Aslamazov-Larkin Research Articles

Excess Conductivity Analysis of an YBCO Foam Strut and Its Microstructure.

Struts of a superconducting YBa2Cu3Oy (YBCO) foam prepared by the infiltration growth method on the base of commercial polyurethane foams were extracted from the bulk, and thoroughly characterized concerning the microstructure and the magnetoresistance, measured by the four-point technique. Optical microscopy, electron microscopy, electron backscatter diffraction and atomic force microscopy observations indicate a unique microstructure of the foam struts which shows a large amount of tiny Y2BaCuO5 (Y-211) particles (with diameters between 50 and 100 nm) being enclosed in channel-like grain boundaries between the YBCO grains and a one-of-a-kind surface of the struts covered with Ba3Cu5Oy-particles. The resistance data obtained at temperatures in the range 4.2 K ≤T≤ 150 K (applied magnetic fields ranging from 0 to 7 T) were analyzed in the framework of the fluctuation-induced conductivity (FIC) approach using the models of Aslamazov-Larkin (AL) and Lawrence-Doniach (LD). The resulting FIC curves reveal the presence of five distinct fluctuation regimes, namely, the short-wave (SWF), one-dimensional (1D), two-dimensional (2D), three-dimensional (3D), and critical (CR) fluctuation domains. The analysis of the FIC data enable the coherence length in the direction of the c-axis at zero-temperature (ξc(0)), the irreversibility field (Birr), the upper critical magnetic field (Bc2), the critical current density at T= 0 K (Jc(0)) and several other parameters describing the the material's superconducting properties to be determined. The present data reveal that the minuscule Y-211 particles found along the YBCO grain boundaries alter the excess conductivity and the fluctuation behavior as compared to conventional YBCO samples, leading to a quite high value for Jc(0) for a sample with a non-optimized pinning landscape.

YBCO polycrystal co-added with BaTiO3 and WO3 nanoparticles: Fluctuation induced conductivity and pseudogap studies

We report the effect of the addition of BaTiO3 and WO3 nanoparticles on the pseudogap and excess conductivity of YBCO polycrystal. The excess conductivity analysis showed that the experimental data of pure and sample added with low amount of WO3 and BaTiO3 were perfectly described by the 2D Maki-Thompson (MT) and 3D Aslamazov-Larkin (AL) models. A sharp decrease in excess conductivity was obtained for samples added with high amount of nanoparticles where the analysis indicated the presence of the AL contribution and Lawrence-Doniach (LD) models. The pseudogap (PG) results showed that the value of Tpair (the temperature at which local pairs are transformed from strongly bound bosons into the fluctuating Cooper pairs) increased from around 117 K for the pure sample to around 187 K for sample co-added with low amount of nanoparticles. The pseudogap Δ*(TG) reduced from 230.9 K (for pure sample) to 223.4 K (for added sample).

STRUCTURAL AND MAGNETO CONDUCTIVITY STUDIES OF NIO/SMBA2CU3O7-Δ SUPERCONDUCTING COMPOSITE

In this work, we investigate the effect of NiO nanoparticles' addition on the structure, superconductivity, and magneto conductivity for the SmBa2Cu3O7-δ phase. Composite nano/superconductor of (NiO)x/SmBa2Cu3O7-δ (0.00≤x≤0.12 wt.%) were prepared by conventional solid-state reaction technique and characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The orthorhombic structure was maintained whereas the lattice parameters showed unsystematic variations with the NiO nanoparticles addition. The superconducting transition temperature Tc, determined from electrical resistivity measurements, showed an enhancement with x up to 0.04wt.% followed by a reduction with higher NiO additions. The Aslamazov–Larkin (AL) model was employed to analyze the magneto conductivity. The model allowed to determine the coherence lengths along c-axis ξc(0) and along ab plane ξab(0). Moreover, the anisotropy parameter Г increase with the increase of NiO nanoparticles addition.

Fluctuation magnetoconductivity in superconducting Ca10(Pt4As8)(Fe2As2)5 single crystal

Fluctuation-induced conductivity up to μ0H = 14 T for superconducting Ca10(Pt4As8)(Fe2As2)5 single crystal was evaluated from the measured in-plane electrical resistivity, and it was analyzed by Aslamazov-Larkin (AL) theory for zero magnetic field and Ullah and Dorsey (UD) scaling method for magnetic field. A dimensional crossover of superconducting fluctuations from low-temperature three-dimension to high-temperature two-dimension was observed. When the dimensional crossover occurs, a temperature region in which two-dimensional and three-dimensional fluctuations occur simultaneously was found in the intermediate temperature region.

Infrared Spectroscopy and Excess Conductivity Analysis for (Y3Fe5O12)x/Cu0.5Tl0.5Ba2Ca2Cu3O10-δ Composites

In this study, the influence of adding Yttrium iron garnet (Y3Fe5O12) nanoparticles (NPs) on the microstructure and fluctuation-induced conductivity (FIC) of Cu0.5Tl0.5Ba2Ca2Cu3O10-δ (CuTl-1223) superconductor was studied. Y3Fe5O12 NPs were produced by the co-precipitation technique. By solid state route, (Y3Fe5O12)x/Cu0.5Tl0.5Ba2Ca2Cu3O10-δ composites, with x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10 wt. % were prepared. The tetragonal unit cell parameters of (Y3Fe5O12)x/Cu0.5Tl0.5Ba2Ca2Cu3O10-δ composites were found to be invariable with Y3Fe5O12 content. The volume fraction of the host phase was increased with Y3Fe5O12 addition till x = 0.04 wt. %. The different vibrational modes of the samples were identified through Fourier transform infrared spectroscopy (FTIR). The transition from normal to the superconducting state, for the prepared composites, was done through d.c resistivity measurements from room temperature down to zero critical temperature (T0). The Aslamazov–Larkin (AL) model was used to examine fluctuation regions in resistivity-temperature curves. At high temperatures, short wave fluctuation was observed. A cross-over between short wave fluctuation and the mean-field region was spotted at lower temperatures. The mean field region for the examined composites was composed of two-dimensional fluctuations along with one-dimensional fluctuation. The coherence length along the c-axis ζc(0), interlayer coupling (J), and anisotropy parameter (γ) were estimated from the Lawrence–Doniach (LD) model as a function of Y3Fe5O12 content.

Excess Conductivity Analyses in Bi-Pb-Sr-Ca-Cu-O Systems Sintered at Different Temperatures

This paper studies the effects of the sintering temperature on crystal structure, critical temperature (Tc) and excess conductivity of Bi-Pb-Sr-Ca-Cu-O (BPSCCO) system. Bulk BPSCCO samples were fabricated by the solid-state reaction method. Four different temperatures of 835 °C, 840 °C, 845 °C, and 850 °C were applied to sinter four different samples. The crystal structure of the samples was investigated through X-ray diffraction measurements (XRD) and scanning electron microscopy (SEM). Superconductivity of the samples was analyzed by the temperature-dependent resistivity measurement. The experimental results showed the existence of both Bi-2223 and Bi-2212 phases in all samples. Quantitatively, the volume fraction of the Bi-2223 phase was found to increase from 53.56% to 75.97%, and the average grain size of Bi-2223 phase was observed to enlarge from 57.95 nm to 86.50 nm as the sintering temperature increased from 835 °C to 850 °C. In addition, the excess conductivity analyses based on the theory of Aslamazov - Larkin (AL) and Lawrence - Doniach (LD) showed decreases in the coherence lengths (ξc(0)) from 1.957 Å to 1.565 Å and the effective inter-layering spacing (d) from 79.7 Å to 64.5 Å. Meanwhile, the interlayer coupling strength (J) between two CuO2 planes was estimated to increase from 0.00083 to 0.00137. These results might be evidence to conclude that the increasing of the sintering temperature obviously improves the superconductivity in the BPSCCO system.
 

Fluctuating Cooper pairs in FeSe at temperatures exceeding double T c

Temperature dependencies of excess conductivity, , have been studied in detail for three FeSe0.94 textured polycrystalline samples prepared by partial melting and solid state reaction. It was revealed that both and its temperature dependence are extremely sensitive to the method of sample preparation. Then, it was shown that in the range from the superconducting transition temperature T c ~9 K up to the characteristic temperature T 01 ~19 K, obeys the classical fluctuation theories of Aslamazov–Larkin (AL) and Hikami-Larkin (Maki-Thompson (MT) term) pointing to the existence of fluctuating Cooper pairs in FeSe at temperatures exceeding double T c . Like in cuprates, AL–MT crossover at is observed, which means the appearance of 3D–2D dimensional transition at this temperature. This allows us to determine the coherence length along the c-axis, ξ c (0) ~3 Å, and a set of additional samples’ parameters, including the phase relaxation time, , of fluctuating Cooper pairs (FCPs), within a simple two-dimensional free-carrier picture. It was shown that in FeSe coincides with that found for YBa2Cu3O suggesting that the nature of superconducting fluctuations is very similar for these high-temperature superconductors of different types.

Dimensionality and superconducting parameters of YBa2Cu3O7−d/(WO3 NPs)x composites deduced from excess conductivity analysis

Superconducting composite products of type YBa2Cu3O7−d (noted Y-123) added with different contents (x wt.%) of tungsten oxide nanoparticles (WO3 NPs), x = 0.0–1.0 wt%, were produced via the standard solid-state reaction technique. Samples were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and electrical resistivity measurements. XRD examination showed that the Y-123 orthorhombic structure is not altered by WO3 NPs additions. SEM observations indicated a reduction in the grains size with the increase of nanoparticles content. The investigation of the excess conductivity of different prepared composites was analyzed using Aslamazov-Larkin (AL) model. The investigated samples comprised of five distinct fluctuation regimes, namely short-wave (SWF), one-dimensional (1D), two-dimensional (2D), three-dimensional (3D), and critical (CR) fluctuations regimes. The coherence length along c-axis at zero-temperature (ξc(0)), lower and upper critical magnetic fields (Bc1 and Bc2), critical current density (Jc) and numerous other superconducting parameters were estimated with respect to WO3 NPs content. Compared to undoped Y-123 sample, it was found that an amount of x = 0.05 wt% of WO3 NPs is appropriate to improve the physical performances of Y-123, whereas with further increasing x, these performances were weakened.

Excess conductivity investigations of WO3 nanowires added to YBa2Cu3O7-d superconductor

Series of YBa2Cu3O7-d + x wt% WO3 nanowire mixtures where x = 0.0–2.0 wt% were prepared via solid-state reaction method. X-ray diffraction (XRD) patterns show the unaffected orthorhombic structure in various composites. Scanning electron microscopy (SEM) micrographs show the increase in grains size and the filling of voids between grains by WO3 nanowires. The superconducting transition temperatures deduced from electrical resistivity versus temperature (ρ(T)) measurements are almost unchanged by lower WO3 nanowires addition (i.e., x 0.5 wt%). The analysis of excess conductivity fluctuation (∆σ) by means of Aslamazov–Larkin (AL) and Lawrence–Doniach (LD) approaches was investigated. Dimensional fluctuations, coherence lengths, effective layer thickness, zero temperature lower and upper critical magnetic fields (Bc1 (0) and Bc2 (0)), and critical current density at temperature T = 0 K (Jc(0)) were extracted and discussed in relation with the structure and morphology. Improvements in Bc1 (0), Bc2 (0), and Jc(0)) were noticed for samples added with lower WO3 nanowires content, particularly for x = 0.1 wt% composite sample.

Electrical properties and fluctuation induced conductivity studies of Bi-based superconductors added by CuS nanoparticles synthesized through the aqueous route

The effect of copper sulfide (CuS) nanoparticles synthesized by aqueous route on the electrical transport and on the fluctuation induced conductivity of polycrystalline (Bi,Pb)2Sr2Ca2Cu3Oy (denoted Bi-2223) was reported. The global critical current densities versus temperature, Jct(T), at self and applied magnetic field was analyzed within the collective pinning model. The electrical resistivity versus temperature, ρ(T), above the mean-field temperature Tc was analyzed using Aslamazov-Larkin (AL) and Lawrence-Doniach (LD) models. Different fluctuation regimes indicated by short-wave region (SWR), three-dimensional (3D), two-dimensional (2D), one-dimensional (1D), and critical region (CR) fluctuations were identified. The zero-temperature coherence length, the effective layer thickness, the critical magnetic fields, and the critical current densities are determined. It was found that samples sintered with an additional amount of CuS nanoparticles (< 0.4 wt%) exhibit higher upper critical magnetic fields and critical current densities compared to the pure one and the highest values of these parameters are obtained in the 0.2 wt% CuS added sample. Consequently, the addition of CuS nanoparticles could introduce strong pinning centers that contribute to the decrease of magnetic vortex motion which enhances the flux pinning capacities and the transport abilities inside the Bi-2223 system.

Features of Excess Conductivity Behavior in a Magnetic Superconductor Dy0.6Y0.4Rh3.85Ru0.15B4

The temperature dependencies of the excess conductivity σ′(T) and possible pseudogap (PG), Δ*(T), in a Dy0.6Y0.4Rh3.85Ru0.15B4 polycrystal were studied for the first time. It was shown that σ′(T) near Tc is well described by the Aslamazov–Larkin (AL) fluctuation theory, demonstrating a 3D–2D crossover with increasing temperature. Using the crossover temperature T0, the coherence length along the c axis, ξc(0), was determined. Above the level of T2D &amp;gt; T0, an unusual dependence σ′(T) was found, which is not described by the fluctuation theories in the range from T0 to TFM, at which a ferromagnetic transition occurs. The range in which superconducting fluctuations exist is apparently quite narrow and amounts to ΔTfl ≈ 2.8 K. The resulting temperature dependence of the PG parameter Δ*(T) has the form typical of magnetic superconductors with features at Tmax ≈ 154 K and the temperature of a possible structural transition at Ts ∼ 95 K. Below Ts, dependence Δ*(T) has a shape typical for PG in cuprates, which suggests that the PG state can be realized in Dy0.6Y0.4Rh3.85Ru0.15B4 in this temperature range. Comparison of Δ*(T) with the Peters–Bauer theory made it possible to determine the density of local pairs near Tc, 〈n↑n↓〉(TG) ≈ 0.35, which is 1.17 times greater than in optimally doped YBa2Cu3O7–δ single crystals.

Enhanced coherence length and interplane coupling by Ti doping in (Cu, Tl)-1223 superconductors: Para conductivity analyses

The fluctuation induced conductivity (FIC) analyses of Ti doped (Cu0.5Tl0.5)Ba2(Ca2-xTix)Cu3O10-δ superconducting samples have been carried. Aslamazov-Larkin (AL) and Lawrance-Doniach (LD) models were used to study the FIC in the critical, 3D, 2D and 0D regions. Maki-Thompson (MT) model has been employed to study the effect of the Cooper-pairs on the normal electrons. From these analyses the coherence length along the c-axis, ξc (0), the inter-plane coupling constant, J, the phase relaxation time, τφ , Fermi velocity, VF, and the energy essential for breaking apart the Cooper's pairs, E, are determined. From the cross-over temperature, TG, of critical to 3D regime the Ginsberg number, NG, has been calculated. Using NG and the Ginsburg–Landau (GL) equations, various important parameters like thermodynamic critical magnetic field, Bc(0), the lower critical field, Bc1(0), the upper critical field, Bc2(0), the critical current density, Jc (0), as well as the penetration depth, λp.d, have been calculated. Values of Tc, TG, Tcmf, ξc(0) and J are increased with the increasing Ti contents. All the fluctuation regimes have been shifted to higher temperature and the anisotropy is reduced with the doping of Ti. Also VF and E are found to enhance with Ti doping while the phase relaxation time is reduced. The most probable reason for all these improved parameters is the smaller ionic radius of Ti atom, which brings the CuO2 planes closer together thereby enhancing the density of Cooper pairs in the unit cell. The values of Bc(0), Bc1(0), and Jc(0) are suppressed while the values of λp.d and κ are increased with increased Ti contents. The suppression in the critical fields and current density may be attributed to the decrease in the free energy difference of the normal and superconducting states.

Conductivity Fluctuation and Some Parameters of High temperature Superconductor Polycrystalline Y1Ba2Cu3O7−δ doped with Silver Nanoparticles

In this study, we report the effect of Ag nanoparticles doping on the dimensional fluctuations of superconducting order parameters, crystal structure, and some parameters of Y1Ba2Cu3O7−δ + × Ag (x = 0.0, 0.06, 0.1, 0.3, and 0.6 wt%) polycrystalline ceramics. By increasing the content of Ag in YBCO matrix, X-ray diffraction (XRD) with the Rietveld refinement technique revealed that the crystal lattice parameters changed and the orthorhombicity decreased slightly. Also, the increase of Ag wt% caused a decrease of superconducting transition temperatures (Tc) which are determined from the standard four-probe method and dropped abruptly. Aslamazov–Larkin (AL) model was used to analyze excess conductivity fluctuation. Lawerence–Doniach (LD) temperature named TLD which is responsible for the dimensional nature of fluctuation inside the grains is influenced by nano-silver combination in the compound. Crossover temperature from 2D to 3D (TLD) decreased in the mean-field region as a resultant dominance of 3D region by increasing of Ag in YBCO matrix. The decrease in zero-resistance critical temperature (Tc zero), zero-temperature coherence length along the c-axis ξc(0), and super layer length d values implies the degradation of inter-grain weak links, more disorder state of samples and unsettling of the mean free path for the charge carriers respectively with addition of silver nanoparticles. The calculations based on AL and LD model showed the highest anisotropy (γ = 1.34681) for the x = 0.6 sample. The size of the Ag ions, being larger compared to Cu ions, and the number of substitution sites affects the coupling between the CuO2 planes and that results in higher anisotropy. Critical magnetic fields Bc1(0), Bc2(0), and critical current density Jc(0) were indirectly calculated from the Ginzburg–Landau (GL) number and GL equations. By increasing the doping level of silver nanoparticle, these parameters were found to be higher in Ag-added YBCO samples compared to the pure Y123, meaning better intrinsic flux pinning properties of doped Y123. The silver nanoparticle inclusion reduces the grain size and increases the strength and hardness of the parent compound.

Role of interlayer coupling in alkaline-substituted (Bi, Pb)-2223 superconductors

In this work, we investigated a correlation between superconductivity and interlayer coupling of two different alkaline (Na and K)-substituted Bi1·6Pb0·4Sr2Ca2Cu3O10+δ (BSCCO) polycrystalline samples. The excess conductivity analysis by the Aslamazov-Larkin (AL) and Lawrence-Doniach (LD) theories showed that Na substitution at the Ca site induced a gradual broadening of 3D fluctuation region with increasing interlayer coupling strength, which explains a systematic increase of Tc and a decrease of normal state resistivity. On the other hand, exactly the opposite results were observed in the K-substituted samples in place of Sr. Extended x-ray absorption fine structure (EXAFS) studies revealed that substitution of Na and K generated completely different effects on the local structure around Cu atoms. It is noticeable that the Cu–O bond distance was found to decrease monotonically with the varying amounts of Na, which indicates that the CuO2 layer is stabilized. On the while, the opposite was observed to occur with the varying amounts of K. Unlike the Cu–Ca bond which was the least affected by the substitution, the Cu–Sr bond distance increased drastically with K substitution. All these findings indicate that Na substitution at the Ca site enhances superconductivity with no loss of interlayer interaction, while K substitution at the Sr site weakens superconductivity due to the diminished interlayer interaction.

Robust superconductivity against the antiferromagnetic ordering in Pr2Pt3Ge5

The polycrystalline sample of Pr2Pt3Ge5 have been prepared successfully. The temperature and magnetic field dependence of resistivity as well as heat capacity has been carried out. The resistivity reveals the robustness of superconductivity against intrinsic antiferromagnetic ordering in the system. The onset of superconducting phase transition, TCon ≈ 6.7 K and the two antiferromagnetic transitions at TN1 ≈ 3.5 K and TN2 ≈ 4.3 K are almost similar to its single crystal counterpart. Important superconducting as well as normal state parameters have been estimated and discussed. Hc2(0) ≈ 2.5T as estimated using Werthamer-Helfand-Hohenberg (WHH) formalism while Hc2(0) ≈ 2.1T by using Ginzburg-Landau (GL) theory. The Hc2(0) value is quite high as compared to its single crystal counterpart. The reason could be the formation of pinning centers hitherto unknown. The broadening of resistivity curves with the increment of magnetic field has been analyzed using the thermally activated flux flow of vortices (TAFF) model whereas the zero field broadening is analyzed in terms of Aslamazov-Larkin (AL) predictions. From TAFF analysis the activation energy (U0) has been determined. The normal state magnetoresistance at different isothermal conditions doesn't obey the Kohler's rule, which reveals the possibility of an anisotropic Fermi surface and/or the multiband nature of the system. The specific heat measurement doesn't show substantiate jump at superconducting temperature similar to the single crystal counterpart. As we increase the magnetic field, the antiferromagnetic peaks get suppressed and completely vanishes around 10T.

Effect of Cr Substitution on the Formation and Fuctuation-Induced Conductivity Analysis of (Tl&lt;sub&gt;1-x&lt;/sub&gt;Cr&lt;sub&gt;x&lt;/sub&gt;)Sr&lt;sub&gt;2&lt;/sub&gt;CaCu&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt; Superconductor

The (Tl1-xCrx)Sr2CaCu2O7 (Tl-1212) sample with nominal starting composition for x = 0.0, 0.2 and 0.3 were prepared by the solid-state reaction method. The samples were studied by powder x-ray diffraction method and electrical resistance versus temperature measurement. Excess conductivity analysis was carried out using the Aslamazov–Larkin (AL) theory, and the dimension of fluctuation-induced conductivity (λ) was determined. The Lawrence–Donaich (LD) theory was used to calculate the coherence length (ξc(0)), Josephson coupling (J), and γ = (ξab(0)/ξc(0)) of the superconductive samples. Excess conductivity analysis showed that Cr substitution induced 2D-to-3D conductivity transition at the highest transition temperature (T2D-3D) observed at x = 0.3. The calculations based on the Lawrence–Doniach model revealed that the shortest coherence length and weakest inter-plane coupling (J) occurred when x = 0.2. The sample with x = 0.2 and 0.3 showed the Tl-1212 as the major phase. The highest onset temperature of 110 K was observed in the x = 0.2 sample. Our result showed that the formal value of 2.3+ is more important than the Josephson interlayer coupling J in optimizing the transition temperature.

Intersecting Aslamazov–Larkin and hopping conduction in superconducting RE-123

The coherence lengths of three superconductors have been extracted in the framework of Aslamazov–Larkin (AL) equation. A superconductor with an upturn in the normal state is found to have a very high coherence length in comparison to that of the two others with metallic normal states. We have suggested that an approximated Aslamazov–Larkin (AL) equation can be used to express the resistivity as a function of temperature in the paracoherent region. Our suggested form for ρAL (T) has been compared with the experimental resistivity ρ(Τ) to extract the coherence length in NBCO. An intersection of the suggested ρAL (T) and the variable range hopping (VRH) conduction ρVRH (T) has been observed to be sensitive to the coherence length. The ratio of the localization length and the coherence length is found to be very effective in shifting of crossing point towards the onset critical temperature in NBCO.

Effect of nano BiPb-2212 phase addition on BiPb-2223 phase properties

BiPb-2212 phase in nanoscale was added to BiPb-2223 phase with a general stoichiometry of (Bi[Formula: see text]Pb[Formula: see text]Sr[Formula: see text]Ca[Formula: see text]Cu[Formula: see text]O[Formula: see text]/Bi[Formula: see text]Pb[Formula: see text]Sr[Formula: see text]Ca[Formula: see text]Cu[Formula: see text]O[Formula: see text], 0.0 [Formula: see text] x [Formula: see text] 2.5 wt.%. All samples were prepared by the standard solid-state reaction method. The prepared nano BiPb-2212 phase was characterized by X-ray powder diffraction (XRD) and transmission electron microscope (TEM). The prepared samples were characterized by XRD and the scanning electron microscope (SEM). XRD analysis indicated that the sample with x = 1.5 wt.% has the highest relative volume fraction for BiPb-2223 phase. Samples were examined by electrical resistivity and I–V measurements. There is no significant change in the superconducting transition temperature [Formula: see text] for all samples. The highest critical current density [Formula: see text] was recorded for the sample with x = 1.5 wt.%. The normalized excess conductivity [Formula: see text] was calculated according to Aslamazov–Larkin (AL) model. Four different fluctuating regions were recorded as the temperature decreased. The coherence length along the c-axis at 0 K [Formula: see text], interlayer coupling strength s, Fermi velocity [Formula: see text] of the carriers and Fermi energy [Formula: see text] were calculated for both samples with x = 0.0 wt.% and 1.5 wt.%.

Superconducting Fluctuations above Tc and pair breaking parameters of two dimensional Niobium Nitride Films

Transport properties have been investigated for the epitaxial superconducting NbN thin films. We analysed the excess conductance σ’ ≡ σ(T) - σN by the sum of the Aslamazov-Larkin (AL) and Maki-Thompson (MT) terms for thermal fluctuations above Tc, where the σN ≡1/RsqN is the normal state sheet conductance. We have found that the theoretical expression σ’theo (T) = σ’AL (T) + σ’MT (T,δ) can be well fitted to σ’exp (T) with use of the suitable value of the pair breaking parameter δ in the MT term relating to the inelastic scattering rate 1/τin(T) as δ = πħ/8kBTτin. The rate 1/τin(T) given by the sum of 1/τfluc(T), 1/τe-e(T) and 1/τe-ph (T) is determined from the analysis of the magneto-conductance Δσ = σ(H) – σ(0) by the sum of AL, MT and the localization terms, where the first, second and third terms correspond to the rate due to the superconducting fluctuation effect, electron-electron and electron-phonon interactions, respectively. The RsqN dependence of δ is expressed by δ = δ0 + αRsqN, where the first term δ0 due to 1/τe-ph (T) and the second term due to the sum of 1/τfluc(T) and 1/τe-e(T). Although we obtained a reasonable value of Debye temperature ΘD ≈630 K from the δ0, the magnitude of the α is about 5 times larger than the theoretical value.

Excess Conductivity Investigation of Y3Ba5Cu8O18±δ Superconductors Prepared by Various Parameters of Planetary Ball Milling Technique

Superconducting samples of type Y3Ba5Cu8O18±δ were elaborated by using a planetary high-energy ball milling (HEBM) technique with various parameters. Phases, microstructure, and superconductivity have been examined using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and electrical resistivity measurements. SEM investigation shows the occurrence of nanoentities embedded into the superconducting matrix for samples prepared by a ball milling technique. The main objective of this study is to investigate the influence of ball milling parameters on the fluctuation-induced conductivity (FIC). The electrical resistivity versus temperature, ρ(T), above T c was analyzed using Lawrence–Doniach (LD) and Aslamazov–Larkin (AL) models. Different fluctuation regimes indicated by short-wave fluctuation (SWF) and three-dimensional (3D), two-dimensional (2D), one-dimensional (1D), and critical region (CR) fluctuations were identified. The coherence length at zero temperature, the effective layer thickness, the critical magnetic fields, and the critical current densities are determined. The superconducting parameters strongly depend on the planetary ball milling technique, and the results are explained in relevancy to the microstructure. It was found that the achievement of a microstructure with well-dispersed nanoentities is an effective way for introducing pinning centers for enhancing critical current density and flux pinning capability of bulk Y-358.