydrogen-rich superconductors

Critical temperature, $T_c$, and the transition width, $Δ$$T_c$, are two primary parameters of the superconducting transition. The latter parameter reflects the superconducting state disturbance originating from the thermodynamic fluctuations, atomic disorder, applied magnetic field, the presence of secondary crystalline phases, applied pressure, etc. Recently, Hirsch and Marsiglio (2020 arXiv:2012.12796) performed an analysis of the transition width in several near-room-temperature superconductors (NRTS) and reported that the reduced transition width, $Δ$$T_c$$/$$T_c$, in these materials does not follow a conventional trend of transition width broadening on applied magnetic field observed in low- and high-$T_c$ superconductors. Here we present thorough mathematical analysis of the magnetoresistive data, $\it{R(T,B)}$, for the high-entropy alloy $(ScZrNb)_{0.65}$$[RhPd]_{0.35}$ and hydrogen-rich superconductors of Im-3m-$H_{3}S$, C2/m-$LaH_{10}$ and P63/mmc-$CeH_9$. We found that the reduced transition width, $Δ$$T_c$$/$$T_c$, in these materials does follow a conventional broadening trend on applied magnetic field.

cond-mat.supr-con↗

arXiv2020

Superconductivity emerging from a stripe charge order in IrTe2 nanoflakes

Superconductivity in the vicinity of a competing electronic order often manifests itself with a superconducting dome, centred at a presumed quantum critical point in the phase diagram. This common feature, found in many unconventional superconductors, has supported a prevalent scenario that fluctuations or partial melting of a parent order are essential for inducing or enhancing superconductivity. Here we present a contrary example, found in IrTe2 nanoflakes of which the superconducting dome is identified well inside the parent stripe charge ordering phase in the thickness-dependent phase diagram. The coexisting stripe charge order in IrTe2 nanoflakes significantly increases the out-of-plane coherence length and the coupling strength of superconductivity, in contrast to the doped bulk IrTe2. These findings clarify that the inherent instabilities of the parent stripe phaseare sufficient to induce superconductivity in IrTe2 without its complete or partial melting. Our study highlights the thickness control as an effective means to unveil intrinsic phase diagrams of correlated vdW materials.

cond-mat.supr-con↗

arXiv2018

Universal scaling of the self-field critical current in superconductors: from sub-nanometre to millimetre size

Universal scaling behaviour in superconductors has significantly elucidated fluctuation and phase transition phenomena in these materials. However, universal behaviour for the most practical property, the critical current, was not contemplated because prevailing models invoke nucleation and migration of flux vortices. Such migration depends critically on pinning, and the detailed microstructure naturally differs from one material to another, even within a single material. Through microstructural engineering there have been ongoing improvements in the field-dependent critical current, thus illustrating its nonuniversal behaviour. But here we demonstrate the universal size scaling of the self-field critical current for any superconductor, of any symmetry, geometry or band multiplicity. Key to our analysis is the huge range of sample dimensions, from single-atomic-layer to mm-scale. These have widely variable microstructure with transition temperatures ranging from 1.2 K to the current record, 203 K. In all cases the critical current is governed by a fundamental surface current density limit given by the relevant critical field divided by the penetration depth.

cond-mat.supr-con↗

arXiv2018

Current distribution across type II superconducting films: a new vortex-free critical state

The current distribution across the thickness of a current-carrying rectangular film in the Meissner state was established long ago by the London brothers. The distribution across the width is more complicated but was later shown to be highly non-uniform, diverging at the edges. Accordingly, the standard view for type II superconductors is that vortices enter at the edges and, with increasing current, are driven inwards until they self-annihilate at the centre, causing dissipation. This condition is presumed to define the critical current. However we have shown that, under self-field (no external field), the transport critical current is a London surface current where the surface current density equals the critical field divided by λ, across the entire width. The critical current distribution must therefore be uniform. Here we report studies of the current and field distribution across commercial YBa2Cu3O7 conductors and confirm the accepted non-uniform distribution at low current but demonstrate a radical crossover to a uniform distribution at critical current. This crossover ends discontinuously at a singularity and calculations quantitatively confirm these results in detail. The onset of self-field dissipation is, unexpectedly, thermodynamic in character and the implied vortex-free critical state seems to require new physics.

cond-mat.supr-con↗

arXiv2018

The onset of dissipation in high-temperature superconductors: magnetic hysteresis and field dependence

Recently, we showed that the self-field transport critical current, Ic(sf), of a superconducting wire can be defined in a more fundamental way than the conventional (and arbitrary) electric field criterion, Ec = 1 microV/cm. We defined Ic(sf) as the threshold current, Ic,B, at which the perpendicular component of the local magnetic flux density, measured at any point on the surface of a high-temperature superconducting tape, abruptly crosses over from a non-linear to a linear dependence with increasing transport current. This effect results from the current distribution across the tape width progressively transitioning from non-uniform to uniform. The completion of this progressive transition was found to be singular. It coincides with the first discernible onset of dissipation and immediately precedes the formation of a measureable electric field. Here, we show that the same Ic,B definition of critical currents applies in the presence of an external applied magnetic field. In all experimental data presented here Ic,B is found to be significantly (10-30%) lower than Ic,E determined by the common electric field criterion of Ec = 1 microV/cm, and Ec to be up to 50 times lower at Ic,B than at Ic,E.

cond-mat.supr-con↗

arXiv2017

Thermodynamic parameters of single- or multi-band superconductors derived from self-field critical currents

Key questions for any superconductor include: what is its maximum dissipation-free electrical current (its `critical current') and can this be used to extract fundamental thermodynamic parameters? Present models focus on depinning of magnetic vortices and implicate materials engineering to maximise pinning performance. But recently we showed that the self-field critical current for thin films is a universal property, independent of microstructure, controlled only by the penetration depth. Here we generalise this observation to include thin films, wires or nanowires of single- or multi-band s-wave and d-wave superconductors. Using extended BCS theory we consider dissipation-free self-field transport currents as Meissner-London currents, avoiding the concept of pinning altogether. We find quite generally, for type I or type II superconductors, the current is limited by the relevant critical field divided by the penetration depth. Our fits to 62 available data sets, from zinc nanowires to compressed sulphur hydride with critical temperatures of 0.65 to 203 K, respectively, are excellent. Extracted London penetration depths, superconducting energy gaps and specific heat jumps agree well with reported bulk values. For multiband or multiphase samples we accurately recover individual band contributions and phase fractions.

cond-mat.supr-con↗

arXiv2017

London penetration depth and thermal fluctuations in the sulphur hydride 203 K superconductor

Recently, compressed H$_2$S has been shown to become superconducting at 203 K under a pressure of 155 GPa. One might expect fluctuations to dominate at such temperatures. Using the magnetisation critical current, we determine the ground-state London penetration depth, $λ_0$=189 nm, and the superconducting energy gap, $Δ_0$=27.8 meV, and find these parameters are similar to those of cuprate superconductors. We also determine the fluctuation temperature scale, $T_{\textrm{fluc}}=1470$ K, which shows that, unlike the cuprates, $T_c$ of the hydride is not limited by fluctuations. This is due to its three dimensionality and suggests the search for better superconductors should refocus on three-dimensional systems where the inevitable thermal fluctuations are less likely to reduce the observed $T_c$.

cond-mat.supr-con↗

arXiv2016

Universal self-field critical current for thin-film superconductors

For any practical superconductor the magnitude of the critical current density, $J_\textrm{c}$, is crucially important. It sets the upper limit for current in the conductor. Usually $J_\textrm{c}$ falls rapidly with increasing external magnetic field but even in zero external field the current flowing in the conductor generates a self-field which limits $J_\textrm{c}$. Here we show for thin films of thickness less than the London penetration depth, $λ$, this limiting $J_\textrm{c}$ adopts a universal value for all superconductors - metals, oxides, cuprates, pnictides, borocarbides and heavy Fermions. For type I superconductors, it is $H_{\textrm{c}}/λ$ where $H_\textrm{c}$ is the thermodynamic critical field. But surprisingly for type II superconductors we find the self-field $J_\textrm{c}$ is $H_{\textrm{c}1}/λ$ where $H_{\textrm{c}1}$ is the lower critical field. $J_\textrm{c}$ is thus fundamentally determined and this provides a simple means to extract absolute values of $λ(T)$ and, from its temperature dependence, the symmetry and magnitude of the superconducting gap.

cond-mat.supr-con↗