Superconducting Volume Fraction Research Articles

AC Magnetic Susceptibility: Mathematical Modeling and Experimental Realization on Poly-Crystalline and Single-Crystalline High-Tc Superconductors YBa2Cu3O7-δ and Bi2-xPbxSr2Ca2Cu3O10+y.

The multifaceted inductive technique of AC magnetic susceptibility (ACMS) provides versatile and reliable means for the investigation of the respective properties of magnetic and superconducting materials. Here, we explore, both mathematically and experimentally, the ACMS set-up, based on four coaxial pick-up coils assembled in the second-derivative configuration, when employed in the investigation of differently shaped superconducting specimens of poly-crystalline YBa2Cu3O7-δ and Bi2-xPbxSr2Ca2Cu3O10+y and single-crystalline YBa2Cu3O7-δ. Through the mathematical modeling of both the ACMS set-up and of linearly responding superconducting specimens, we obtain a closed-form relation for the DC voltage output signal. The latter is translated directly to the so-called extrinsic ACMS of the studied specimen. By taking into account the specific characteristics of the studied high-Tc specimens (such as the shape and dimensions for the demagnetizing effect, porosity for the estimation of the superconducting volume fraction, etc.), we eventually draw the truly intrinsic ACMS of the parent material. Importantly, this is carried out without the need for any calibration specimen. The comparison of the mathematical modeling with the experimental data of the aforementioned superconducting specimens evidences fair agreement.

Rapid optical switching of latched electrical resistance in a high-T c superconducting tape

We report microsecond timescale switching between the superconducting and normal states of commercially manufactured high-Tc superconducting wires using optical radiation to heat the conductor above Tc. The achieved voltages and switching times have significant implications for a new class of thermal switches. The report contains experimental data for photo-induced microsecond scale voltage transients as well as numerical analysis of heat propagation through the material in response to optical radiation. The microbridges are etched into commercially manufactured coated conductors and submerged in liquid nitrogen. By varying the magnitude of the transport current, two different optical responses are identified. At low transport currents, short-lived voltage transients occur, transitioning to persistent latching once the current is increased above a threshold value. The microbridge, therefore, behaves as a fast opening and closing switch when carrying low currents or an optically latched thyristor at high currents. This is understood to occur due to critical current suppression as a result of heating from the optical pulse. Optically induced heating reduces the superconducting volume fraction, and Joule heating due to the transport current interaction with the high temperature superconducting occurs, which either causes short-lived or stable self-heating normal regions dependent on the magnitude of the transport current. This study is concluded with an estimate of the energy necessary to drive the microbridge into the resistive state. The observed behavior can potentially be utilized as a switching element in superconducting transformer rectifiers where high frequency switch operation is required.

Ferromagnetic exchange field stabilized antiferromagnetic ordering in a cuprate superconductor

We report experimental evidence of formation of antiferromagnetic clusters in composites made of a cuprate superconductor La1.85Sr0.15CuO4 (LCu) and a ferromagnet La0.6Sr0.4CoO3 (LCo). From linear and non-linear ac-susceptibility measurement on this composite material it is found that the exchange field of LCo suppress the dynamic antiferromagnetic spin fluctuation of LCu and convert it into the short range ordered superparamagnetic type antiferromagnetic (AFM) clusters at the cost of superconducting volume fraction. These shrank superconducting volume fraction shows quantum size effect (QSE) and follows DeGennes-Tinkham theory on finite size effect of superconductor.

Synthesis of lithium- and pyridine-intercalated superconductors Li x (C5H5N) y SnSe2

Superconductors Li x (C5H5N) y SnSe2 (x = 0.3–1.0) have been successfully synthesized by the intercalation of pyridine molecules together with Li+ ions into an insulator SnSe2 with the layered structure. The co-intercalation has been carried out by immersing powdery SnSe2 and Li metal in the organic solvent pyridine at 70 °C. The spacing between the adjacent Sn layers is expanded from ∼6 to ∼12 Å through the co-intercalation. It has been found that the superconducting transition temperature T c ∼ 7.5–7.9 K is almost independent of Li-content x(Li) and the superconducting volume fraction has a maximum at x(Li) = 0.5.

Structural properties of BaPb1-xBixO3 nanostructures

Electrical resistance as a function of temperature, R(T), and X-ray powder diffractometry (XRD) patterns are reported for polycrystalline samples of the BaPb1-xBixO3 system. R(T) measurements conducted with single phase samples show metal-like behavior for BaPbO3, superconductivity in the 0.005 < x < 0.30 range, and a insulating regime for x > 0.30. A careful analysis of the onset of the critical temperature (TC) revels dependence on sample composition for 0.005 < x < 0.30. We argue that the composition-dependence of TC is related to the superconducting volume fraction which ultimately leads to connected or disconnected superconducting clusters, similar to granular superconductors.

The interplay between the incommensurate spin correlations and superconductivity in Mn substituted La1.90Sr0.10CuO4

The Mn substitution effect on superconductivity and spin correlations in La1.90Sr0.10Cu1−y Mn y O4 was investigated by means of magnetic susceptibility and neutron scattering measurements. The superconducting (SC) transition temperature (T c) and the SC volume fraction are reduced by Mn substitution with y = 0.01. It was clarified that the peak-splitting of the incommensurate (IC) low-energy spin excitations narrows by 30% and the magnetic ordering temperature is significantly enhanced in the y = 0.01 sample. Thus, the SC state and the magnetic ordering state coexist at low temperature. Furthermore, incommensurability (δ), corresponding to half the distance between the IC peaks, and T c (∼ 18 K) of y = 0.01, both follow the linear T c−δ relation established for the pristine La2−x Sr x CuO4 (LSCO). Therefore, although Tc varies as a result of Mn substitution, spin correlations are closely coupled to superconductivity as is the case for LSCO.

Protonation enhanced superconductivity in PdTe2

Electrochemical ionic liquid gating is an effective way to intercalate ions into layered materials and modulate the properties. Here we report an enhanced superconductivity in a topological superconductor candidate PdTe2 through electrochemical gating procedure. The superconducting transition temperature was increased to approximately 3.2 K by ionic gating induced protonation at room temperature. Moreover, a further enhanced superconductivity of both superconducting transition temperature and superconducting volume fraction was observed after the gated samples were placed in a glove box for 2 months. This may be caused by the diffusion of protons in the gated single crystals, which is rarely reported in electrochemical ionic liquid gating experiments. Our results further the superconducting study of PdTe2 and may reveal a common phenomenon in the electrochemical gating procedure.

Temporal Spinodal Decomposition of the Fe1+yTe1−xSex Crystals and its Impact on Superconducting Properties

Precipitated phases, formed by spinodal decomposition during long‐term storage in a desiccator in dry atmosphere, are found with the X‐ray diffraction (XRD) study of Fe1+y Te1−x Se x crystals. Their compositions are deduced from the position of satellite Bragg reflections in the XRD pattern. In particular, in the Fe1.19Te0.58Se0.42 crystal, traces of phases with significantly higher tellurium content, namely Fe1+y Te0.9Se0.1 and FeTe, are found. The detection and analysis of side bands in the diffraction pattern of an aged crystal indicate spinodal decay. It leads to the formation of a modulated structure in the entire volume of the sample and to strain in the crystal structure. In turn, this results in a significant improvement in the superconducting characteristics. Specifically, the resistive transition narrows to 2 K at the onset temperature 14.5 K, and the superconducting volume fraction increases up to about 100%.

Comparative Study of the Effects of La-Substituted Ca in (Bi, Pb):2212 and (Bi, Pb):2223 Superconductors

We report here a comparative study of the effects of La-substituted Ca on (Bi, Pb):2212 and (Bi, Pb):2223 superconductors with various La content (0.00 ≤ x ≤ 0.30). Regardless of the effects of La, it is evident that the superconducting volume fraction, excess of oxygen, critical concentration for quenching superconductivity, Vickers hardness, anisotropy, interlayer coupling, critical magnetic fields, and critical current were higher for the 2212 series than the 2223 series. In contrast, orthorhombic distortion, c-parameter, crystallite diameter, doping distance, distance between two Cu atoms, hole carrier/Cu ion ratio, melting temperature Tm, critical temperature Tc, onset of diamagnetic TcM, surface energy, elastic component, resistance pressure, and c-axis coherence length were higher for the 2223 series than the 2212 series. An inverse linear relationship between Tm and Tc was estimated for both series, and for room-temperature (RT) bismuth–strontium–calcium–copper–oxide (BSCCO) superconductors, the required Tm values should be 1048.03°C for the 2223 series and 784.48°C for the 2212 series. Surprisingly, the difference in temperature between zero resistivity and diamagnetic onset |TcM − TcR| for La = 0.30 samples is 30 K. In the critical field region (CFR), the exponents of order parameters (OPD) are two-dimensional (2D), but their values were higher for the 2212 series than the 2223 series. Further, they became three-dimensional (3D) as La increased to 0.30 due to the reduced effective length in highly substituted samples. Our results were discussed with the help of the differences in the physical parameters between the considered series. These findings revealed that the 2212 series is more suitable for applications that need higher hardness and critical fields and currents. In contrast, the 2223 series is more suitable for research for higher Tc and altering plastic deformation. To our knowledge, the present systematic investigation has not been reported elsewhere, which highlights the present work.

Anomalous charge density wave state evolution and dome-like superconductivity in CuIr2Te4−x Se x chalcogenides

We report the anomalous charge density wave (CDW) state evolution and dome-like superconductivity in CuIr2Te4−x Se x (0 ⩽ x ⩽ 0.5) series. Room temperature powder x-ray diffraction (XRD) results indicate that CuIr2Te4−x Se x (0 ⩽ x ⩽ 0.5) compounds retain the same structure as the host CuIr2Te4 and the unit cell constants a and c manifest a linear decline with increasing Se content. Magnetization, resistivity and heat capacity results suggest that superconducting transition temperature (T c) exhibits a weak dome-like variation as substituting Te by Se with the maximum T c = 2.83 K for x = 0.1 followed by suppression in T c and simultaneous decrease of the superconducting volume fraction. Unexpectedly, the CDW-like transition (T CDW) is suppressed with lower Se doping (0.025 ⩽ x ⩽ 0.2) but re-emerges at higher doping (0.25 ⩽ x ⩽ 0.5). Meanwhile, the temperature-dependent XRD measurements show that the trigonal structure is stable at 20 K, 100 K and 300 K for the host sample and the doping composition with x = 0.5, thus we propose that the behavior CDW-like transition arises from the disorder effect created by chemical doping and is not related to structural transition. The lower and the upper critical fields of these compounds are also addressed.

Double Superconducting Dome and Triple Enhancement of T_{c} in the Kagome Superconductor CsV_{3}Sb_{5} under High Pressure.

CsV_{3}Sb_{5} is a newly discovered Z_{2} topological kagome metal showing the coexistence of a charge-density-wave (CDW)-like order at T^{*}=94 K and superconductivity (SC) at T_{c}=2.5 K at ambient pressure. Here, we study the interplay between CDW and SC in CsV_{3}Sb_{5} via measurements of resistivity, dc and ac magnetic susceptibility under various pressures up to 6.6GPa. We find that the CDW transition decreases with pressure and experience a subtle modification at P_{c1}≈0.6-0.9 GPa before it vanishes completely at P_{c2}≈2 GPa. Correspondingly, T_{c}(P) displays an unusual M-shaped double dome with two maxima around P_{c1} and P_{c2}, respectively, leading to a tripled enhancement of T_{c} to about 8K at 2GPa. The obtained temperature-pressure phase diagram resembles those of unconventional superconductors, illustrating an intimated competition between CDW-like order and SC. The competition is found to be particularly strong for the intermediate pressure range P_{c1}≤P≤P_{c2} as evidenced by the broad superconducting transition and reduced superconducting volume fraction. The modification of CDW order around P_{c1} has been discussed based on the band structure calculations. This work not only demonstrates the potential to raise T_{c} of the V-based kagome superconductors, but also offers more insights into the rich physics related to the electron correlations in this novel family of topological kagome metals.

Fermi Surface Geometry and Inhomogeneous Electronic States in Pr1.3−xLa0.7CexCuO4 (x = 0.05) with Small Superconducting Volume Fraction

We have investigated the electronic structure of protect annealed Pr1.3−xLa0.7CexCuO4 (x = 0.05) with small superconducting volume fraction by means of angle-resolved photoemission spectroscopy (AR...

Revisiting the phase diagram of LaFe1−xCoxAsO in single crystals by thermodynamic methods

In this work we revisit the phase diagram of Co-doped LaFeAsO using single crystals and thermodynamic methods. From magnetic susceptibility studies we track the doping evolution of the antiferromagnetic phase, revealing a continuous suppression of $T_\mathrm{N}$ up to 5$\%$ Co doping. In order to study the evolution of the so-called nematic phase, the temperature dependence of the lengths changes along the $a$ and $b$ orthorhombic directions, $\Delta L/L_0$, was determined by high-resolution capacitance dilatometry. The results clearly show a gradual reduction of the orthorhombic distortion $\delta$ and of $T_\mathrm{S}$ with increasing Co content up to 4.5$\%$, while it is completely suppressed for 7.5$\%$ Co. Bulk superconductivity was found in a small doping region around 6$\%$ Co content, while both $T_\mathrm{c}$ and the superconducting volume fraction rapidly drop in the neighbouring doping regime. Ultimately, no microscopic coexistence between the superconducting and magnetic phases can be assessed within our resolution limit, in sharp contrast with other iron-pnictide families, e.g., electron- and hole-doped BaFe$_2$As$_2$.

Study of Carrier Transfer Mechanism When Substituting Strontium at Barium Sites in CuTl-1223 Superconducting Phase

Strontium-doped CuTl-1223 phase has been obtained by employing a nonstoichiometric composition of the form Tl1/2Cu1/2(Ba1−xSrx)Ca1Cu4Oy (x = 0, 0.1, 0.2, 0.3). The superconducting properties of the samples were investigated by x-ray diffraction analysis and four-probe resistivity, alternating-current (AC) susceptibility, and Fourier-transform infrared (FTIR) absorption measurements. The effect of doping strontium atoms on the intrinsic superconductor parameters of these samples was studied by excess conductivity analysis. All the samples showed orthorhombic crystal structure in space group Pmmm, and the cell parameters were determined by using all the planar reflections. The c-axis length and the unit cell volume decreased with Sr doping in the final compound. Suppression of the room-temperature resistivity followed by metallic variations in resistivity versus temperature measurements are typical features for these samples. The zero-resistivity critical temperature and the onset of diamagnetism were suppressed with increasing Sr doping in the final compound. The apical oxygen phonon mode of type Cu(1)–OA–Cu(2) observed at around 548 cm−1 hardened with increasing Sr doping. The excess conductivity analysis revealed that the coherence length along the c-axis, the interlayer coupling, and the Fermi velocity of the carriers increased for the Sr doping levels of x = 0.1 and 0.2 but decreased for the sample with x = 0.3. The values of Bc0(T), Bc1(T), and Jc0(0) increased with increasing Sr doping in the final compound. It is proposed that this effect arises due to an increase in the superconducting volume fraction. A decrease in the value of the London penetration depth λp.d. and the Ginzburg–Landau (GL) parameter shows that the flux-pinning characteristics of the samples were improved by Sr doping. An increase in the mean free time of the carriers and a decrease in the energy required to break apart Cooper pairs result from a decrease in the remanent field scattering induced by the increased population of pinning centers in Sr-doped samples.

Enhanced superconducting properties of double-chain based superconductor Pr[formula omitted]Ba[formula omitted]Cu[formula omitted]O[formula omitted] synthesized by citrate pyrolysis technique

We report the enhanced superconducting properties of double-chain based superconductor Pr2Ba4Cu7O15−δ synthesized by the citrate pyrolysis technique. The reduction heat treatment in vacuum results in the appearance of superconducting state with Tc=22-24 K, accompanied by the higher residual resistivity ratios. The superconducting volume fractions are estimated from the ZFC data to be 50∼55%, indicating the bulk superconductivity. We evaluate from the magneto-transport data the temperature dependence of the superconducting critical field, to establish the superconducting phase diagram. The upper critical magnetic field is estimated to be about 35 T at low temperatures from the resistive transition data using the Werthamer-Helfand-Hohenberg formula. The Hall coefficient RH of the 48-h-reduced superconducting sample is determined to be −0.5×10−3cm3/C at 30 K, suggesting higher electron concentration. These findings have a close relationship with homogeneous distributions of the superconducting grains and improved weak links between their superconducting grains in the present synthesis process.

Effects of Non-magnetic Metallic Zinc Nanoparticles on the Dielectric Properties of CuTl-1223 Superconducting Phase

Synthesis of non-magnetic metallic zinc (Zn) nanoparticles (NPs) and (Zn)x/Cu0.5Tl0.5Ba2Ca2Cu3O10−δ (CuTl-1223) nanoparticle-superconductor composites was carried out by chemical sol-gel and solid-state reaction methods, respectively. Different concentrations of Zn NPs from 1.0 to 4.0 wt.% were inserted in CuTl-1223 superconducting matrix to obtain desired (Zn)x/CuTl-1223 nanoparticle-superconductor composites. The structural properties of these NPs and composites were studied by X-ray diffraction (XRD) technique. The unaffected crystal symmetry of the host CuTl-1223 superconducting phase after the inclusion of Zn NPs from XRD patterns suggested that these NPs were settled across the grain boundaries. Transport electrical properties of (Zn)x/CuTl-1223 composites were investigated by resistivity versus temperature (RT) measurements, and zero resistivity critical temperature (Tc) was found to be increased with Zn NPs contents up to x = 3 wt.%. The enhancement in Tc could be due to the non-magnetic metallic Zn 3d10 (S = 0) NPs that facilitated the conduction of charge carriers across the grain boundaries, while Tc was suppressed beyond x = 3 wt.% contents of Zn NPs due to reduced superconducting volume fraction of CuTl-1223 matrix. Using the LCR meter, dielectric parameters, namely real part (ɛ/r), imaginary part (ɛ//r), tangent loss (tanδ), and ac-conductivity (σac), were measured at varying frequencies and temperatures. The values of ɛ/r, ɛ//r and tanδ were found to be maximum at lower frequencies and became constant at high frequencies, while the value of σac was found to be minimum at lower frequencies and was increased with increasing frequency.

Anomalous Charge Density Wave State Evolution and Dome-Like Superconductivity in CuIr <sub>2</sub>Te <sub>4-X</sub>Se <sub>x</sub>

The interplay between superconductivity (SC) and the charge density wave (CDW)-like order in CuIr2Te4 is systematically explored through Se substitution for Te site through the powder X-ray diffraction (PXRD), magnetic susceptibility, resistivity measurements and heat capacity. CuIr2Te4-XSex (0 ≤ x ≤ 0.5) compounds retain the same structure as the host CuIr2Te4. The unit cell parameters a and c decrease linearly with increasing Se content. Tc exhibits a weak dome-like variation as substituting Te by Se with the maximum Tc = 2.83 K for x = 0.1 followed by suppression in Tc and simultaneous decrease of the superconducting volume fraction. Unexpectedly, the CDW-like transition (TCDW) is suppressed with lower Se doping (0.025 ≤ x ≤ 0.2) but re-emerge at higher doping (0.25 ≤ x ≤ 0.5). We propose that it arises from the disorder effect by chemical doping. The lower and the upper critical field and these compounds are also addressed.

Annealing Effects on the Structural, Surface, and Superconducting Properties of FeTe0.55Se0.45 Single Crystals

In this study, we have investigated the annealing effects on FeTe0.55Se0.45 single crystals in S and Te atmospheres. FeTe0.55Se0.45 single crystals were prepared by self-flux method. The as-grown sample shows a rather broad superconducting transition temperature around 6 K and low superconducting volume fraction, which is due to the relatively low proportion of superconducting phase. After being annealed in different vapor atmospheres, their superconducting properties, such as superconducting transition temperature, critical current density Jc, and superconducting volume fraction, could be greatly improved. All experimental results suggest that the bulk superconductivity of FeTe0.55Se0.45 single crystals can be obtained after annealing and thus present another option to remove the excess Fe, which paves the way for further practical application.

Study of transport and elastic properties of YBCO superconductor by inclusion of GnPs

The variation in superconducting and elastic parameters of YBa2Cu3O7-δ (YBCO) superconductor due to addition of Graphene nanoplatelets (GnPs) was examined. All the composite samples (1-x) YBCO + x GnPs (x = 0.1, 0.3, 0.5, 0.7 and 0.9%) were synthesized by conventional solid state reaction route. The structural and morphological characterizations of composite samples were investigated through the X-ray diffraction and FESEM analysis respectively. An improvement of superconducting transition temperature (TC) was observed with an increasing wt.% of GnPs concentration. Similarly, the critical current density (JC) was found to be increased and optimum value is found to be 892.48 A/cm2 for 0.7 wt.% GnPs added to the sample at 77 K. This may be attributed to the enhancement of superconducting volume fraction and reduction of porosity of the material under the addition of GnPs. Furthermore, to investigate the elastic parameters of the samples Vickers microhardness and Ultrasonic pulse-echo technique were utilized.

Evolution of two bulk-superconducting phases in Sr0.5RE0.5FBiS2 (RE: La, Ce, Pr, Nd, Sm) by external hydrostatic pressure effect

Polycrystalline samples of Sr0.5RE0.5FBiS2 (RE: La, Ce, Pr, Nd, and Sm) were synthesized via the solid-state reaction and characterized using synchrotron X-ray diffraction. Although all the Sr0.5RE0.5FBiS2 samples exhibited superconductivity at transition temperatures (Tc) within the range of 2.1–2.7 K under ambient pressure, the estimated superconducting volume fraction was small, which indicates non-bulk nature of superconductivity in those samples under ambient pressure. A dramatic increase in shielding fraction, which indicates the emergence of the bulk superconductivity was achieved by applying external hydrostatic pressures. We found that two phases, low-P phases with Tc = 2.5–2.8 K and high-P phases with Tc = 10.0–10.8 K, were induced by the pressure effect for samples with RE = La, Ce, Pr, and Nd. Pressure-Tc phase diagrams indicated that the critical pressure for the emergence of the high-P phase tends to increase with decreasing ionic radius of the doped RE ions, which was explained by the correlation between external and chemical pressure effects. According to the high-pressure X-ray diffraction measurements of Sr0.5La0.5FBiS2, a structural phase transition from tetragonal to monoclinic also occurred at approximately 1.1 GPa. Bulk superconducting phases in Sr0.5RE0.5FBiS2 induced by the external hydrostatic pressure effect are expected to be useful for understanding the effects of both external and chemical pressures to the emergence of bulk superconductivity and pairing mechanisms in BiCh2-based superconductors.