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We report the first superconducting tape using an iron-based superconductor (Sr,Na)Fe2As2 fabricated by the powder-in-tube (PIT) technique. Polycrystalline (Sr1−x Na x )Fe2As2 (x = 0.55), which we recently succeeded in synthesizing, was used as the starting powder. First, a silver (Ag) tube was groove-rolled into a square wire. The wire was then flat-rolled into tape form, followed by uniaxial cold pressing. The heat-treated tape exhibits a sharp superconducting transition at 34.5 K. Large transport critical current densities (J c) of over 1.0 × 104 A cm−2 are achieved at 20 K under a magnetic field of 2.5 T. J c at 4.2 K, as estimated from magnetic hysteresis curves, is 1.0 × 105 A cm−2 in 2.0 T, which is comparable to the transport J c reported for (AE,K)Fe2As2 (AE = Ba or Sr) tapes. SEM-EDX observations indicate that some Ag and As-rich material is present between (Sr,Na)Fe2As2 grains, even though no Ag was added to the starting powder. This Ag and As-rich material may strengthen grain connectivity and help to improve the transport J c.

We prepared c-axis-controlled V2O3 thin films by RF magnetron sputtering and proved their metal–insulator transition (MIT) in terms of electronic structure. The lattice constant of the c-axis depends on the film thickness and the lattice mismatch of the substrate and V2O3. MIT is observed at a temperature of ∼150 K in the V2O3 thin films with the lattice constants of c = 13.942 and 13.992 A, although the V2O3 thin film with c = 13.915 A exhibits metallic conductivity without MIT. The electron correlation energy, which corresponds to the energy difference between the lower Hubbard band and the upper Hubbard band, increases with increasing lattice constant of the c-axis. Bandwidths also depend on the lattice constant of the c-axis. The intensity of the a1g orbital around the Fermi level decreases with increasing lattice constant of the c-axis. These results suggest that the electron correlation interaction and bandwidths play important roles in the MIT of c-axis-controlled V2O3 thin films.

(Sr1−xNax)Fe2As2 is a family of the so-called '122 system' of Fe-based superconductors. So far, samples with a limited composition range, i.e. polycrystalline samples for 0 ≤ x ≤ 0.42 with a maximum transition temperature (Tc) of 26 K and a single crystal with x = 0.5 and Tc = 35 K, have been synthesized. Here, we report the synthesis of single-phase polycrystalline samples of (Sr1−xNax)Fe2As2 for a wide range of x from 0 to 0.70 using a stainless-steel pipe-and-cap method. The susceptibilities in the normal and superconducting states were measured as a function of x, and an overall superconducting phase diagram was obtained. As x increased, the structural and anti-ferromagnetic phase transition temperature decreased, and superconductivity began to emerge around x = 0.35. Tc exhibited a dome-like composition dependence with a maximum onset Tc of 36.5 K for x = 0.55. The Rietveld refinement of the powder x-ray diffraction pattern at room temperature for x = 0.55 revealed structural parameters such as the lattice parameters a = 3.857(1) A and c = 12.564(1) A, an Fe–As bond length lFe–As = 2.394(1) A, an As–Fe–As bond angle αAs–Fe–As = 107.3(1)°, and an As height from the Fe layer hAs = 1.419(1) A.

Via thin film deposition techniques, the meta-stable in bulk crystal hexagonal phase of tungsten oxide (hex-WO3) is stabilized as a thin film. The hex-WO3 structure is potentially promising for numerous applications and is related to the structure for superconducting compounds found in WO3. Utilizing ionic liquid gating, carriers were electrostatically induced in the films and an insulator-to-metal transition is observed. These results show that ionic liquid gating is a viable technique to alter the electrical transport properties of WO3.

Using the on-set of third-harmonic susceptibility we have measured vortex melting lines of high-pressure synthesized $({\mathrm{Cu}}_{0.6}{\mathrm{C}}_{0.4}){\mathrm{Ba}}_{2}{\mathrm{Ca}}_{3}{\mathrm{Cu}}_{4}{\mathrm{O}}_{y}$ [(Cu,C):1234] and $({\mathrm{Cu}}_{0.5}{\mathrm{C}}_{0.5}){\mathrm{Ba}}_{2}{\mathrm{Ca}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{y}$ [(Cu,C):1223] with preferentially oriented crystallites and having various carrier concentrations. Vortex melting lines of all (Cu,C):1223 samples and of optimum-doped (Cu,C):1234 were very well described by the commonly accepted theory of melting lines within the two-fluid model. Overdoped (Cu,C):1234 proved to have an anomalous melting line, that was phenomenologically explained by the rather special gaps evolution, that is the significant opening of a second superconducting gap due to $\mathrm{Cu}{\mathrm{O}}_{2}$ outer planes at a temperature lower than the critical one, where the first superconducting gap due to inner planes opens. The experimental melting lines of overdoped (Cu,C):1234 were modelled theoretically by assuming an empirical formula for the temperature dependence of anisotropy factor.

We report on superconducting(SC) characteristics for oxygen-reduced Cu-based five-layered high-temperature superconductor (Cu,C)Ba2Ca4Cu5Oy(Cu-1245(OPT)), which includes five-fold outer planes (OP) and four-fold inner planes (IP).As a result of the reduction of the carrier density, the bulk SC for Cu-1245 (OPT) takes place at the nearly optimally-doped OP with Tc= 98 K that is different from previously-reported Cu-1245(OVD) where IP plays a primary role for the onset of SC. It gives an evidence that the carrier density of the optimally-doped layer determines its bulk Tc.Static antiferromagnetic(AFM) order is evidenced at IP's by zero-field Cu-NMR at low temperature, irrespective of the SC transition at OP's below 98K. This AFM state at IP's is characterized by a carrier localization at low temperatures due to disorder effect, whereas the carrier densities in each layer are similar to Hg-1245(OPT) where the AFM metallic state are realized in IP's. This finding reinforces the phase diagram in which the AFM metallic phase exists between AFM insulator and SC states for the case of ideally-flat CuO2 plane without disorder., 4 pages, 5 figures

Single crystals of a new sodium manganese oxide, NaMn2O4, were synthesized for the first time using a high-temperature and high-pressure technique. The NaMn2O4 single crystal is black, has a needle shape, and crystallizes in the orthorhombic calcium ferrite-type structure, space group Pnam with a = 8.9055 ( 18 ) A , b = 11.0825 ( 22 ) A , c = 2.8524 ( 5 ) A , V = 281.52 ( 9 ) A 3 , and Z = 4 . The structure was determined from a single-crystal X-ray study and refined to the conventional values R = 0.041 and w R = 0.034 for 1190 observed reflections. The framework structure is built up from edge-sharing chains of MnO6 octahedra that condense to form one-dimensional tunnels in which the sodium atoms are located. The Mn–O bond distance and bond valence analyses revealed the manganese valence Mn3+/Mn4+ ordering in the two “double rutile” chains of NaMn2O4.

We report a site selective Cu-NMR study on underdoped Hg-based five-layered high-${T}_{c}$ cuprate ${\mathrm{HgBa}}_{2}{\mathrm{Ca}}_{4}{\mathrm{Cu}}_{5}{\mathrm{O}}_{12+\ensuremath{\delta}}$ with a ${T}_{c}=72\text{ }\text{ }\mathrm{K}$. Antiferromagnetism (AFM) has been found to take place at ${T}_{\mathrm{N}}=290\text{ }\text{ }\mathrm{K}$, exhibiting a large antiferromagnetic moment of $0.67--0.69{\ensuremath{\mu}}_{\mathrm{B}}$ at three inner planes (IP). This value is comparable to the values reported for nondoped cuprates, suggesting that the IP may be in a nearly nondoped regime. Most surprisingly, the AFM order is also detected with ${M}_{\mathrm{AFM}}(\mathrm{OP})=0.1{\ensuremath{\mu}}_{\mathrm{B}}$ even at two outer planes (OP) that are responsible for the onset of superconductivity (SC). The high-${T}_{c}$ SC at ${T}_{c}=72\text{ }\text{ }\mathrm{K}$ can uniformly coexist on a microscopic level with the AFM at OP's. This is the first microscopic evidence for the uniform mixed phase of AFM and SC on a single ${\mathrm{CuO}}_{2}$ plane in a simple environment without any vortex lattice and/or stripe order.

We present point contact tunneling spectroscopy measured on nearly optimally‐doped HgBa2Ca2Cu3Oy (Hg1223) with TC∼132K. The tunneling conductances on Hg1223 exhibit two kinds of gaps that originate from crystallographically inequivalent inner four‐fold CuO2 plane (IP) and outer five‐fold CuO2 planes (OP). The averaged‐gap magnitude at OP, Δav(OP), is 37.8 meV but that at IP, Δav(IP), is 55.9 meV. This result shows that in multilayered cuprates such as Hg1223 the superconducting density of states at IP is different from that at OP, suggesting the existence of two Fermi surfaces.

63 Cu NMR measurements have been carried out in HgBa 2 Ca 2 Cu 3 O 8+δ (Hg1223) with the highest transition temperature, T c = 133 K, to date. The narrow NMR spectrum and the small residual density of states (DOS), N res , at the Fermi level in the superconducting state indicate that the Hg1223 possesses good quality.

We have measured the temperature dependence of the reversible magnetization of a four-layered cuprate $\mathrm{Tl}{\mathrm{Ba}}_{2}{\mathrm{Ca}}_{3}{\mathrm{Cu}}_{4}{\mathrm{O}}_{y}$ (Tl-1234) for the $H\ensuremath{\Vert}c$ axis, which has the highest superconducting transition temperature ${T}_{c}$ of almost $130\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ among the four-layered cuprates. The reversible magnetization was analyzed by using the high-field scaling theory and the Hao-Clem model. It was found that in the critical region around ${T}_{c}$, two-dimensional fluctuations dominate. This enhanced 2D behavior can be naturally explained by selective doping model, where doping levels of the inner and outer $\mathrm{Cu}{\mathrm{O}}_{2}$ planes in a unit cell are different. From these analyses, various thermodynamic parameters, such as the coherence length, the penetration depth, the critical fields, and the Ginzburg-Landau parameter were obtained.

We report a coexistence of superconductivity and antiferromagnetism in five-layered compound ${\mathrm{HgBa}}_{2}{\mathrm{Ca}}_{4}{\mathrm{Cu}}_{5}{\mathrm{O}}_{y}$ (Hg-1245) with ${T}_{c}=108\mathrm{K},$ which is composed of two types of ${\mathrm{CuO}}_{2}$ planes in a unit cell; three inner planes (IP's) and two outer planes (OP's). The Cu-NMR study has revealed that the optimally doped OP undergoes a superconducting (SC) transition at ${T}_{c}=108\mathrm{K},$ whereas the three underdoped IP's do an antiferromagnetic (AF) transition below ${T}_{N}\ensuremath{\sim}60\mathrm{K}$ with the Cu moments of $\ensuremath{\sim}(0.3--0.4){\ensuremath{\mu}}_{B}.$ Thus bulk superconductivity with a high value of ${T}_{c}=108\mathrm{K}$ and a static AF ordering at ${T}_{N}=60\mathrm{K}$ are realized in the alternating AF and SC layers. The AF-spin polarization at the IP is found to induce the Cu moments of $\ensuremath{\sim}0.02{\ensuremath{\mu}}_{B}$ at the SC OP, which is the AF proximity effect into the SC OP.

We report the synthesis, superconducting properties and X-ray diffraction of a single-phase “1223” superconductor, i.e. Hg0.75Ba2Ca2.05Cu3.2O8+δ having a Tc of 102 K (as-synthesized sample) and 133 K (oxygen-annealed sample). The X-ray diffraction patterns of the 102 K phase and the 133 K phase both indicate a nearly perfect single phase, corresponding to the crystal structural arrangement of the Hg-1223 compound. The as-synthesized sample has the lattice constants a=3.848(1) A and c=15.779(0) A . A slight contraction in the c-axis is observed for oxygen-annealed samples. The resulting oxygen nonstoichiometry appears to play an important role in the enhancement of Tc from 102 to 133 K.

Phosphorus (P), an element of the fifth group in the periodic table, has three main allotropes: white, red, and black. P as electrode materials for Na cells has a considerable advantage in terms of materials abundance and relatively small volume change by sodiation as Na binary compounds and alloys.[1] However, the volumetric change of P upon sodiation/de-sodiation cycles at low voltage (0.3 - 0.7 V vs. Na/Na+) caused electrolyte degradation which remains the main factor limiting the cycling life of electrodes.[1] The surface reactions of electrolytes with P in sodium ion cells have been examined. Coin cells (red or black P // Na) were cycled in electrolytes containing NaPF6 salt and ethylene carbonate/dimethyl carbonate solvent without and with the electrolyte additive (FEC or VC). Capacity retention is significantly better for the cells cycled with the electrolyte additive than for the cells cycled without the electrolyte additive, and the cells with the additive show high discharge capacity above 1450 mAh g-1 with the high coulombic efficiency than 98% after 25th cycles (Figure 1-A). To further examine the understanding of the formation of a solid electrolyte interphase (SEI) and of its evolution during cycling, powerful surface characterization techniques are combined for studying the electrode/electrolyte interphase of black P/AB electrodes, such as SEM, TEM, time-of-flight secondary ion mass spectrometry (TOF-SIMS), hard/soft X-ray photoelectron spectroscopy (HAXPES/SXPES). In particular, the effect of the electrolyte additives on the interphase chemistry was carefully explored by HAXPES and TOF-SIMS. The HAXPES analysis shows that organic species is enriched from the reduction of electrolyte solvents (EC, DEC) and electrolyte additives (FEC, VC) confirming a formation of SEI passive film. The thicker SEI layer was formed after cycling in additive-free electrolyte as compared to electrolyte with FEC or VC additive (Figure 1-B). TOF-SIMS studies reveal the SEI of the FEC-based electrolyte consists of only inorganic species, however the SEI of the VC-based electrolyte consists of organics and inorganics species. In addition, considerable modification of the surface morphology for the both electrodes was observed by SEM. Electrochemical impedance spectroscopy spectra and charge/discharge profiles of the P electrodes are analyzed to examine the kinetics evolution of electrochemical processes at different stages for sodiation. Further investigations on black or red P electrodes to improve its overall electrochemical performance (capacity, cyclability, coulombic efficiency, and voltage profile) are being carried out, including the electrode structures, effect of binders, and electrolyte/additive dependency. To summarize analytical and electrochemical results, we will discuss the potential of P as the advanced negative electrode in Na-ion batteries, concerning charge-transfer mechanisms and SEI properties.

We have prepared V2O3 thin films on Al2O3 (0001) substrate by RF magnetron sputtering using oxygen radical and V-metal target, and studied their electronic structures by X-ray absorption spectroscopy (XAS) and X-ray photoemission spectroscopy (XPS). The as-deposited V2O3 thin films deposited at 600 °C exhibits high crystallization by oxygen radical irradiation during deposition. The electrical resistivity decreases with increasing deposition temperature, and this result is due to decreasing electron scattering. The crystal field splitting (10Dq) of the V2O3 thin film estimated from the fitting of the V 2p XAS spectrum is larger than that of the bulk crystal. In the XPS spectrum of the valence band region, the density of state (DOS) of the orbital in the V 3d state increases at around the Fermi level. These results contribute to the lattice distortion between the thin film and the substrate.

Magnetic susceptibility and magnetization of the quasicrystal approximants Au-SM-R (SM = Si, Ge or Sn / R = Gd, Tb, Dy or Ho) are investigated. Ferromagnetic transitions are observed in all of these compounds, in contrast to the spin-glass behavior reported in similar compounds, Ag-In-R (R = Eu, Gd, Tb or Dy). Au-SM-Gd (SM = Si, Ge or Sn) exhibit a simple ferromagnetic transition at 22.5, 13 and 9 K, respectively, whereas Au-Si-(Tb, Dy or Ho) show indications of a canted ferromagnetic transition at 8.3, 5.9 and 3.8 K, respectively. The latter are attributed to a crystal electric field effect that is absent in the Gd-bearing compounds. The ferromagnetic behavior in Au-SM-R may be understood to be a consequence of the short R-R distances compared to those for Cd-R and Ag-In-R.

We report unusual magnetic and superconducting (SC) characteristics in multilayered ${\mathrm{CuO}}_{2}$ planes in Hg- and Cu-based high-${T}_{c}$ cuprates through the ${}^{63}\mathrm{Cu}\ensuremath{-}\mathrm{NMR}$ measurements. These compounds, in which the number of ${\mathrm{CuO}}_{2}$ planes (n) ranges from 3 to 5 in a unit cell, include crystallographically inequivalent outer (OP) and inner (IP) ${\mathrm{CuO}}_{2}$ plane that are surrounded by pyramidal and square oxygen, respectively. The Knight shift ${(}^{63}K)$ at the OP and IP exhibits respective characteristic temperature dependence, consistent with its own doping level. Using an experimental relation between the spin part in ${}^{63}K$ at room temperature and the doping level in a ${\mathrm{CuO}}_{2}$ layer ${N}_{h},$ we show that ${N}_{h}(\mathrm{OP})$ at the OP is larger than ${N}_{h}(\mathrm{IP})$ at the IP for all the systems and its difference $\ensuremath{\Delta}{N}_{h}{=N}_{h}(\mathrm{OP})\ensuremath{-}{N}_{h}(\mathrm{IP})$ increases as either a total carrier content $\ensuremath{\delta}$ or n increases. At $\ensuremath{\Delta}{N}_{h}'\mathrm{s}$ exceeding a critical value, the pseudogap behavior in the normal state is seen alone at the IP, and a bulk SC transition does not set in simultaneously at the IP and OP. A SC nature at the OP becomes consistent with a mean-field behavior only below ${T}_{c2}$ that is significantly lower than ${T}_{c}.$ Reduction in ${T}_{c}$ with increasing n is associated with an increase in $\ensuremath{\Delta}{N}_{h}.$ It is a rather remarkable aspect that a ${T}_{c}$ is not always reduced even though these multilayered high-${T}_{c}$ compounds are heavily overdoped. This arises, we show, because the IP remains underdoped and keeps a high value of ${T}_{c},$ while the OP is predominantly overdoped. This may be a microscopic origin for the lowest anisotropic SC characteristics reported to date in Cu-based multilayered high-${T}_{c}$ compounds.

Annealing effects in a reducing environment (flowing nitrogen) in the temperature range of $200--600\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ are reported on the high Tl content $({\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Tl}}_{x}){\mathrm{Ba}}_{2}{\mathrm{Ca}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{y}$ system, synthesized under high pressure (4.5 GPa). A considerable enhancement in ${T}_{c}$ from 97 K (as-synthesized) to $g130 \mathrm{K}$ (annealed at $550\ifmmode^\circ\else\textdegree\fi{}\mathrm{C})$ and an anomalous behavior in the resistivity with annealing is found. The results have been analyzed in the context of the loss of oxygen and Tl valence change.

Two-band superconductivity has a topology different from that in single-band superconductivity. The topology is not always stabilized in an infinitely homogeneous sample. The morphology, grain shape, and pattern of the device (topology of the superconducting materials) is effective in stabilizing the topology. In this report, we discuss a vortex having a small magnetic flux but a large winding number as one plausible topology in a two-band superconductor.

Artificially stacked structures of [(infinite layer CaCuO 2 ) k /(superconducting (Cu, C)Ba 2 CuO x :(Cu, C)-1201) l ] m were fabricated on SrCuO 2 buffer layer by means of sequential deposition of each block using pulsed laser deposition. Smooth and epitaxial growth all over the deposition cycles of (Cu, C)-1201 and CaCuO 2 were confirmed by streak patterns of in situ RHEED. In comparison with (Cu, C)-1201 single layer films, the artificial stacking resulted in a rise of superconducting properties, T c - onset and T c ( ρ =0) up to 95 K and 65 K, respectively.

We propose a new method to investigate the symmetry of superconducting gap function in the cuprate superconductors through phonon spectrum. A superconducting gap interference in a phonon makes a structure even in d-wave pairing as well as s-wave pairing. It is attributed to a resonance between the phonon propagating along the ab-plane and the quasi-particle excitation above the superconducting gap. This structure is demonstrated by the calculation in a clean limit. A structure was observed in an apical oxygen mode of Cu x Ba 2 Ca 3 Cu 4 O y (Cu-1234) which may be attributed to it.

We report on a possible onset of magnetism in F-substituted four-layered high- T c compounds Ba 2 Ca 3 Cu 4 O 8 (O 1− y F y ) 2 (2 y = 1.2, 1.4, 1.6 and 2.0) which are composed of two types of CuO 2 planes in a unit cell; two inner planes (IP’s) and two outer planes (OP’s). The Cu NMR study has revealed that the hole density at the OP’s is slightly larger than that at the IP’s, and a total carrier density decreases as F content increases. The F NMR study has probed the antiferromagnetic order below T N ≃ 100 K in 0234F(2.0) which undergoes a superconducting transition below T c = 55 K. This result gives evidence for the coexistence of antiferromagnetism and superconductivity even in four-layered high- T c cuprates as well as for five-layered Hg-based multilayered high- T c cuprates.

A multilayered cuprate superconductor with a nominal composition of HgBa 2 Ca 9 Cu 10 O y has been synthesized under high-pressure. A powder sample was aligned in an epoxy resin in magnetic field. The sample was analyzed by X-ray diffraction (XRD) and magnetic susceptibility measurements. Phases from n = 6 up to 15 have been recognized in the XRD patterns. The c -axis length changes by about 3.17 A with n , which means that the crystal structure changes by a unit cell of the infinite layer CaCuO 2 . The susceptibility showed a large and sharp superconducting transition at 103 K. It suggests that the phases of n = 6–15 have almost the same T c . The behavior of T c can be explained using inhomogeneous charge distribution model in multilayered cuprates.

We report the anomalous behavior of the critical temperature T c in a five-layered cuprate superconductor of (Cu,C) Ba 2 Ca 4 Cu 5 O y . The T c decreases once from 94.7 K (as-synthesized) to 93.3 K (annealed at 460 °C under N 2 flow), and then increases to 99.0 K (annealed at 530 °C under N 2 flow). We argue that this T c change reflects the CuO 2 planes governing the bulk T c , shifting from the three inner CuO 2 planes to the two outer CuO 2 planes. A model to explain this behavior is proposed, drawing two bell-shaped curves against the oxygen content (doping state), and the T c values change along the curves from that of the inner CuO 2 plane to that of the outer one.

We report on the onset of antiferromagnetism in F-substituted four-layered high- T c compounds Ba 2 Ca 3 Cu 4 O 8 ( O 1 - y F y ) 2 ( 2 y = 1.2 , 1.4 , 1.6 and 2.0) which are composed of two types of CuO 2 planes in a unit cell; three inner planes (IPs) and two outer planes (OPs). The Cu-NMR study has revealed that the hole density at the OPs are slightly larger than that at the IPs, and a total carrier density decreases as F content increases. The observation of zero-field Cu-NMR spectra over a broad frequency range has demonstrated that antiferromagnetically ordered phases emerges at low temperatures for all compounds. This result is similar to the case for the five-layered cuprates HgBa 2 Ca 4 Cu 5 O y where the optimally doped OP undergoes a superconducting (SC) transition, whereas the three underdoped IPs do an antiferromagnetic (AFM) transition [H. Kotegawa, et al., Phys. Rev. B 64 (2001) 064515; H. Mukuda, et al., Phys. Rev. Lett. 96 (2006) 087001]. The present result gives evidence for a coexistence of antiferromagnetism and superconductivity in four-layered high- T c cuprates.

Critical current densities (Jc) and irreversibility fields (Hirr) have been estimated for (B,C)(Sr,Ba)2Ca2Cu3O9 (Tc=119K) and Ba2Ca2Cu3O6(O2.yFy) (Tc=109K) from magnetization measurements. The Jc and Hirr for (B,C)(Sr,Ba)2Ca2Cu3O9 have been considerably enhanced compared with the related materials of BSr2Ca2Cu3O9 and BSr2Ca3Cu4OII. It demonstrates that properties of the sample was strongly modified by the chemical control of Ba and/or carbon substitutions. On the other hand, 0223F system showed rather low Jc and Hirr in spite of the short spacing between CUO2 layers. 0223F system should be improved the Jc and Hirr performances by a chemical (a carrier doping) control.

We report a Cu-NMR study on under-doped Hg-based five-layered cuprate HgBa 2 Ca 4 Cu 5 O 12 + δ (Hg-1245(UD)) with a T c = 72 K . The antiferromagnetism (AFM) has been found to take place at T N = 290 K , exhibiting a large antiferromagnetic moment M AF ( IP ) of 0.67 – 0.69 μ B at three inner planes (IPs) that is comparable to the values reported for non-doped cuprates. It suggests that the IP may be in a non-doped regime. The AFM with M AF ( OP ) ∼ 0.1 μ B is also detected even at two outer planes (OPs) that are responsible for the onset of superconductivity (SC). The high- T c SC at T c = 72 K can uniformly coexist on a microscopic level with the AFM at OP layers. This is the first microscopic evidence for the uniform mixed phase of AFM and SC on a single CuO 2 plane in a simple environment without any vortex lattice and/or stripe order.

We have investigated superconductivity and structure in a gold–antimony–tellurium ternary alloy system (AuxSb1−x−yTey) synthesized under high pressure. We found that Au0.125Sb0.75Te0.125 and AuSb6Te when crystallized in simple cubic structures (α-Po type), which are reported to be semiconductors above 20 K, are superconductors with a transition temperature (Tc) of 6.7 K. The structure and Tc are mapped on an Au–Sb–Te triangular diagram. A β-Po-type rhombohedral structure appears before the crystal structure changes from As type (Sb) to α-Po type. Superconductivity is observed in the β-Po-type structure as well as in the α-Po-type structure. Tc increases with decreasing Te concentration toward the Te-free Au–Sb end of the diagram. A Tc of 8.1 K was achieved for the Au–Sb alloy with a typical composition of Au0.15Sb0.85. This Tc value is the highest among materials with the α-Po-type structure under ambient pressure. Our Au0.125Sb0.75Te0.125 sample exhibits a weak metallic behavior in resistivity. The discrepancy in the normal state resistivity behaviors between the previous study and ours must originate from a difference in the number of lattice defects in the samples.

The superconducting anisotropy of a nontoxic high-Tc (=118K) superconductor CuBa2Ca3Cu4O12-y (Cu-1234) is compared with those of such other cuprates as Cui-xMxBa2Ca3Cu4O12-y (M= Ag, Tl and Hg) and infinite layered superconductor Sri-xLaxCuO2 by using a conventional measurement method of anisotropy, and the origin of its low anisotropy was discussed. The Cu-1234 has the least superconducting anisotropy y =1.5 among cuprate superconductors. The origin of its least anisotropy comes principally from the strong superconducting coupling between superconducting Ca3Cu4O8-block layers mediated by superconducting octahedral-Cu06 charge-reservoir layer rather than the spacing between Ca3Cu4O8-block layers.

Single-phase samples of (Cu1-xMx)Ba2Ca3Cu4Oy (M=CO3, SO4, NO3) have been prepared by a high-pressure technique. At least about 56% and 24% of Cu site was found to be substituted successively for groups of CO3 and SO4 (or NO3), respectively. The c-axis length of (Cu1-xCx-1234 decreased linearly with increasing x. Carbon content x of (Cu1-xCx)-1234 is able to be estimated by the relation between the c-axis length and the carbon content x. Tc of (Cu1-xCx)-1234 for x 0.46. High-temperature X-ray diffraction analysis has revealed that Cu-1234 is decomposed above about 600 °C.

The crystal structures of three CuxBa2Ca3Cu4Oy compounds with x = 0. 62, 0. 68 and 0. 73 and oxycarbonate (Cu,C)Ba2Ca3Cu4Oy have been precisely investigated using intensity data collected on the single-crystal X-ray four-circle diffractometer. The Cu-site occupancy x in the deficient Cu(l)02 sheet between two BaO layers increases from 0. 62 to 0. 73 together with decreasing the c-axis length in CuxBa2Ca3Cu4Oy. The size of block-layer unit decreases with decreasing the c-axis length from 8. 421(4) A for x = 0. 62 to 8. 373(3) A for x = 0. 73, respectively, while the size of the infinite-layer unit is maintained unchanged. The lattice parameters and the Cu/C ratio of (Cu,C)Ba2Ca3Cu4Oy are consistent with those in the previous report.

The single crystal of CuBa2Ca3Cu4O12-y (Cu-1234) was grown under high-pressure. The single crystal with maximum size of 250×150×30μm3 was obtained at 1150°C for 30 hours under a pressure of 4. 5GPa. The lattice parameters were a=3. 860(1)A and c=17. 942(1)A with the space group of P4/mmm. The refinement of the crystal structure with R=0. 044 showed that the Cu-vacancy between two Ba-O layers was 27%. The composition was measured by SEM-EDX(energy dispersive X-ray) system. The average values of cation ratio were Ba:Ca:Cu=2:3. 17:5. 07. The measurement of magnetization showed that Tc of the single crystal was 115K.

The critical current density and irreversibility line of the single-phase polycrystalline sample of CuBa2Ca3Cu4Oy with Tc=l17 K have been estimated from measurements of magnetic hysteresis loops assuming Bean critical state model. Simple power law relations, Jc∝H-m, are observed in the magnetic field dependence of the intragrain Jc. Values of the intragrain Jc in a magnetic field of 1 T are about 106 and 104 A/cm2 at temperatures of 5 and 77 K, respectively. An exponential decay of the Jc with increasing temperature, Jc∝exp(-T/T0), is observed below 60 K. The characteristic temperature T0 of Cu-1234 is T0=16.1 K in a magnetic field of 1.0 T. The dependence of the Jc on temperature is relatively small among the oxide superconductors. Simple power law relations, Jc∝(l-T/Tc)n, are found in whole ranges of the temperature and magnetic field. The value of n is 5.24 for a magnetic field of 1.0 T The irreversibility fields at 70 and 77 K are estimated to be 9.5 and 3.7 T, respectively. The temperature dependence of the Hirr is fitted by Hirr=a(l-T/Tc)n with a=2130 and n=5.91.

Samples with different fractions of structural modulation were synthesized in order to study the effect of a defective modulated structure on the critical temperature T c of Hg-1234. Electron microscopy revealed the existence of modulated and unmodulated Hg-1234 structures in these samples. Measurements of critical temperature T c on these samples revealed that the structural modulation significantly suppresses the T c . For the Hg-1234 sample without the structural modulation, the T c was found to be close to the highest T c for the Hg-1223 phase.

Nearly single phase polycrystalline samples of (Cu,Ag)Ba2Ca3Cu4Oy and CuxBa2Ca3Cu4Oy have been synthesized by a high-pressure synthesis method. The samples were characterized by X-ray diffraction analysis and electrical resistivity measurements. The magnetic field dependence of intragrain Jc for as-sintered and proton irradiated samples was estimated from measurements of magnetic hysteresis using Bean critical state model. Improvement of Jc by proton irradiation was observed at low temperature below 40 K. The intragrain Jc at 5 K and 5 T was enhanced from 105 A/cm2 to 106 A/cm2.

A high-Tc, nontoxic and low anisotropic superconductor CuBa2Ca3Cu4O12−δ (Cu-1234) has been synthesized by solid state reaction under high pressure using a pure precursor Ba2Ca3Cu4O9 and CaO2. In order to eliminate the carbonate and the hydroxide, we have used the precursor material Ba2Ca3Cu4O9 sintered above 920 °C and pure CaO2 prepared from CaO2 · 8H2O. Nearly single phase CuBa2Ca3Cu4O12−δ samples were successfully synthesized at 1000°C under 4 GPa. The sample has shown distorted tetragonal cell with the lattice constants of a=3.855(7) A and c=17.993(9) A, a superconducting transition(Tc) at 117 K and anisotropic parameter γ = ξ ab / ξc =1.6.

The crystal structures of Cu1−xBa2Can−1CunO2n+4−y were investigated by a single-crystal X-ray diffraction method. Single crystals (maximum size: 0.1 × 0.1 × 0.01 mm) of Cu-1234 (n=4) and Cu-1245 (n=5) phases have been synthesized using a high-temperature and high-pressure technique. The X-ray precession photographs showed the basic structures may be chosen as tetragonal primitive lattices; α = 3.8526(18) A, c = 17.973(5) A for Cu-1234, and α = 3.8577(5) A, c = 21.1546(14) A for Cu-1245, respectively. The weak superstructure spots, observed in the X-ray precession photographs in both compounds, can be explained by the micro-twin structures determined by electron diffraction.

We have carried out zero-field muon spin relaxation (ZF-μSR) measurements in multi-layered HgBa 2 Ca 4 Cu 5 O y (Hg-1245) superconductor with T c of 108 K. The variation of ZF-μSR time spectra from Gaussian-type to exponential-type behavior was observed with decreasing temperature below 60 K and the muon precessions were also observed below 45 K. These results indicate the appearance of a static magnetic order of Cu moments at muon sites below T c . Compared with the results of NMR measurements, they suggest that this magnetic order is caused in three under-doped inner planes of five CuO 2 planes in Hg-1245.

We pointed out a soliton can be present in a multi-band superconductor [Phys. Rev. Lett. 88 (2002) 017002]. We named it i -soliton. It connects two different coherent states having different phases. Simultaneously the time reversal symmetry breaks down. The i -soliton traps a fractional flux inside a superconducting loop. These properties may realize a fractional flux quantum device without Josephson junction in a real space. It is beyond a single flux quantum device. The i -soliton would be found in the multi-layer cuprate superconductor having crystallographically nonequivalent CuO 2 planes in one unit cell of which representative is Cu x Ba 2 Ca 3 Cu 4 O y (Cu-1234).

Anomalous suppression of Tc has been found in an overdoped region of TlBa2Ca2Cu3O9−δ superconductors. A heavily overdoped sample (Tc≃100 K) was synthesized under high pressure. The Tc was measured with decreasing the oxygen content until the sample becomes optimally doped state with a Tc≃131 K. A dip of Tc was observed before the Tc reaches to an optimal value i.e. in an overdoped region. This behavior is quite strange because Tc is known to change monotonically in an overdoped region. Some possible explanations for this anomalous behavior will be presented.

As the temperature is lowered below Tc (107 K), a remarkable increase of the thermal conductivity, having a broad maximum, was observed. The behavior of the temperature dependence of the enhancement below Tc seems to be correlated to specific characteristics relating to a coexistence of magnetic and superconducting state in this compound.

Annealing effect of the irreversibility fields ( H irr ) in (Cu,C)Ba 2 Ca 2 Cu 3 O y ((Cu,C)-1223) and (Cu,C)Ba 2 Ca 3 Cu 4 O y ((Cu,C)-1234) have been investigated. The samples prepared under high pressure were post-annealed in nitrogen gas in the temperature range of 400–500 °C. H irr of (Cu,C)-1234 was improved after annealing at 450 °C while T c remained almost constant. This suggests that carrier density of five-coordinated CuO 2 planes or conductivity of charge reservoir layers is changed by annealing while keeping that of four-coordinated CuO 2 planes almost constant. Both samples show H irr ≃4 T at 90 K by the post-annealing, which is quite attractive for practical application.

We report a coexistence of superconductivity and antiferromagnetism in HgBa 2 Ca 4 Cu 5 O y with T c =108 K trough Cu-NMR measurements. This compound is composed of two kinds of CuO 2 planes in a unit cell, three inner planes (IP) and two outer planes (OP). The OP is optimally-doped, undergoing a superconducting transition at T c =108 K, whereas the IP is strongly underdoped, doing an antiferromagnetic transition below T N ∼60 K.

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