high-Tc Phase Research Articles

Collapse of metallicity and high-Tc superconductivity in the high-pressure phase of FeSe0.89S0.11

We investigate the high-pressure phase of the iron-based superconductor FeSe0.89S0.11 using transport and tunnel diode oscillator studies using diamond anvil cells. We construct detailed pressure-temperature phase diagrams that indicate that the superconducting critical temperature is strongly enhanced by more than a factor of four towards 40 K above 4 GPa. The resistivity data reveal signatures of a fan-like structure of non-Fermi liquid behaviour which could indicate the existence of a putative quantum critical point buried underneath the superconducting dome around 4.3 GPa. With further increasing the pressure, the zero-field electrical resistivity develops a non-metallic temperature dependence and the superconducting transition broadens significantly. Eventually, the system fails to reach a fully zero-resistance state, and the finite resistance at low temperatures becomes strongly current-dependent. Our results suggest that the high-pressure, high-Tc phase of iron chalcogenides is very fragile and sensitive to uniaxial effects of the pressure medium, cell design and sample thickness. This high-pressure region could be understood assuming a real-space phase separation caused by nearly concomitant electronic and structural instabilities.

Unveiling the quasiparticle behaviour in the pressure-induced high-Tc phase of an iron-chalcogenide superconductor

Superconductivity of iron chalocogenides is strongly enhanced under applied pressure yet its underlying pairing mechanism remains elusive. Here, we present a quantum oscillations study up to 45 T in the high-Tc phase of tetragonal FeSe0.82S0.18 up to 22 kbar. Under applied pressure, the quasi-two-dimensional multi-band Fermi surface expands and the effective masses remain large, whereas the superconductivity displays a threefold enhancement. Comparing with chemical pressure tuning of FeSe1−xSx, the Fermi surface expands in a similar manner but the effective masses and Tc are suppressed. These differences may be attributed to the changes in the density of states influenced by the chalcogen height, which could promote stronger spin fluctuations pairing under pressure. Furthermore, our study also reveals unusual scattering and broadening of superconducting transitions in the high-pressure phase, indicating the presence of a complex pairing mechanism.

Microstructure and Superconducting Properties of Bi-2223 Synthesized via Co-Precipitation Method: Effects of Graphene Nanoparticle Addition.

The effects of graphene addition on the phase formation and superconducting properties of (Bi1.6Pb0.4)Sr2Ca2Cu3O10 (Bi-2223) ceramics synthesized using the co-precipitation method were systematically investigated. Series samples of Bi-2223 were added with different weight percentages (x = 0.0, 0.3, 0.5 and 1.0 wt.%) of graphene nanoparticles. The samples' phase formations and crystal structures were characterized via X-ray diffraction (XRD), while the superconducting critical temperatures, Tc, were investigated using alternating current susceptibility (ACS). The XRD showed that a high-Tc phase, Bi-2223, and a small low-Tc phase, Bi-2212, dominated the samples. The volume fraction of the Bi-2223 phase increased for the sample with x = 0.3 wt.% and 0.5 wt.% of graphene and slightly reduced at x = 1.0 wt.%. The ACS showed that the onset critical temperature, Tc-onset, phase lock-in temperature, Tcj, and coupling peak temperature, TP, decreased when graphene was added to the samples. The susceptibility-temperature (χ'-T) and (χ″-T) curves of each sample, where χ' and χ″ are the real and imaginary parts of the susceptibility, respectively, were obtained. The critical temperature of the pure sample was also measured.

Study of the Structural and Electrical Properties of Bi2-xAgxBa2-ySryCa2Cu3O10+δ System

This study included preparing samples of the compound (Bi2Ba2Ca2Cu3O10+δ) by the solid state reaction method under a hydrostatic pressure 8 ton/cm2 and annealing temperature 840oC. X-ray diffraction (XRD), scanning electron microscopy (SEM), dc electrical resistivity measurements by four point probe method were used to investigate the microstructural and superconducting properties of Bi¬2223 samples. The X-rays diffraction study for the compound (Bi2Ba2Ca2Cu3O10+δ ) showed that it has Tetragonal type of crystal structure. The partial replacement of the component Ag in Bi, and Sr component in Ba simultaneously, the compound becomes (Bi2-xAgxBa2-ySryCa2Cu3O10+δ) with (x ,y) values equal to (x= 0.2, y= 0.1, 0.2, 0.3,0.4). The study of the crystal structure test showed that the structure retains on the tetragonal type with a high Tc phases (2223), low Tc phase(2212) and impurity phases, and the critical temperature Tc steps-up from (125K) to (137K) at substitution rate (x= 0.2, y= 0.1). But at increasing the substitution rate for (y) and the stability of (x) rate more than (x= 0.2, y= 0.1), the temperature declines to (108 K). Finally, the microstructural of the samples has been studies and tested by Scanning Electron Microscope for knowing the components' rates in the compound; how the compound partial substitution affect in the components; and specifying the quantitative and qualitative rates of the components in the compound.

Layer-Number-Independent Two-Dimensional Ferromagnetism in Cr3Te4

In a conventional magnetic material, a long-range magnetic order develops in three dimensions, and reducing a layer number weakens its magnetism. Here we demonstrate anomalous layer-number-independent ferromagnetism down to the two-dimensional (2D) limit in a metastable phase of Cr3Te4. We fabricated Cr3Te4 thin films by molecular-beam epitaxy and found that Cr3Te4 could host two distinct ferromagnetic phases characterized with different Curie temperatures (TC). One is the bulk-like "high-TC phase" showing room-temperature ferromagnetism, which is consistent with previous studies. The other is the metastable "low-TC phase" with TC ≈ 160 K, which exhibits a layer-number-independent TC down to the 2D limit in marked contrast with the conventional high-TC phase, demonstrating a purely 2D nature of its ferromagnetism. Such significant differences between two distinct phases could be attributed to a small variation in the doping level, making this material attractive for future ultracompact spintronics applications with potential gate-tunable room-temperature 2D ferromagnetism.

Impact of Ca(BO2)2 Doping on High-Tc Phase Formation and Transport Properties of Bi(Pb)-2223 Superconductor

Proper Doping of a high-temperature superconductor (HTS) Bi(Pb)-2223 is an effective route to prepare Bi(Pb)-2223 HTS with enhanced transport characteristics. In this paper, we studied the impact of Ca(BO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> doping on high-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> phase formation kinetics and transport critical current density of Bi(Pb)-2223. Samples with a nominal composition of Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.7</sub> Pb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Ca <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-x</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> [Ca(BO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> , x = 0 −0.15 were prepared by the solid-state reaction method. The phase evolution of the prepared materials was studied by X-ray diffraction analysis (XRD). The resistivity and critical current density were measured by the standard four-probe method. Scanning electron microscopy (SEM) combined with Energy Dispersive X-ray (EDX) microanalysis (SEM-EDX) was used to examine the microstructure and elemental composition of samples. The obtained results show that Ca(BO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> doping leads to the promotion of the high-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> phase formation and enhancement of the transport critical current density ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_c)</i> in Bi(Pb)-2223 HTS.

Electrical Transport Measurements on Layered La(O,F)BiS2 under Extremely High Pressure

Layered La(O,F)BiS2 exhibits drastic enhancements of the superconducting transition temperature (Tc) under high pressure among the BiS2-based superconducting family. However, the high-pressure application beyond a high-Tc phase of the monoclinic structure has not been conducted. In this study, the electrical transport properties in La(O,F)BiS2 single crystal are measured under high pressures up to 83 GPa. An insulating phase without superconductivity is observed under a higher-pressure region above 16 GPa. Moreover, the sample exhibits metallicity and superconductivity above 60 GPa. The newly observed hidden semiconducting phase and reentrant superconductivity have attracted much attention in BiS2-based compounds.

Superconductivity of BSCCO Compound Substituted Partially by Zr Nanoparticles at Bi Site

High-temperature superconductors with a nominal composition Bi2- xZrxPb0.4Sr2Ca2Cu3Oy for (0≤x≤0.3) were prepared by solid-state reaction method. Effects of the Zr nanoparticles substitution at Bi sites have been studied to obtain the optimum concentration for the formation and stabilization of the superconducting samples. Electrical resistivity measurements of the samples showed that the higher critical temperature TC was found at 118 K, which is for the composition Bi1.95Zr0.05Pb0.4Sr2Ca2Cu3Oy. Semiconductor behavior noticed for samples with concentration higher than 0.2. The X-ray diffraction results for all superconducting samples showed an orthorhombic structure with two phases, 2223 high-TC phase and 2212 low-TC phase. The scanning electron microscope has been used to identify the morphology of the superconducting phase. The plate-like grains of the high Bi-2223 phase appeared in most samples besides changes in morphology of the samples with increasing dopant concentration

Fragile Pressure-Induced Magnetism in FeSe Superconductors with a Thickness Reduction.

The emergence of high transition temperature (Tc) superconductivity in bulk FeSe under pressure is associated with the tuning of nematicity and magnetism. However, sorting out the relative contributions from magnetic and nematic fluctuations to the enhancement of Tc remains challenging. Here, we design and conduct a series of high-pressure experiments on FeSe thin flakes. We find that as the thickness decreases the nematic phase boundary on temperature-pressure phase diagrams remains robust while the magnetic order is significantly weakened. A local maximum of Tc is observed outside the nematic phase region, not far from the extrapolated nematic end point in all samples. However, the maximum Tc value is reduced associated with the weakening of magnetism. No high-Tc phase is observed in the thinnest sample. Our results strongly suggest that nematic fluctuations alone can only have a limited effect while magnetic fluctuations are pivotal on the enhancement of Tc in FeSe.

Superconductivity Measurements of (Hg,Tl)-1223 Compound Prepared in Capsule

In this paper, investigations were carried out on the effects of simultaneous partial substitution of Tl at the Hg site on the physical properties of an Hg1-xTlxBa2Ca2Cu3O8+δ cuprate superconductor with x= 0, 0.1, 0.2, 0.3 and 0.4. Two steps of the solid state reaction method were used to prepare samples in capsule. The results showed that the optimum sintering temperature was equal to 850 ᵒC and the sintering time was equal to 20 h for the prepared samples. &#x0D; The best conditions for constitution and stabilization of the high Tc phase-1223 were obtained by investigating the effects of Tl substitution on Hg site and oxygen content (δ) on the superconducting properties.&#x0D; Structural investigation revealed that all the samples have a tetragonal structure with two phases, namely an Hg-1223 high Tc phase as a main phase and an Hg-1212 low Tc phase. Besides, some impurity phases like CuO and CaHgO2 were found. The increase of Tl content in Hg1-xTlxBa2Ca2Cu3O8+δ compound from 0 to 0.4 caused a change in the lattice parameter, density of the unit cell (ρm), and c/a values.&#x0D; HgBa2Ca2Cu3O8+δ compound exhibited a critical transition temperature that is equal to 115 K. On the other side, the results showed that the highest Tc was 119 K for Hg0.8Tl0.2 Ba2Ca2Cu3O8+δ. The oxygen content (δ= 0.46) was expected to be the optimum hole doping for Hg0.8Tl0.2 Ba2Ca2Cu3O8+δ compound, which means in our opinion that δ plays a remarkable role in the assessment of Tc.

A Photoluminescent Lead Bromide Hybrid Perovskite Molecular Ferroelastic Semiconductor with Sequential High-Tc Phase Transitions.

Organic-inorganic hybrid lead halide perovskites have attracted great interest for their use in promising optoelectronic applications. However, reports of photoluminescent perovskite molecular ferroelastic semiconductors with sequential high-Tc phase transitions have been scarce. In this work, a one-dimensional lead bromide hybrid perovskite [N,N-dimethylethanolammonium]PbBr3 has been synthesized, undergoing high-Tc sequential phase transitions at around 351 and 444 K, higher than those of most previously discovered hybrid perovskite phase transition materials. The specific intermolecular hydrogen bond between cationic molecules provides the greatest contribution to its high Tc by increasing the barrier of molecular motion under the temperature stimuli. The prominent ferroelastic domain evolution is visually observed under orthogonally polarized light. In addition, [N,N-dimethylethanolammonium]PbBr3 exhibits semiconducting and orange light emission characteristics. This finding opens up an avenue for designing high-performance ferroelastic materials and provides great motivation for discovering new multifunctional materials for the next generation of smart devices.

Structural and transition tempreature of HgPb

solid state reaction technique (SSR) was used to prepare high-Tc phase in superconductors the effect of additional Pb to was investigated it has been found

Effect of Adding Ag Nanoparticles onto Magnetic and Structural Properties of BSCCO Superconducting Compound

Effect of adding silver nanoparticles on Bi1.7Pb0.3Sr2Ca2Cu3O10+δ superconductor phase by solid state reaction technique. It was studied the significant variations in the superconducting, magnetic and structural properties of Bi-2223 phase. Ag NPs concentration of tiny particles varied, (0 - 1,25) % from the total weight mass of the BPSCCO compound were characterized by X-ray diffraction (XRD) and EDX spectrum measurements. It was found that adding Ag nanoparticles to BSCCO was enhanced the (Bi, Pb)-2223 phase formation up to x=1.25 wt%. On the other hand, the low concentrations of Ag nanoparticles of 0.25 wt% retarded the high-Tc phase formation and (Tc) measured that had the maximum improvement in Tc for most samples. The surface morphology investigated were examined by SEM, which the grain size increased with an increase Ag NPs, while the grain size examination showed that both the size and number of voids were reduced. Magnetization variance was measured of the samples by M - T curve, where the highest value for x = 1.25 wt%, and it become clear when the magnetic and resistance transition points are close to each other. Moreover, Critical current density (Jc ) characteristic curves were measured at temperature range (2-150) K.

Evaluation of crystallographic and electrical-superconducting features of Bi-2223 advanced ceramics with vanadium addition

In the current study, the effect of vanadium particles on the electrical, superconducting, crystallographic, key structural and morphological features of Bi1.8Sr2.0Ca2.2Cu3.0VxOy superconducting materials is examined with the aid of powder X-ray diffraction (XRD), scanning electron microscope (SEM), electron-dispersive X-ray (EDX) and dc electrical resistivity over the temperature (ρ-T). The vanadium-added Bi1.8Sr2.0Ca2.2Cu3.0VxOy (Bi-2223) superconducting materials are prepared within the molar ratios between x = 0.00 and 0.30 using the conventional solid-state reaction technique. The temperature-dependent electrical resistivity measurements show that the existence of vanadium atom in the superconducting system damages seriously the Bi-2223 (high-Tc) phase content in the crystal structure as a result of the formations/disappearances of new impurity phases. On this basis, the amplitude Ψ0 of wave function founded on the super-electrons is considerably reduced with the vanadium addition. The critical onset and offset transition temperature values truncate from the values of 110.92 K and 97.45 K to 103.17 K and 18.38 K in case of the maximum vanadium addition level of x = 0.30. Similarly, the XRD results present that the average crystallite size and c-axis length parameters are noted to decrease considerably whereas a-axis length, strain and relativistic dislocation density ratios are calculated to enlarge harshly depending on the addition content level. It is also obtained that the vanadium inclusions lead to increase seriously the permanent crystal structure problems, disorders, misorientations, lattice strains, crack-producing omnipresent flaws and grain boundary coupling problems in the active Cu–O2 consecutively stacked layers in the superconducting core, being assured by SEM analyses. Besides, the SEM results show that the enhancement of vanadium addition level in the crystal structure damages remarkably the flaky layers of platelet-like shape for the grains. In fact, the excess vanadium addition seriously damages the general characteristic view (flaky layer structure) of Bi-2223 compound. Based on the EDX findings, the main reason for the degradation of fundamental characteristic properties of Bi-2223 system may stem from the possible replacement of aliovalent vanadium impurities for the copper-sites in the crystal structure. Namely, the vanadium addition in the crystal structure is ploughed to improve the fundamental crystallographic and electrical-superconducting features of bulk Bi-2223 superconducting materials.

Competing hydrogen-bonding interactions in a high-Tc organic molecular-ionic crystal with evident nonlinear optical response

An organic molecular-ionic crystal of (TPPO–H)2SO4 exhibits moderate NLO response which is twice that of KDP and competing hydrogen-bonding interactions triggered high-Tc phase transition.

Monofluorine substitution achieved high-Tcdielectric transition in a one-dimensional lead bromide hybrid photoluminescent perovskite semiconductor

H/F substitution applied on (TEA)PbBr3gives monofluoride (FTEA)PbBr3, showing evidentTcenhancement, dielectric switching, semiconductor, and photoluminescence properties.

Influence of Dysprosium Addition on the Phase Formation and Transport Properties of Hg-1223 Superconductor

We study the influence of dysprosium (III) oxides on the superconductivity properties of Hg-1223 material. Dysprosium-free Hg-1223 and dysprosium-doped HgBa2Ca2Cu3DyxO8+δ (x = 0.00–0.075 wt%) superconductors are synthesized by sealed quartz tube technique. Our results demonstrate that a presence of dysprosium oxide not only makes the Ba2Ca2Cu3Oy multiphase precursor more reactive and enhances the kinetics of the reaction, but also leads to the promotion of the high-Tc phase and enhancement of the transport critical current densities Jc.

Structure and superconducting properties of multiple phases of (NH3)yAExFeSe (AE: Ca, Sr and Ba)

We synthesized the alkaline-earth metal-doped FeSe compounds (NH3)yAExFeSe (AE: Ca, Sr and Ba), using the liquid NH3 technique, to determine their superconducting properties and crystal structures. Multiple superconducting phases were obtained in each sample of (NH3)yCaxFeSe and (NH3)yBaxFeSe, which showed two superconducting transition temperatures (Tc’s) as high as 37–39 K and 47–48 K at ambient pressure, hereinafter referred to as the ‘low-Tc phase’ and ‘high-Tc phase’, respectively. The high-Tc phases in (NH3)yCaxFeSe and (NH3)yBaxFeSe were metastable, and rapidly converted to their low-Tc phases. However, Tc values of 38.4 K and 35.6 K were recorded for (NH3)ySrxFeSe, which displayed different behavior than (NH3)yCaxFeSe and (NH3)yBaxFeSe. The Le Bail fitting of x-ray diffraction (XRD) patterns provided lattice constants of c = 16.899(1) Å and c = 16.8630(8) Å for the low-Tc phases of (NH3)yCaxFeSe and (NH3)yBaxFeSe, respectively. The lattice constants of their high-Tc phases could not be determined due to the disappearance of the high Tc phase within a few days. The XRD pattern for (NH3)ySrxFeSe indicated the coexistence of two phases with c = 16.899(3) Å and c = 15.895(4) Å. The former value of c in (NH3)ySrxFeSe is almost the same as those of the low-Tc phases in (NH3)yCaxFeSe and (NH3)yBaxFeSe. Therefore, the phase with c = 16.899(3) Å in (NH3)ySrxFeSe must correspond to the superconducting phase with the Tc of 38.4 K, while the superconducting phase with Tc = 35.6 K is assigned to the crystal phase with c = 15.895(4) Å. For (NH3)ySrxFeSe, a high-Tc phase with Tc = 47–48 K has not yet been obtained, but a new phase showing the Tc value of 35.6 K was clearly obtained. This is the first systematic study of the preparation, crystal structure, and superconductivity of alkaline-earth metal-doped FeSe, (NH3)yAExFeSe.

A Detailed Numerical Analysis for High-Tc Superconductivity and Physical Analysis of the High-Tc Phase Diagram Based on the U(1) Slave-Boson Approach to the t − J Hamiltonian

One of the major theoretical challenges in high-Tc superconductivity is to first reproduce the observed phase diagrams that display the monotonously decreasing pseudogap temperature T* and the dome-shaped superconducting phase transition temperature Tc in the plane of temperature vs. hole concentration. Earlier Lee and Salk [J. Korean Phys. Soc. 37, 545 (2000); Phys. Rev. B 64, 052501 (2001)] reported a successful reproduction of the phase diagram by providing a realistic gauge theoretic [SU(2)/U(1)] slave-boson approach to the t - J Hamiltonian. Most recently, we [S.-H. S. Salk, Quantum Studies: Mathematics and Foundations 5, 149 (2018)] presented a comprehensive discussion on both the SU(2) and the U(1) approaches from which one can readily understand the intimate relationship between the two formalisms and discussed that both approaches can lead to room-temperature superconductivity with suitably high values of the antiferromagnetic coupling constant J, owing to the demonstration of identical physical propensities, i.e., the higher the J is, the higher the superconducting phase transition temperature Tc is. Here, we discuss hither-to-unreported detailed numerical computations of the phase diagrams by varying the values of J by using the U(1) gauge slave-boson approach to the t − J Hamiltonian. For the sake of testing convergence, we vary the unit-cell lattice sizes from 10 × 10 to a sufficiently large size of 50 × 50. We find that even a small square lattice size of 20 × 20 is seen to show reliable agreement with the results for higher lattice sizes while the 50 × 50 lattice size displays complete convergence in both T*and Tc. In addition, we present a physical analysis of the structure of the high-Tc phase diagram, focusing on the role of the spin pairing order in association with the interplay between the pseudo-gap (spin gap) temperature and the bose-condensation temperature/dome-shaped superconducting phase transition temperature.

The Effect of Tungsten Nanoparticles on Superconducting of The Compound Bi2-xPb0.3WXSr2Ca2Cu3O10+δ

By using a conventional solid-state reaction technique, a group of the superconducting samples with nominal composition Bi2-xPb0.3WxSr2Ca2Cu3O10±δ with (0≤x≤0.5) sintered at 840ᵒC for 140h in the air have been prepared. The effect substitution of tungsten nanoparticles on the physical properties of Bi sites was studied. X-ray diffraction (XRD) studies showed that all our samples are polycrystalline with orthorhombic structures and presence two phases: high-Tc phase (2223), low-Tc phase (2212) and an impurity phase Some impurities likeSr2Ca2Cu7Oδ, CaO and WO . In the prepared samples the lattice parameter values and the volume fraction of high-Tc phase are calculated. Electrical resistivity measurements show that the values of critical temperature Tc increase with tungsten content. The highest transition temperature, Tc, obtained for Bi2-xPb0.3WXSr2Ca2Cu3O10+δ composition was 191.8K with x=0.3.