arXiv subjects

E. F. Talantsev

Publications and source records attributed to E. F. Talantsev.

At least 37 records · Page 2Linked to original sources

arXiv2022

The compliance of the upper critical field in magic-angle multilayer graphene with the Pauli limit

The Pauli limiting field represents fundamental magnetic field at which superconducting state collapses due to the spin-paramagnetic Cooper pair-breaking effect. Cao et al [1] reported that the upper critical field (i.e., the magnetic field at which the superconducting state collapses in experiment) in magic-angle twisted trilayer graphene (MATNG, N=3) in 2-3 times exceeds the Pauli limiting field in this material. This observation was interpreted as a violation of the Pauli-limiting field in MAT3G. Similar conclusions were recently reported by the same research group in MATNG (N=4,5) superlattices [2]. Here we point out that Cao et al [1] calculated the Pauli limiting field by the use of reduce (to the weak-coupling limit) full equation of the electron-phonon mediated superconductivity. Considering, that in the same paper, Cao et al [1] reported that MATNGs are strong coupled superconductors, we calculate the Pauli limiting field for strong coupled case and show that the observed upper critical fields in MATNGs comply with the Pauli limit. This implies that there is no violation of the Pauli limiting field in the Moire multilayer graphene superlattices.

cond-mat.mes-hall↗

arXiv2022

Trapped magnetic flux in hydrogen-rich high-temperature superconductors

Recent discoveries of superconductivity in hydrogen-rich compounds stabilized by high pressures have shown that a critical temperature of superconductivity Tc can reach near room temperature values. The current studies focus on the search for new superconductors with higher Tcs to understand the ultimate limit of conventional superconductivity, and high-Tc superconductors at lower pressures. However, high pressure conditions put serious limitations on experimental studies. Electrical transport measurements have long been the primary experimental technique for reliable detection of superconductivity at high pressures, whereas magnetic susceptibility measurements continue to be a challenge. Here, we dramatically changed the protocol of magnetic measurements to probe the trapped magnetic flux. We tested this technique on samples of H3S and LaH10 and propose it for a routine examination of superconductivity at high pressures. Using the temperature- and magnetic field dependences of the trapped flux we estimated Tc ~195 K, a lower critical field ~0.36 T, an irreversibility field ~1.7 T, a full penetration field ~8.8 T, the London penetration depth ~37 nm, and critical current densities jc(T) in H3S at ~155 GPa in a wide temperature range. The trapped flux method is found to be sensitive to a particular phase in a mixture of superconducting phases: concomitant phases of sulfur and hydrogen-depleted LaHx were detected. In contrast to the Meissner state occurring at low external magnetic fields, a magnetic response from the trapped flux at zero applied magnetic field is in tens times stronger and is not contaminated by the magnetic background of a bulky diamond anvil cell. This technique can be a powerful tool for the screening of new superconducting materials, the study of multiphase, contaminated samples, or samples with a low superconducting fraction at ambient pressure too.

cond-mat.supr-con↗

arXiv2022

Thermodynamic parameters of atomically thin superconductors derived from the upper critical field

The amplitude of ground state superconducting energy gap $Δ(0)$ and relative jump in electronic specific heat at the transition temperature, $Δ$$C$${/}$$γ$$T_c$, are primary fundamental parameters of any superconductor. There are several well-established techniques to measure these values for bulk samples. However, there is limited number of techniques which can be applied to measure these parameters in atomically thin superconductors. Here we proposed a new approach to extract $Δ(0)$ and $Δ$$C$${/}$$γ$$T_c$ in atomically thin superconductors by utilizing perpendicular, Bc2,perp(T) (when magnetic field is applied in perpendicular direction to the film surface), and parallel, Bc2,||(T) (when magnetic field is applied in parallel direction to the film surface), upper critical field data. Deduced parameters for few layers thick Al, Sn, NbSe2, MoS2, magic angle twisted trilayer graphene (MATTG), and WTe2 are well matched values expected for strong- and moderately strong-coupled electron-phonon mediated superconductors. Observed, in many atomically thin superconductors, an enhancement of Bc2,||(0) above the Pauli-Clogston-Chandrasekhar limiting field (i.e., magnetic field required to break the Cooper pair) is explained based on the sample geometry, without an assumption that some exotic pairing mechanism, for instance, Ising-type, is emergent in these materials.

cond-mat.supr-con↗

arXiv2022

Method to extracting the penetration field in superconductors from DC magnetization data

The lower critical field, Bc1, is one of the fundamental quantities of a superconductor which directly manifests the Cooper pair bulk density in the material. Despite this field can be measured by several techniques, the most conventional way is to calculate this field from experimentally measured DC penetration field, Bp, which is defined as the starting point of the deviation of the DC magnetization curve, M(Bappl), from a linear dependence. Surprisingly enough we found that there is no mathematical routine which describes how this starting point of deviation can be found. Here we proposed to extract Bp data from the fit of M(Bappl) dataset to the power law, where the threshold criterion Mc can be established by a convention. The advantage of this approach is that the procedure extracts one additional characteristic parameter, which is the power-law exponent. We demonstrated the applicability of the approach for polycrystalline ThIr3, WB4.2, BaTi2Bi2O, Th4H15, for Pb thin films and for Nb single crystal. Due to in majority of reports Bc1(T) analysis is limited by the extracting of the London penetration depth, here we advanced the analysis to extract primary thermodynamic superconducting parameters (i.e., the ground state superconducting energy gap, $Δ(0)$, the relative jump in electronic specific heat at transition temperature, $ΔC/C$, and the gap-to-transition temperature ratio, $2Δ(0)/(k_B T_c )$ from Bc1(T) data. This extraction was shown for Nb, ThIr3, TaRh2B2 and NbRh2B2.

cond-mat.supr-con↗

arXiv2022

Electron-phonon coupling constant and BCS ratios in (La,Nd)-H superhydride

Stoichiometric near room-temperature superconductors (i.e., $H_3S$ and $LaH_{10}$) exhibit so high ground state upper critical field, $B_{c2}(0)>100 T$, that the magnetic phase diagram in these materials cannot be measured in non-destructive experiments. However, recently, Semenok et al (arXiv2203.06500) proposed the idea to explore full magnetic phase diagram in NRTS samples in which the superconducting order parameter is suppressed by the magnetic element doping. If the element is uniformly distributed in the material, then the theory of the electron-phonon mediated superconductivity predicts the suppression of the order parameter in three-dimensional s-wave superconductor. Semenok et al (arXiv2203.06500) experimentally proved this idea by substituting La with the magnetic rare earth Nd in the $La_{1-x}Nd_{x}H_{10-y}$. As a result, $T_c$ in the $La_{1-x}Nd_{x}H_{10-y}$ (x=0.09) decreases to Tc~120 K, and the upper critical field decreases to $B_{c2}(T=41 K)=55 T$. While the exact hydrogen content should be further established in the $La_{1-x}Nd_{x}H_{10-y}$ (because similar $T_c$ suppression was observed in hydrogen deficient $LaH_{10-y}$ reported by Drozdov et al (2019 Nature 569 528)), a significant part of the full magnetic phase diagram for $La_{1-x}Nd_{x}H_{10-y}$ (x=0.09) was measured. Here we analyzed reported Semenok et al (arXiv2203.06500) data for $La_{1-x}Nd_{x}H_{10-y}$ (x=0.09) compressed at P=180 GPa and deduced: (a) Debye temperature, $T_θ=1156 K$; (b) the electron-phonon coupling constant, $λ_{e-ph}=1.65$; (c) the ground state superconducting energy gap, $Δ(0)=20.2 meV$; (d) the gap-to-transition temperature ratio, $2Δ(0)/k_BT_c=4.0$; and (e) the relative jump in specific heat at $T_c$, $ΔC/C=1.68$. The deduced values indicate that $La_{1-x}Nd_{x}H_{10-y}$ (x=0.09; P=180 GPa) is moderately strong coupled s-wave superconductor.

cond-mat.supr-con↗

arXiv2022

Universal Fermi velocity in highly compressed hydride superconductors

Fermi velocity, $v_F$, is one of the primary characteristics of any conductor, including superconductors. For conductors at ambient pressure several experimental techniques have been developed to measure $v_F$ and, for instance, Zhou et al (Nature 423 398 (2003)) reported that high-Tc cuprates exhibit universal nodal Fermi velocity of $v_F$ = $2.7*10^5$ m/s. However, there were no experimental techniques applied to measure $v_F$ in highly-compressed near-room-temperature superconductors (NRTS), due to experimental challenges. Here to answer a question about the existence of the universal Fermi velocity in NRTS materials, we analyzed full inventory of the ground-state upper critical field data, Bc2(0), for these materials and found that this class of superconductors exhibits universal Fermi velocity of $v_F$ = (1/1.3)*(2$Δ$(0)/(kBTc))*10^5 m/s (where $Δ(0)$ is ground state amplitude of the energy gap). Due to the ratio of 2$Δ$(0)/$({k_B}{T_c})$ is varying within a narrow arrange of 3.2 < 2$Δ$(0)/$({k_B}{T_c})$ < 5, then $v_F$ in NRTS materials is within the same ballpark with its high-Tc cuprates counterpart.

cond-mat.supr-con↗

arXiv2022

New scaling laws for pinning force density in superconductors

Since the report by Fietz and Webb (1968 Phys. Rev. 178 657), who considered the pinning force density, $|F_p| = |J_c \times B|$ (where $J_c$ is the critical current density and $B$ is applied magnetic field), in isotropic superconductors as a unique function of the reduced applied field, $B/B_{c2}$ (where $B_c2$ is the upper critical field), $|F_p|$ has been scaled based on B/B_c2 ratio, for which there is widely used scaling law of $|F_p(B)|=F_{p,max}((B/B_{c2})^p)((1-B/B_{c2})^q)$, where $F_{p,max}$, $B_{c2}$, $p$, and $q$ are free-fitting parameters, proposed by Kramer (1973 J. Appl. Phys. 44 1360) and Dew-Hughes (1974 Phil. Mag. 30 293). To describe $|F_p(B)|$ in high-temperature superconductors, Kramer-Dew-Hughes scaling law was modified by (a) an assumption of the angular dependence of all free-fitting parameters on the rotation angle and (b) by the replacement of the upper critical field, $B_{c2}$, by the irreversibility field, $B_{irr}$. Here we note that the pinning force density is also a function of critical current density and, thus, $|F_p(J_c)|$ scaling law should exist. In an attempt to reveal this law, we considered the full $|F_p(B,J_c)|$ function and reported that there are three distinctive characteristic ranges of $(B/B_{c2}, J_c/(J_c(sf)))$ (where $J_c(sf)$ is the self-field critical current density) on which $|F_p(B,J_c)|$ can be splatted. Several new scaling laws for $|F_p(J_c)|$ were proposed, discussed, and applied to scale $|F_p(J_c)|$ in MgB2, NdFeAs(O,F), REBCO, and near-room temperature superconducting super hydrides (La,Y)H10 and YH6. We pointed out that the general scaling law for the pinning force density is on the quest.

cond-mat.supr-con↗

arXiv2021

The electron-phonon coupling constant and the Debye temperature in polyhydrides of thorium, hexadeuteride of yttrium, and metallic hydrogen phase III

Milestone experimental discovery of superconductivity above 200 K in highly-compressed sulphur hydride by Drozdov (Nature 525, 73 (2015)) sparked experimental and theoretical investigations of metallic hydrides. Since then, a dozen of superconducting binary and ternary polyhydrides have been discovered. For instance, there are three superconducting polyhydrides of thorium: Th4H15, ThH9, and ThH10 and four polyhydrides of yttrium: YH4, YH6, YH7, YH9. In addition to binary and ternary hydrogen-based metallic compounds, recently Eremets (arXiv:2109.11104) reported on the metallization of hydrogen, which exhibits a phase transition into metallic hydrogen phase III at P>330 GPa and T<200 K. Here we analyzed temperature-dependent resistance, R(T), in polyhydrides of thorium, hexadeuteride of yttrium and in hydrogen phase III and deduced the Debye temperature, $T$$_θ$, and the electron-phonon coupling constant, $λ_{e-ph}$, for these conductors. We found that Th4H15 phase exhibits $λ_{e-ph}$ = 0.82-0.99 which is in a very good agreement with experimental value of $λ_{e-ph}$ = 0.84 deduced from heat capacity measurements (Miller, Phys. Rev. B 14, 2795 (1976)). For P63/mmc-ThH9 phase (P = 170 GPa) we deduced $λ_{e-ph}$(170 GPa) = 1.46, which is in a reasonable agreement with $λ_{e-ph}$ reported by Semenok (Materials Today 33, 36 (2020)). Deduced $λ_{e-ph}$(170 GPa) = 1.70 for Fm-3m-ThH10 is in remarkable agreement with first-principles calculated $λ_{e-ph}$(174 GPa)=1.75 (Semenok, Materials Today 33, 36 (2020)). Deduced $λ_{e-ph}$(172 GPa) = 1.90 for Im-3m-YD6 is also in excellent agreement with first-principles calculated $λ_{e-ph}$(165 GPa)=1.80 (Troyan, Advanced Materials 33, 2006832 (2021)). And finally, we deduced $T$$_θ$(402 GPa) = 727 K for hydrogen phase III which implies that $λ_{e-ph}$(402 GPa)<1.7 in this metal.

cond-mat.supr-con↗

arXiv2021

The dominance of non-electron-phonon charge carrier interaction in highly-compressed superhydrides

The primary mechanism governing the emergence of near-room-temperature superconductivity in superhydrides is widely accepted to be the electron-phonon interaction. If so, the temperature dependent resistance, R(T), in these materials should obey the Bloch-Grüneisen equation, where the power-law exponent, p, should be equal to the exact integer value of p=5. On the other hand, there is a well-established theoretical result that pure electron-magnon interaction should be manifested by p=3, and p=2 is the value for pure electron-electron interaction. Here we aimed to reveal the type of charge carrier interaction in the layered transition metal dichalcogenides PdTe2, high-entropy alloy (ScZrNb)0.65[RhPd]0.35, and highly-compressed elemental boron and superhydrides H3S, LaHx, PrH9 and BaH12 by fitting the temperature dependent resistance of these materials to the Bloch-Grüneisen equation where the power-law exponent, p, is a free-fitting parameter. In the result, we showed that the high-entropy alloy (ScZrNb)0.65[RhPd]0.35 exhibited pure electron-phonon mediated superconductivity with p = 4.9. Unexpectedly we revealed that all studied superhydrides exhibit 1.8 < p < 3.2. This implies that it is unlikely that the electron-phonon interaction is the primary mechanism for the Cooper pairs formation in highly-compressed superhydrides and alternative pairing mechanisms, for instance, the electron-magnon, the electron-polaron, the electron-electron or other, should be considered as the origin for the emergence of near-room-temperature superconductivity in these compounds.

cond-mat.supr-con↗

arXiv2021

Classifying charge carrier interaction in highly-compressed elements and silane

Since pivotal experimental discovery of the near-room-temperature superconductivity (NRTS) in highly-compressed sulphur hydride by Drozdov et al (2015 Nature 525 73-76), more than a dozen of binary and of ternary hydrogen-rich phases exhibited superconducting transition above 100 K have been discovered to date. There is a widely accepted theoretical point of view that primary mechanism governing the emergence of superconductivity in hydrogen-rich phases is the electron-phonon pairing. However, our recent analysis of experimental temperature dependent resistance in $H_{3}S$, $LaH_{x}$, $PrH_{9}$ and $BaH_{12}$ (arXiv: 2104.14145) showed that these compounds exhibit the dominance of non-electron-phonon charge carrier interaction and, thus, it is unlikely that the electron-phonon pairing is the primary mechanism for the emergence of superconductivity in these materials. Here we use the same approach to reveal charge carrier interaction in highly-compressed lithium, black phosphorous, sulfur, and silane. We found that all these superconductors exhibit the dominance of non-electron-phonon charge carrier interaction. This explains the failure of high-Tc values predicted for these materials by the first-principles calculations which utilized the electron-phonon pairing as the mechanism for the emergence of superconductivity in these materials. Our result implies that alternative pairing mechanisms (i.e., electron-magnon, electron-polaron, electron-electron, etc.) should be tested within first-principles calculations approach as possible mechanisms for the emergence of superconductivity in highly-compressed superconductors.

cond-mat.supr-con↗

arXiv2021

Comparison of highly-compressed C2/m-SnH12 superhydride with conventional superconductors

Satterthwaite and Toepke (1970 Phys. Rev. Lett. 25 741) predicted high-temperature superconductivity in hydrogen-rich metallic alloys, based on an idea that these compounds should exhibit high Debye frequency of the proton lattice, which boosts the superconducting transition temperature, Tc. The idea has got full confirmation more than four decades later when Drozdov et al (2015 Nature 525 73) experimentally discovered near-room-temperature superconductivity in highly-compressed sulphur superhydride, H3S. To date, more than a dozen of high-temperature hydrogen-rich superconducting phases in Ba-H, Pr-H, P-H, Pt-H, Ce-H, Th-H, S-H, Y-H, La-H, and (La,Y)-H systems have been synthesized and, recently, Hong et al (2021 arXiv:2101.02846) reported on the discovery of C2/m-SnH12 phase with superconducting transition temperature of Tc ~ 70 K. Here we analyse the magnetoresistance data, R(T,B), of C2/m-SnH12 phase and report that this superhydride exhibits the ground state superconducting gap of $Δ$(0) = 9.2 meV, the ratio of 2$Δ$(0)/k$_B$Tc = 3.3, and 0.010 < Tc/Tf < 0.014 (where Tf is the Fermi temperature) and, thus, C2/m-SnH12 falls into unconventional superconductors band in the Uemura plot.

cond-mat.supr-con↗

arXiv2021

Quantifying the charge carrier interaction in metallic twisted graphene superlattices

The mechanism of charge carrier interaction in twisted bilayer graphene (TBG) remains an unresolved problem, where some researchers proposed the dominance of the electron-phonon interaction, while the others showed evidence for electron-electron or electron-magnon interactions. Here we propose to resolve this problem by generalizing the Bloch-Grüneisen equation and using it for the analysis of the temperature dependent resistivity in TBG. It is a well-established theoretical result that the Bloch-Grüneisen equation power-law exponent, n, exhibits exact integer values for certain mechanisms. For instance, n=5 implies the electron-phonon interaction, n=3 is associated with electron-magnon interaction and n=2 applies to the electron-electron interaction. Here we interpret the linear temperature-dependent resistance, widely observed in TBG, as n$\rightarrow$1, which implies the quasielastic charge interaction with acoustic phonons. Thus, we fitted TBG resistance curves to the Bloch-Grüneisen equation, where we propose that n is a free-fitting parameter. We found that TBGs have a smoothly varied n-value (ranging from 1.4 to 4.4) depending on the Moiré superlattice constant, $λ$, or the charge carrier concentration. This implies that different mechanisms smoothly transition from one to another. The proposed generalized Bloch-Grüneisen equation is applicable to a wide range of problems, including the Earth geology.

cond-mat.mes-hall↗

arXiv2020

The electron-phonon coupling constant, the Fermi temperature and unconventional superconductivity in the carbonaceous sulfur hydride 190 K superconductor

Recently, Snider et al (2020 Nature 586 373) reported on the observation of superconductivity in highly-compressed carbonaceous sulfur hydride, $H_x$$(S,C)_y$. The highest critical temperature in $H_x$$(S,C)_y$ by 5 K exceeds previous record of Tc = 280 K reported by Somayazulu et al (2019 Phys. Rev. Lett. 122 027001) for highly-compressed $La$$H_{10}$. In this paper we analyze experimental temperature dependent magnetoresistance data, R(T,B), reported by Snider et al. The analysis shows that $H_x$$(S,C)_y$ compound exhibited Tc = 190 K (P = 210 GPa) has the electron-phonon coupling constant $λ$$_{e-ph}$ = 2.0 and the ratio of critical temperature, Tc, to the Fermi temperature, Tf, in the range of 0.011 < Tc/Tf < 0.018. These deduced values are very close to ones reported for $H_x$$S$ at P = 155-165 GPa by Drozdov et al (2015 Nature 525 73). This means that in all considered scenarios the carbonaceous sulfur hydride 190 K superconductor falls into unconventional superconductors band in the Uemura plot, where all other highly-compressed super-hydride/deuterides are located. It should be noted that that our analysis shows that all raw R(T,B) datasets for $H_x$$(S,C)_y$ samples for which Snider et al (2020 Nature 586 373) reported Tc > 200 K cannot be characterized as reliable data sources. Thus, independent experimental confirmation/disprove high-Tc values in the carbonaceous sulfur hydride is required.

cond-mat.supr-con↗

arXiv2020

Cooper pair ring model

The superconducting state starts to collapse when the externally applied magnetic field exceeds the Meissner-Ochsenfeld critical field, Bc,MO, which in type-I superconductors is the thermodynamic critical field, while in type-II superconductors this field is the lower critical field. Here we show that both critical fields can be described by the universal equation of $B$$_{c,MO}$=$μ$$_0$$n$$μ$$_B$$ln(1+2$$^{0.5}$$κ$), where $μ$$_0$ is the magnetic permeability of free space, $n$ is the Cooper pairs density, and $μ$$_B$ is the Bohr magneton, and $κ$ is the Ginzburg-Landau parameter. As a result, the Meissner-Ochsenfeld field can be defined as the field at which each Cooper pair exhibits the diamagnetic moment of one Bohr magneton with a multiplicative pre-factor of $ln(1+2$$^{0.5}$$κ$). In the two-dimensional case this implies that the Cooper pair center of mass is spatially confined within a ring with inner radius $ξ$ and outer radius of $ξ$+2$^{0.5}$$λ$, where $ξ$ is the coherence length and $λ$ is the London penetration depth. This means that the superconducting transition is associated not only with the charge carrier pairing, but that the pairs exhibit a new topological state with genus 1.

cond-mat.supr-con↗

arXiv2020

In-plane p-wave coherence length in iron-based superconductors

High-temperature superconductivity in iron-based layered compounds discovered by Hosono group (Kamihara et al 2006 J. Am. Chem. Soc. 128 10012) is fascinating physical phenomenon which still has many unanswered questions. One of these questions is the superconducting gap symmetry in iron-based superconductors (IBS), for which the most agreed concept is multiple-band $s$-wave symmetry. Recently, an alternative concept of single-band $p$-wave symmetry has been proposed. To disprove/reaffirm the latter concept, in this paper we analyse temperature dependent in-plane coherence length in FeSe, FeSe1-xTex, Ba(Fe1-x(Co,Ni)x)2As2 and Ca10(Pt4As8)((Fe,Pt)2As2)5 in order to extract the gap-to-critical-temperature ratio, 2$Δ$(0)/$k$$_B$$T$$_c$, and the specific-heat-jump ratio, $Δ$C/C,in these compounds. In the result, we report that deduced ratios are in a good agreement with the concept of single-band $p$-wave superconductivity in these materials.

cond-mat.supr-con↗

arXiv2020

Piecewise model with two overlapped stages for the structure formation and hardening upon severe plastic deformation

The evolution of metals micro/nano-structure upon severe plastic deformation (SPD) is still far to be theoretically explained, while experimental datasets are persistently growing. Major problem associated with understanding of SPD is a synergetic effect of several competing processes which alter material structure. In this paper we propose a model to reveal, as free-fitting parameters, strain breakpoints where predominantly one mechanism determines the micro/nano-structure in SPD materials from material hardness vs true strain experimental data. The model is applied to analyse SPD data for pure polycrystalline iron and two distinctive strain breakpoints have been revealed.

cond-mat.mtrl-sci↗

arXiv2020

Double-valued strong-coupling corrections to Bardeen-Cooper-Schrieffer ratios

Experimental discovery of near-room-temperature (NRT) superconductivity in highly-compressed H$_3$S, LaH$_1$$_0$ and YH$_6$ restores fundamental interest to electron-phonon pairing mechanism in superconductors. One of prerequisites of phonon-mediated NRT superconductivity in highly-compressed hydrides is strong electron-phonon interaction, which can be quantified by dimensionless ratios of Bardeen-Cooper-Schrieffer (BCS) theory vs $k{_B}T{_c}$/(${\hslash}$$ω{_l}{_n}$), where Tc is the critical temperature and $ω{_l}{_n}$ is the logarithmic phonon frequency (Mitrovic et al. 1984 Phys. Rev. B 29 184). However, all known strong-coupling correction functions for BCS ratios are applicable for $k{_B}T{_c}$/(${\hslash}$$ω{_l}{_n}$)<0.20, which is not high enough $k{_B}T{_c}$/(${\hslash}$$ω{_l}{_n}$) range for NRT superconductors, because the latter exhibit variable values of 0.13 < $k{_B}T{_c}$/(${\hslash}$$ω{_l}{_n}$) < 0.32. In this paper, we reanalyze full experimental dataset (including data for highly-compressed H3S) and find that strong-coupling correction functions for the gap-to-critical-temperature ratio and for the specific-heat-jump ratio are double-valued nearly-linear functions of $k{_B}T{_c}$/(${\hslash}$$ω{_l}{_n}$).

cond-mat.supr-con↗

arXiv2020

Cooper pair trajectories in superconducting slab at self-field conditions

Dissipative-free electric current flow is one of the most fascinating and practically important property of superconductors. Theoretical consideration of the charge carriers flow in infinitely long rectangular slab of superconductor in the absence of external magnetic field (so called, self-field) is based on an assumption that the charge carriers have rectilinear trajectories in the direction of the current flow whereas the current density and magnetic flux density are decaying towards superconducting slab with London penetration depth as characteristic length. Here, we calculate charge particle trajectories (as single electron/hole, as Cooper pair) at self-field conditions and find that charge carriers do not follow intuitive rectilinear trajectories along the slab surface, but instead ones have meander shape trajectories which cross the whole thickness of the slab. Moreover, if the particle velocity is below some value, the charge moves in opposite direction to nominal current flow. This disturbance of the canonical magnetic flux density distribution and backward movement of Cooper pairs can be entire mechanism for power dissipation in superconductors.

cond-mat.supr-con↗