Superconducting Parameters Research Articles

Understanding vortex dynamics in CaK(Fe,Ni)4As4 and Ba(Fe,Co)2As2 single crystals under the influence of random point disorder

Abstract We report on the influence of doping on vortex dynamics in 3 MeV proton-irradiated single crystals of CaK(Fe1−x Ni x )4As4 (1144, x = 0.015, 0.025, and 0.03) and Ba(Fe1−x Co x )2As2 (x = 0.04, 0.062, 0.066 and 0.074). Non-irradiated crystals of the 1144 system display superconducting critical temperatures ranging from 31 K for x = 0.015–20.5 K, as doping increases to 0.03. On the other hand, pristine crystals of the 122 system show Tc values between 14.6 and 23.6 K, with the maximum Tc occurring at intermediate doping levels. The fluence was set at 3 × 1016 p cm−2, resulting in a decrease in the Tc by around 1.5 K for all samples and significantly affecting the vortex dynamics by reducing the flux creep relaxation compared to previously reported values for unirradiated crystals. Parameters such as vortex pinning energy U 0 and the glassy exponent μ dependencies on doping and magnetic field strength are identified. For the 1144 system, U 0 reaches values approaching 500 K for small fields in samples with Tc = 29.3 K (x = 0.015), systematically decreasing to around 200 K as Tc falls below 20 K. Furthermore, U 0 decreases as the field increases to 3 T for the same sample, varying from approximately 250 K to 100 K as Tc decreases. These changes are typically accompanied by modifications in μ, gradually increasing from values around 1 towards 1.5, corresponding to small bundle relaxation in the collective creep theory. Despite differences in the substitutional disorder and magnetic phase diagram with respect to the 1144 system, the results for 122 single crystals follow a similar tendency in which U 0 usually reduces and μ increase rise as the applied magnetic field is increased. Due to moderate U 0 in these systems (few hundreds of kelvins), the resulting decay of persistent current at liquid helium temperatures is primarily determined by a balance between U 0 and bundle size contribution. These findings provide valuable insights for potential applications of these systems, particularly in the context of intrinsic superconducting parameters and the resulting pinning landscape.

Superconductivity in TiZrNb and TiZrNbHf bulk equimolar alloys

We have prepared and investigated superconducting equimolar medium-entropy alloys of TiZrNb and TiZrNbHf. Their basic superconducting parameters, as the values of the critical temperature Tc, upper critical magnetic field Bc2 and the superconducting energy gap Δ have been studied with the use of magnetic susceptibility and point-contact Andreev reflection (PCAR) spectroscopy measurements. Although our samples have different critical temperatures, namely Tc ∼ 8.2 K for TiZrNb and Tc ∼ 6.3 K for TiZrNbHf, their zero-temperature critical magnetic field has the same value Bc2(0) = 12 T, from the vicinity of the Clogston limit. We have observed the presence of degraded phases on the surfaces of all the investigated samples using PCAR measurements. Still, we were able to show that the bulk phase in both systems exhibits BCS weakly coupled superconductivity with 2Δ(0)/kBTc ∼ 3.5.

Investigating Superconducting State Parameters in (TaNb)X(TiZrHf)1-X Compounds: A First Principle Approach Employing MS Excel as Toolkit

Investigating Superconducting State Parameters in (TaNb)_X(TiZrHf)_1-X Compounds: A First Principle Approach Employing MS Excel as Toolkit

Ab-initio insights into the physical properties of XIr3 (X = La, Th) superconductors: A comparative analysis

Here we report the structural, elastic, bonding, thermo-mechanical, optoelectronic and superconducting state properties of recently discovered XIr3 (X = La, Th) superconductors utilizing the density functional theory (DFT) using two different exchange-correlations functionals. The elastic, bonding, thermal and optical properties of these compounds are investigated for the first time. The calculated lattice and superconducting state parameters are in reasonable agreement to those found in the literature. In the ground state, both the compounds are mechanically stable and possess highly ductile character, high machinability, low Debye temperature, low bond hardness and significantly high melting point. The thermal conductivities of the compounds are found to be very low which suggests that they can be used for thermal insulation purpose. The population analysis and charge density distribution map confirm the presence of both ionic and covalent bonds in the compounds with ionic bond playing dominant roles. The calculated band structure and DOS profiles indicate metallic character of XIr3 compounds. It is also found from the DOS profile that the Ir 5d-states dominate near the Fermi level. Unlike the significant anisotropy observed in elastic and thermal properties, all the optical constants of XIr3 compounds exhibit almost isotropic behavior. The optical parameters’ profiles correspond very well with the electronic band structure and DOS features. We have estimated the superconducting transition temperature (Tc) of XIr3 compounds in this work. The calculated values of Tc for LaIr3 and ThIr3 compounds are 4.91 K and 5.01 K, respectively. We have compared and contrasted all the physical properties of XIr3 (X = La, Th) compounds in this study.

A comprehensive first-principles insights into the physical properties of binary intermetallic Zr3Ir compound

We have looked into the structural, mechanical, optoelectronic, superconducting state and thermophysical aspects of intermetallic compound Zr3Ir using the density functional theory (DFT). Many of the physical properties, including detailed direction dependent mechanical properties, hardness in different formalisms, Fermi surface topology, machinability, fracture toughness, optical properties, chemical bonding nature, and charge density distributions, are being investigated for the first time. According to this study, Zr3Ir exhibits ductile features, high machinability, significant metallic bonding, a small Vickers hardness with low Debye temperature, and a modest level of elastic anisotropy. Ductility, high level of machinability, and damage tolerance make this compound attractive for engineering applications. The mechanical and dynamical stabilities of Zr3Ir have been confirmed. The metallic nature of Zr3Ir is seen in the electronic band structures with a high electronic energy density of states at the Fermi level. The bonding nature has been explored by the charge density mapping and bond population analysis. Zr3Ir shows a remarkable electronic stability, as confirmed by the presence of a pseudogap in the electronic energy density of states at the Fermi level which is situated between the bonding and antibonding states. Energy dependent optical parameters show very good agreement with the electronic density of states profile. The reflectivity spectra reveal that Zr3Ir is a good reflector in the infrared and near-visible regions. Zr3Ir is an excellent ultra-violet (UV) radiation absorber. High refractive index at visible photon energies indicates that Zr3Ir could be used to improve the visual aspects of electronic displays. All the optical constants exhibit a moderate degree of anisotropy. Zr3Ir has a moderate melting point, high damage tolerance, and very low minimum thermal conductivity. The thermomechanical characteristics of Zr3Ir reveal that it is a potential thermal barrier coating material. The superconducting state parameters of Zr3Ir are also explored.

Effect of the Presence of Structural Defects on the Superconducting Properties of (NbTa)0.67(MoHfW)0.33 and Nb-47wt%Ti

A comparison of the results of studies on the influence of structural defects on the critical parameters of superconductivity has been made for the high-entropy alloy (NbTa)0.67(MoHfW)0.33 and for the conventional superconducting magnet material Nb-47wt%Ti. Positron annihilation lifetime spectroscopy (PALS), electrical resistivity, magnetization and magnetic susceptibility measurements were used. In addition, X-ray powder diffraction studies were performed on the high-entropy alloy (NbTa)0.67(MoHfW)0.33. Due to the rapid cooling of the materials after melting in the arc furnace, they contain a higher concentration of structural defects compared to the heat-treated materials. Magnetic property measurements showed that both the critical temperatures Tc and the upper critical fields μ0Hc2 of bulk superconductivity-related materials are improved in the presence of structural defects.

Statistics of the cuprate pairon states on a square lattice

In this paper the fundamental parameters of high-Tc superconductivity are shown to be connected to the statistics of pairons (hole pairs in their antiferromagnetic (AF) environment) on a square lattice. In particular, we study the density fluctuations and the distribution of the area surrounding each pairon on the scale of the AF correlation length , for the complete range of hole concentration. We show that the key parameters of the phase diagram, the Tc dome, and the pseudogap (PG) temperature , emerge from the statistical properties of the pairon disordered state. In this approach, the superconducting and the PG states appear as inseparable phenomena. The condensation energy, which fixes the critical temperature, is directly proportional to the correlation energy between pairons and not to the energy gap, contrary to conventional superconductors. When the correlation energy between pairons is suppressed by fluctuations, either thermally, by disorder, or in the vortex core, the PG state of disordered pairons is obtained. We attribute the unique features of cuprate superconductivity to this order–disorder transition in real space, which clearly differs from the Bardeen–Cooper–Schrieffer mechanism. Our predictions are in quantitative agreement with low-temperature tunneling and photoemission spectroscopy experiments.

The Study of Interplay of Singlet Superconductivity and Ferromagnetism in Superconducting HoMo6Se8

This article reports the effect of magnetic ordering and superconducting order parameter on superconducting and magnetic transition temperatures of interacting singlet superconductivity and ferromagnetism in HoMo6Se8 material. The basic superconducting parameters were calculated starting with the BCS type model Hamiltonian and using the double time temperature dependent Green function formalisms. Results showed that the superconducting critical temperature decreases with enhancement of superconducting order parameter and vice versa. This is perhaps due to the weakening of the binding energy as the temperature approaches its critical value. On the other hand, the superconducting critical temperature demonstrates attenuation with increasing magnetic order parameters . It was also observed that the enhancement of magnetic transition temperature with the increase of the magnetic order parameter demonstrates variation with the alteration of the superconducting order parameter. Moreover, the calculations revealed that there is a temperature region where both superconductivity and magnetic order coexist. Furthermore, the present theoretical analysis is broadly in agreement with existing experimental findings.

Electron-phonon coupling in La3In under pressure

Conventional superconducting parameters Eliashberg spectral function, phonon DOS, average electron-phonon coupling constant & superconducting transition temperature of La3In were calculated at ambient and applied positive hydrostatic pressure. Ambient pressure electron-phonon coupling constant was found to be 1.43 and superconducting transition temperature was calculated to be 8.7 K which is close to the experimental reported value of 9.5 K. Logarithmic average phonon frequency at ambient pressure was found to be 6.21 × 10−3 eV. Phonon dispersion relations for the ambient and applied positive hydrostatic pressure were calculated to confirm the dynamical stability of La3In under positive pressure. Acoustic modes of vibrations were found to mediate most of the electron-phonon-electron interaction with a very small contribution from optical modes of vibrations. Fermi surface at ambient pressure was also calculated and employed in explaining the large value of the calculated electron-phonon coupling constant. The effect of spin–orbit coupling on electronic, phonon and superconducting properties of La3In was also studied.

Scanning Intrinsic Superconductivity and the Spin Hall Effect in Niobium Borides

Although niobium borides have been extensively studied on their mechanical properties, a systematic investigation on their potential metastable phases, superconducting excitations, and spin Hall effects (SHE) is still lacking. Herein, we carry out a global structure search in the Nb-B system based on the evolutionary algorithm and density functional theory. Thermodynamical, dynamical, mechanical, and quasiharmonic approximation investigations unveil four new phases, Nb3B5, Nb2B5, Nb3B7, and Nb5B4, which are promising candidates for experimental preparations. Moreover, the superconducting transitions of all Nb-B compounds are performed from electron–phonon calculations. In addition, all Nb-B compounds are predicted to be topologically nontrivial. More intriguingly, Nb2B5 is unveiled as a promising noncentrosymmetric superconductor to explore topological superconducting excitation. Furthermore, nonzero spin Hall conductivity (SHC) tensor elements of all Nb-B compounds are predicted, and NbB is predicted to own a maximal SHC value of 320 (ℏ/e) (S/cm) among all Nb-B compounds. Our theoretical results fill in the gap on superconducting and SHC parameters of Nb-B binaries, demonstrating that Nb-B binaries are a potential choice to explore superconducting excitations and topological states and to investigate the SHE.

Superconducting properties of the A15 structure compound V[formula omitted]Ge

Applications of A15 superconductors have received considerable attention, resulting in a large body of reported research work on A15 superconductors. Nonetheless, studies on this material focusing on its superconducting parameters are scarce. This motivates new efforts toward bulk measurements in typical A15 material V3Ge, which is also the isomorph of V3Si with a superconducting transition temperature at 17 K. In this study, we determined the superconducting parameters of single-phase V3Ge crystals, which crystallize in the A15 structure, through measurements of magnetization, magnetic susceptibility, electrical resistivity, and heat capacity. Our results show that the temperature (Tc) of its superconducting transition is 6.2±0.4 K. Moreover, we conducted electrical resistivity and magnetic susceptibility measurements and found the lower and higher critical fields to be 559 Oe and 39.8 kOe, respectively. The Ginzburg–Landau parameter κGL is determined to be 9.78, which is much greater than 1/2, implying V3Ge Type-II superconductor. The Sommerfeld coefficient γ in the normal state is determined to be 31.2 mJ/K2 mol, which is 50∼100 folds higher compared to that in the normal metal, thereby indicating the enhancement of the density of state at the Fermi energy. The Debye temperature Θ is estimated to be 430 K, and the value of the drastic increase in the specific heat at Tc is approximately 1.33, which is 7% smaller than the weak coupling limit of 1.43 predicted by the Bardeen–Cooper–Schrieffer (BCS) theory. The electron–phonon coupling constant λe−ph is 0.61. These values suggest that V3Ge is a conventional superconductor with s-wave symmetry in the BCS framework, which implies that the high Debye temperature and large density of states at the Fermi energy contribute to the increase in Tc in V3Ge. The superconducting parameters determined in this study provide guidance for the development of a new metal superconductor with high-Tc.

The structural, magnetic, and pinning features of Bi-2223 superconductors: Effects of SiC nanoparticles addition

In this research, the influence of Silicon Carbide nanoparticles (SiC-NPs) addition on the microstructure, superconducting, and pinning properties of (Bi, Pb)2Sr2Ca2Cu3O10+θ (Bi-2223) superconductors is comprehensively studied. The superconductors are synthesized by the sol-gel method and SiC-NPs are added up to 0.8 wt%. The X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) measurements are carried out for structural and morphological investigations. The superconductivity parameters such as intra-granular critical current density (JC, intra), inter-granular current critical density (JC, inter), transport critical current density (JC, t), and pinning force density (FP) are detected through DC- and AC-susceptibility, hysteresis loop, and transport measurements. The obtained results show that the 0.4 wt% addition of SiC-NPs improves the microstructure and the connectivity of grains as well as JC, inter, JC, intra, JC, t, and FP in the Bi-2223 superconductor. This research opens notable avenues for the use of synthesized Bi-2223 ceramics for electrical and industrial applications such as high-current energy storage, wires, and tapes.

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 that directly manifests the Cooper pair bulk density in the material. Although this field can be measured using several techniques, the most conventional method is to calculate this field from the 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, we found no mathematical routine that describes how this starting point of deviation can be found. Here, we propose the extraction of Bp from the fit of the 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: the power-law exponent. We demonstrated the applicability of this approach to polycrystalline ThIr3, WB4.2, BaTi2Bi2O, and Th4H15; thin films of Pb and MgB2; and Nb single crystal. In most reports, Bc1(T) analysis is limited by the extraction of the London penetration depth. 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, ΔCγTc; and the gap-to-transition temperature ratio, 2Δ0kBTc] from Bc1(T) data. This extraction was performed for Nb, ThIr3, TaRh2B2, and NbRh2B2.

The effect of sintering conditions on the superconducting properties of melanin doped MgB2

In this work, the melanin-doped MgB2 samples were prepared under the same condition at different sintering temperatures. The XRD quantitative analysis indicates an increase in crystallite size with increasing sintering temperature. The pinning mechanism tends to be a collective of surface and point pinning in an indication of the role of the impurities and secondary phases in the forming of flux pinning centers. The electrical and magnetic measurements show significant enhancement on critical current density obtained from the doped samples compared to the pure ones. Enhancing critical current density and critical fields depend on the sintering conditions. Sintering at low-temperature results in a high critical current density and critical field values. The resistivity and the related superconducting parameters measurements were also completed.

Experimental and first-principles studies on superconductivity in noncentrosymmetric La3Se4

We report the synthesis and detailed characterization of superconducting ${\mathrm{La}}_{3}{\mathrm{Se}}_{4}$, with ${T}_{c}\ensuremath{\sim}8.5\ifmmode\pm\else\textpm\fi{}0.1$ K, using x-ray diffraction, electrical transport, magnetization, and heat capacity measurements. ${\mathrm{La}}_{3}{\mathrm{Se}}_{4}$ crystallizes in the noncentrosymmetric cubic ${\mathrm{Th}}_{3}{\mathrm{P}}_{4}$-type structure with space group $I\overline{4}3d$. Characteristic superconducting parameters such as the lower critical field, upper critical field, thermodynamic critical field, coherence length, penetration depth, and Ginzburg-Landau parameter have been determined. The specific heat jump at ${T}_{c}$, $\mathrm{\ensuremath{\Delta}}C/\ensuremath{\gamma}{T}_{c}=2.04\ifmmode\pm\else\textpm\fi{}0.05$, exceeds the value for a weakly coupled BCS superconductor, and the electron-phonon coupling constant is found to be ${\ensuremath{\lambda}}_{ep}=0.87\ifmmode\pm\else\textpm\fi{}0.02$, suggesting superconductivity in ${\mathrm{La}}_{3}{\mathrm{Se}}_{4}$ is in the strong-coupling regime. The estimated upper critical field is well below the calculated Pauli limit, and the Maki parameter value ($\ensuremath{\alpha}<$ 1) indicates that the superconducting upper critical field is dominated by orbital pair breaking. From density functional theory based first-principles simulations we observe the number of states at the Fermi energy is dominated mainly by $d$ and $f$ electrons of La. Furthermore, we observe band crossings along the high-symmetry $k$ lines in the vicinity of the Fermi energy. These bands are observed to split due to the removal of spin degeneracy associated with spin-orbit coupling, with the splitting energy ${E}_{\mathrm{ASOC}}\ensuremath{\approx}$ 65 meV.

Theoretical study of superconducting parameters of Al and Li Co-doping substitution on MgB2

In the present study we investigated the theoretical calculation of Superconducting state parameters by Al as electron doping and Li as hole co-doping on MgB2 superconductor for four different concentrations (Mg0.962Al0.018Li0.02B2, Mg0.854Al0.096Li0.05B2, Mg0.812Al0.138Li0.05B2, Mg0.77Al0.14Li0.09B2). The well-known Empty Core (EMC) model of Ashcroft potential was used to study the theoretical investigation of the superconducting state parameters (SSP) viz. Electron–Phonon Coupling Strength (λ), Coulomb Pseudopotential (µ*), Transition Temperature (Tc), Isotope Effect Exponent (α) and Effective Interaction Strength (N0V) of Mg1-x-yAlxLiyB2 system. It is observed that addition of Al & Li doping to superconductor MgB2 causes the parameters λ, Tc, α and N0V decreases. This suggests decrease in superconducting behaviour of MgB2 is due to effect of Al and Li co-doping in MgB2 which also shows strong coupling to intermediate coupling behaviour. Whereas Coulomb Pseudopotential (µ*) remains approximately same. In this paper it is also observed that Transition Temperature (Tc) for Mg1-x-yAlxLiyB2 alloys for different concentration is almost same with the experimental values.

Experimental study of elements of a Josephson traveling-wave parametric amplifier on SQUID chains.

The issues of designing a Josephson traveling-wave parametric amplifier (JTWPA) based on a well-established technology of superconducting microcircuits with given and controlled parameters based on high-quality Nb-AlOx-Nb tunnel junctions are considered. This technology has been adapted and optimized to obtain structures with the required parameters and circuits with large number of tunnel junctions. To advance the technology, the basic elements of a promising JTWPA have been devel-oped, manufactured and studied. In direct current measurements, a number of super-conducting elements parameters were experimentally determined; these parameters are required for designing a JTWPA chips for microwave measurements. An original design of JTWPA based on a chain of SQUIDs in a coplanar line has been developed for implementation using the IRE niobium technology; the parameters of the main elements of the JTWPA have been determined. Keywords: Josephson travelling-wave parametric amplifiers (JTWPA), Josephson metamaterials (JMM), Josephson junctions (JJs), cold amplifier, coplanar lines, quantum noise, SIS, SQUIDs.

Экспериментальное исследование элементов джозефсоновского параметрического усилителя бегущей волны на цепочке СКВИДов

The issues of designing a Josephson traveling-wave parametric amplifier (JTWPA) based on a well-established technology of superconducting microcircuits with given and controlled parameters based on high-quality Nb-AlOx-Nb tunnel junctions are considered. This technology has been adapted and optimized to obtain structures with the required parameters and circuits with large number of tunnel junctions. To advance the technology, the basic elements of a promising JTWPA have been devel-oped, manufactured and studied. In direct current measurements, a number of super-conducting elements parameters were experimentally determined; these parameters are required for designing a JTWPA chips for microwave measurements. An original design of JTWPA based on a chain of SQUIDs in a coplanar line has been developed for implementation using the IRE niobium technology; the parameters of the main elements of the JTWPA have been determined.

Investigation of the superconducting properties of NbN films deposited by DC magnetron sputtering on a high-k dielectric HfO2 buffer layer

The influence of the buffer layer of hafnia dielectric (HfO2) on the superconducting properties of niobium nitride films (NbN), produced by the technique of reactive magnetron depositing has been investigated for the first time. This study presents a comprehensive analysis of morphological, microstructural, and electrophysical parameters of thin NbN films. The dependence of transition critical temperature on the thickness of the HfO2 buffer layer has been obtained. For the first time, it has been demonstrated that the superconducting properties of niobium nitride films at the HfO2 buffer layer have high superconductive parameters, namely, T c ∼ 13 K (with a the film thickness of approximately 30 nm) and high critical current density of approximately 107 A cm−2. The relation between the thickness of the HfO2 buffer layer with the critical current density of niobium nitride films has been determined. It appeared that the values of critical current density increase significantly up to 13 MA cm− 2 when the thickness of the hafnia buffer layer is more than 2 nm.

SnAs: A 4K weak type-II superconductor with non-trivial band topology

Superconductors with non-trivial band topology are emerging as one of the best avenues to study quantum anomalies and experimental realization of Majorana Fermions. This article reports the successful crystal growth of superconducting SnAs, which can have topologically non-trivial states, as evidenced in DFT (Density Functional Theory) calculations, Z2 invariants and topological surface states. Here, we followed a two-step method to grow SnAs crystal. The powder XRD (X-ray Diffractometry) pattern of synthesized crystal ensures that the crystal is grown in a single phase with a NaCl type cubic structure and the EDAX (Energy Dispersive X-ray Analysis) endorses the stoichiometry of the as-grown sample. The DFT calculations performed with and without inclusion of spin-orbit coupling (SOC) show band inversion at various k symmetry points near the Fermi level. The recorded Raman spectra show two different modes, which are assigned as A1 and ETO vibrations. The ZFC (Zero-Field Cooled) & FC (Field Cooled), as well as the isothermal M − H (Magnetization vs. field) measurements, are also performed for the topological non-trivial SnAs superconductor, which eventually confirm the weak type-II superconductivity at 4K. Various other superconductivity parameters viz. kappa parameter, coherence length, and penetration depth are also calculated to probe the as-grown sample's characteristics.