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Effects of Mn-substitution on magnetic properties of Zn1-xMnxO (MZO) nanoparticles with x= 0.00, 0.03, 0.05 and 0.07 have been investigated along with their local structure. Study on Mn K-edge XANES spectra of MZO reveals that the oxidation state increases by Mn-substitution, which further implies that MZO exhibits a mixed valence state of Mn3+/Mn4+. The local structure analysis on Mn K-edge EXAFS spectra shows that the coordination number (CN) of Mn reduces by increasing Mn concentration, thus the amount of oxygen vacancy (VO) increases by Mn-substitution. Interestingly, the magnetization of MZO also tend to increase as the Mn concentration increases. The M(H) curves exhibit a linear (paramagnetic) behavior, showing no evidence of room-temperature ferromagnetism. Our results show that magnetism of MZO is related to the correlation between Mn magnetic moment and VO.

Some studies of the usage of biomass to produce carbon-based compounds have been reported in the past. Here we report that palmyra sugar can be one of the sources to produce amorphous carbon (a-C) from biomass after the heating treatment at 250°C. In this paper, X-Ray Diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX), Fourier Transform Infrared (FTIR) and Superconducting Quantum Interference Device (SQUID) measurements are reported in order to check the detailed properties of a-C from palmyra sugar. The XRD data at a diffraction peak position (2θ) of ~23o support the formation of a-C. The functional groups detected by FTIR spectra consist of C=C, C-C, C-O, C=O, C-H and O-H. The remnant magnetization (Mr), coercive field (Hc) and saturation magnetization are estimated as ~0.1 10-3 emu/g, ~50 Oe and ~9 10-3 emu/g, respectively. Soft ferromagnetism in a-C from palmyra sugar is confirmed, comparable with the magnetization result in the reduced graphene oxide (rGO) sample from coconut shell and rGO commercial material which have the same mixture hybridization. Some studies of the usage of biomass to produce carbon-based compounds have been reported in the past. Here we report that palmyra sugar can be one of the sources to produce amorphous carbon (a-C) from biomass after the heating treatment at 250°C. In this paper, X-Ray Diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX), Fourier Transform Infrared (FTIR) and Superconducting Quantum Interference Device (SQUID) measurements are reported in order to check the detailed properties of a-C from palmyra sugar. The XRD data at a diffraction peak position (2θ) of ~23o support the formation of a-C. The functional groups detected by FTIR spectra consist of C=C, C-C, C-O, C=O, C-H and O-H. The remnant magnetization (Mr), coercive field (Hc) and saturation magnetization are estimated as ~0.1 10-3 emu/g, ~50 Oe and ~9 10-3 emu/g, respectively. Soft ferromagnetism in a-C from palmyra sugar is confirmed, comparable with the magnetization result in the reduced graphene oxide (rGO) sample from coconut shell and rGO commercial material which have the same mixture hybridization.

Non-doped and strontium-doped lanthanum cuprates (La2CuO4 (LCO) and La1.85Sr0.15CuO4 (LSCO15)) in nano-sized particles were synthesized by the chemically dissolved technique employing HNO3 as the dissolving agent. The structural and magnetic properties were investigated by using an x-ray diffraction (XRD) apparatus and a superconducting quantum interference device (SQUID) magnetometer, respectively. The XRD patterns of LCO and LSCO15 show the formation of the single phase without impurities after the calcinations in air at 1100°C for 15 h and the post-annealing in oxygen at 800 °C for 24 h. The average crystallite sizes of LCO and LSCO15 samples were in a range of around 100 nm confirming nano-sized particles. The LCO and LSCO15 nanoparticles exhibit superconductivity at the superconducting (SC) transition temperature, Tc, of 23 K and 38 K, respectively. The magnetization curve measurements have revealed that both samples show the appearance of ferro- and dia-magnetic behavior at room temperature and the appearance of superconductivity at low temperatures. This result may indicate the coexistence of ferromagnetism and superconductivity below Tc in the nano-sized cuprates.

In $T$*-type cuprate oxides with five oxygen coordination, little is known about the relationship between the spin correlations and dope carriers. We performed $^{139}$La-nuclear magnetic resonance (NMR) and electrical resistivity measurements on an as-sintered (AS) and oxidation annealed (OA) polycrystalline $T$*-type La$_{0.86}$Eu$_{0.86}$S$_{0.28}$CuO$_4$ (LESCO) to investigate its magnetic and superconducting (SC) properties. Upon cooling, the NMR spectrum of AS LESCO broadened below 3 K, at which the nuclear spin-lattice relaxation rate $1/T_1$ against the temperature exhibited a maximum, thereby indicating the appearance of static magnetism. The temperature dependence of $1/T_1$ between 3 K and 20 K was similar to that of the resistivity displaying the semiconducting behavior. Furthermore, the energy scale of the transport gap and spin-dynamics estimated was found to be comparable. These results suggest a close connection between the mobility of the doped carriers and low-energy spin-dynamics, as reported for lightly doped $T$-type La$_{2-x}$Sr$_x$CuO$_4$. In the OA SC sample, we confirmed the absence of a magnetic order and the Korringa relation above 10 K. Therefore, in the $T$*-type LESCO with $x$ = 0.28, the magnetic state coupled with holes drastically turns to the weakly correlated metallic state by oxidation annealing., Comment: 6 pages, 6 figures

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.

We have investigated the effect of the Sr-substitution for Ba on the superconductivity in Yb0.6Ca0.4Ba2-ySryCu3O6 without Ochain forming the so-called Cu(1)O chain in the blocking layer. It has been found that Tc increases with increasing y even though no holes are doped through the Sr2+-substitution for Ba2+. The increase in Tc is because holes doped by the Ca-substitution for Yb are more likely supplied to the superconducting Cu(2)O2 plane than the blocking layer of Cu(1) owing to the contraction of the Cu(2)O2 plane through the substitution of smaller Sr2+ for larger Ba2+. The highest Tconset = 73 K observed for y(Sr) = 0.6 is greatly higher than the previous record of Tconset = 50 K in (RE,Ca)Ba2Cu3O6 (RE: rare-earth element). The reason why it is lower than ∼90 K for REBa2Cu3O7 is the low hole-concentration in the Cu(2)O2 plane.

Recently, the so-called room-temperature ferromagnetism in any nanoparticles has been studied intensively. It is well known that the properties of ferromagnetism and superconductivity are contradictory in a superconducting high-Tc cuprate. The existence of ferromagnetism in the nanoparticles has been suggested to occur on the surface. This magnetism has been expected to come from defects inducing magnetic moments on oxygen vacancies at the surface of the nanoparticles. This work is to observe magnetism in nanosized superconducting Pr2-xCexCuO4 (PCCO) with x = 0.15 by means of a superconducting quantum interference device (SQUID). The magnetization curves of the reduced PCCO nanoparticles with the superconducting transition temperature, Tc, of ~25 K have revealed that there is weak ferromagnetism observed at room temperature. The magnitude of magnetization could be enhanced by oxygen reduction annealing in vacuum with increasing annealing temperature. A non-linear magnetization occurring in the reduced PCCO nanoparticles through the vacuum annealing process is probably due to a strong oxygen reduction producing more oxygen vacancies in the T'-structure.

We have succeeded in synthesizing electron-doped polycrystalline bulk samples of T'-La1.8Eu0.2CuO4-yFy (y = 0 - 0.15) by the fluorination of undoped (Ce-free) T'-La1.8Eu0.2CuO4 using NH4F. The magnetic susceptibility measurements have revealed that the superconducting transition temperature, Tc, increases with increasing y, exhibits the maximum of 23 K at y = 0.025, and decreases. The dome-like dependence of Tc on the doped carrier concentration in the T'-type (La,Eu)-based cuprates is explained in terms of the pairing mediated by spin fluctuations based on the d-p model calculation [K. Yamazaki et al., J. Phys.: Conf. Ser. 871, 012009 (2017)]., 14 pages, 5 figures

Magnetic properties of reduced T’-Pr2-xCexCuO4 (T’-PCCO) nanoparticles with x = 0, 0.10, and 0.15 have been investigated. The T’-PCCO samples were synthesized by the chemically dissolved method with HNO3 as dissolving agents and by the succeeding calcination at 1000 °C for 15 h in air. The reduced T’-PCCO samples were obtained by the reduction annealing at 700 °C for 10 h in Argon atmosphere and at 700 °C for 12 h in vacuum. Rietveld analyses of the X-ray diffraction (XRD) patterns for all the samples have revealed dependences of the c-axis length and the crystal size on the Ce doping and the reduction annealing. XRD analyses and transmission electron microscopy (TEM) images have confirmed T’-PCCO nanoparticles with the size of around 40–100 nm. Magnetic properties of all the T’-PCCO nanoparticles were studied by a superconducting quantum interference device (SQUID) showing a dominant paramagnetic feature with very weak ferromagnetism in the as-synthesized samples at room temperature. It has changed to a pure paramagnetic feature after the reduction annealing in argon atmosphere and an enhanced ferromagnetism through vacuum annealing. This is probably due to the change in the number of oxygen vacancies through the defect recovery and the removal of excess oxygen after both reduction annealing processes, respectively.

One of the key challenges in condensed-matter physics is to establish a topological superconductor that hosts exotic Majorana fermions. Although various heterostructures consisting of conventional ...

Polycrystalline samples of the Bi-based cuprate superconductors Bi2Sr2-x-yBaxLayCuO6+δ (y(La) = 0, 0.4, 0.6) have been prepared by the conventional solid-state reaction method to increase the superconducting transition temperature, Tc, in the so-called Bi-2201 phase. It has been found that the solubility limit of Ba is x(Ba) = 0, 0.2 and 0.3 for y(La) = 0, 0.4 and 0.6, respectively. Accordingly, the La-substitution for Sr is effective for the Ba-substitution for Sr. Superconductivity has also been observed for the Ba-substituted samples, but the increase in Tc through the Ba-substitution is only a few Kelvins.

Effect of co-substitution of Ca and Sr in the Y-124 phase of Y1-x CaxBa2-y Sr y Cu4O8 has been investigated. Polycrystalline samples of Y1-x CaxBa2-y Sr y Cu4O8 with 0 ≤ x(Ca) ≤ 0.2 and 0 ≤ y(Sr) ≤ 0.2 have been prepared by the molten KOH method. The lattice parameters decrease with increasing y(Sr), indicating that the smaller Sr ions are systematically substituted for the larger Ba ions. The value of Tc increases from 83 K to ∼ 90 K through the Sr-substitution for x(Ca) = 0, while Tc ∼ 90 K are almost independent of y(Sr) for x(Ca) = 0.1 and 0.2.

Polycrystalline samples of the Bi-2212 phase of Bi2−x Pb x Sr2CaCu2O8−z F z with x(Pb) = 0.6 and 1.0 have been prepared. All the samples are almost of the single phase with the Bi-2212 structure for x(Pb) = 0.6. The value of Tc ∼ 82 K for z(F) = 0 increases up to 86–88 K for z(F) = 0.2–0.6. This may be due to the decrease in the amount of vacancy at the O-site by the introduction of F−. In addition, we have successfully synthesized the partially Ba-substituted Bi-2212 phase of Bi1.4Pb0.6Sr2−y Ba y CaCu2O7.8F0.2 with 0 ≤ y(Ba) ≤ 0.5. Tc increases up to 98 K for y(Ba) = 0.5. The enhancement of Tc through the Ba-substitution may be due to the increase in the distance between Cu and the apical oxygen.

Fluctuations of various order parameters are considered as the significant components of understanding the mechanism of high-Tc superconductivity. To study these fluctuations in the cuprate and Fe-based superconductors we use the joint measurements of direct current resistivity and non-resonant microwave absorption. Comparing data obtained with both methods allowed us to extract the contribution of dynamic charge density waves in La2−xSrxCuO4, superconducting fluctuations in Bi2Sr2Ca1−xYxCu2O8 and nematic fluctuations in FeTe1−xSex. © Kazan Federal University (KFU). Government Council on Grants, Russian Federation Government Council on Grants, Russian Federation Russian Academy of Sciences, RAS Kazan Federal University This work was supported by the Russian Academy of Sciences via the grant of Program 1.12 “Fundamental Problems of High-Temperature Superconductivity”. The work of D.Ch. is supported by the program 211 of the Russian Federation Government, agreement No. 02.A03.21.0006 and by the Russian Government Program of Competitive Growth of Kazan Federal University. The work of A.V. has been supported by Act 211 of the Government of Russian Federation, Contracts No. 02.A03.21.0006 and No. 02.A03.21.0011.

We have measured temperature and magnetic field dependences of the thermal conductivity along the c-axis, kc, and that along the [110] direction, k110, of CuB2O4 single crystals in zero field and magnetic fields along the c-axis and along the [110] direction. It has been found that the thermal conductivity is nearly isotropic and very large in zero field and that the thermal conductivity due to phonons is dominant in CuB2O4. The temperature and field dependences of kc and k110 have markedly changed at phase boundaries in the magnetic phase diagram, which has been understood to be due to the change of the mean free path of phonons caused by the change of the phonon-spin scattering rate at the phase boundaries. It has been concluded that thermal conductivity measurements are very effective for detecting magnetic phase boundaries., Comment: 18 pages, 6 figures

New superconductors, Lix(C2H8N2)yMoTe2 with 0 < x(Li) ≤ 1, have been synthesized via the co-intercalation of Li and ethylenediamine (EDA) into MoTe2. It has been found that the maximum \(T_{\text{c...

Iron-chalcogenide-based superconductors have attracted much attention due to their relatively high superconducting transition temperatures ( T c ) and their simple layered crystal structures. We have performed electrochemical co-intercalation of Na and propylene carbonate (PC) into FeSe, and successfully synthesized a new superconductor, Na x (PC) y Fe 2 Se 2 , with T c = 43 K. The type and amount of intercalated metal, and the electrolyte used in the intercalation affected the superconductivity. Our electrochemical intercalation method should be a useful tool for discovering new superconductors by controlling the intercalation conditions.

New superconductors, Li$_x$(C$_n$H$_{2n+3}$N)$_y$Fe$_{1-z}$Se ($n$ = 6, 8, 18), have been synthesized via the co-intercalation of linear monoamines together with Li into FeSe. The distance between neighboring Fe layers expands up to 55.7 {\AA} for n = 18, which is much larger than the previous record of 19 {\AA} in the FeSe-based intercalation superconductors. Tc remains saturated at $\sim$42 K.

We have attempted to synthesize the Bi-2212 phase of BiPbSr2−x Bax RECu2O8+δ (RE = Nd, Sm, Gd, Y, Yb) by the conventional solid-state reaction method. The completely Ba-substituted sample with x = 1 has been successfully synthesized only for Nd. As the ionic radius of RE decreases, the solubility limit of Ba decreases. It has been found that the substitution of Ba for Sr requires the expansion of both the Bi–O and RE layers as well as the synthesis in a reducing atmosphere to suppress the formation of BaBiO3-related phases. Unfortunately, the hole-doping to semiconducting BaPbBa2NdCu2O8+δ has not been successful.

We investigated the temperature dependence of resistivity in thin crystals of FeSe1−xTex (x = 1.0, 0.95, and 0.9), though bulk crystals with 1.0 ≧ × ≧ 0.9 are known to be non-superconducting. With decreasing thickness of the crystals, the resistivity of x = 0.95 and 0.9 decreases and reaches zero at a low temperature, which indicates a clear superconducting transition. The anomaly of resistivity related to the structural and magnetic transitions completely disappears in 55- to 155-nm-thick crystals of x = 0.9, resulting in metallic behavior in the normal state. Microbeam x-ray diffraction measurements were performed on bulk single crystals and thin crystals of FeSe1−xTex. A significant difference of the lattice constant, c, was observed in FeSe1−xTex, which varied with differing Te content (x), and even in crystals with the same x, which was mainly caused by inhomogeneity of the Se/Te distribution. It has been found that the characteristic temperatures causing the structural and magnetic transition (T t), the superconducting transition (T c), and the zero resistivity (T c zero) are closely related to the value of c in thin crystals of FeSe1−xTex.

Polycrystalline samples of Lu0.5Ca0.5Ba1.4Sr0.6Cu3O6 without oxygen in the blocking layer of the so-called Cu(1)O chain have been prepared by the conventional solid-state reaction method. The onset temperature of the superconducting transition Tconset = 80 K observed in the magnetic susceptibility measurement for the sample with the oxygen content of 5.87 is the highest record in the REBa2Cu3O6 (RE: rare-earth element) phase. The hole concentration in the superconductive Cu(2)O2 plane estimated from the thermoelectric power at R. T. is about 0.12 (/Cu(2)), indicating that the sample is still situated in the underdoped region. We have also investigated the effect of the introduction of oxygen into the blocking layer on Tc. It has been found that Tc takes a minimum at 6 + δ ~ 6.1 and the maximum at 6 + δ ~ 6.5 in Lu0.5Ca0.5Ba1.4Sr0.6Cu3O6+δ.

We demonstrate the presence of ferromagnetic (FM) fluctuations in the superconducting and nonsuperconducting heavily overdoped regimes of high-temperature superconducting copper oxides, using $(\mathrm{Bi},\mathrm{Pb}{)}_{2}{\mathrm{Sr}}_{2}{\mathrm{CuO}}_{6+\ensuremath{\delta}}$ (Bi-2201) single crystals. Magnetization curves exhibit a tendency to be saturated in high magnetic fields at low temperatures in the heavily overdoped crystals, which is probably a precursor phenomenon of a FM transition at a lower temperature. Muon spin relaxation detects the enhancement of spin fluctuations at high temperatures below 200 K. Correspondingly, the $ab$-plane resistivity follows a $4/3$ power law in a wide temperature range, which is characteristic of metals with two-dimensional FM fluctuations due to itinerant electrons. As the Wilson ratio evidences the enhancement of spin fluctuations with hole doping in the heavily overdoped regime, it is concluded that two-dimensional FM fluctuations reside in the heavily overdoped Bi-2201 cuprates, which is probably related to the decrease in the superconducting transition temperature in the heavily overdoped cuprates.

We have succeeded in synthesizing new intercalation superconductors Lix(C2H8N2)yMoSe2 and Lix(C6H16N2)yMoSe2 with Tc = 4.2 and 3.8-6.0 K, respectively, via the co-intercalation of lithium and ethylenediamine or hexamethylenediamine into semiconducting 2H-MoSe2. It has been found that the Tc values are related not to the interlayer spacing between MoSe2 layers so much but to the electronic density of states (EDOS) at the Fermi level. Moreover, only Li-intercalated LixMoSe2 with a small interlayer spacing has been found to be non-superconducting. Accordingly, it has been concluded that not only a sufficient amount of EDOS at the Fermi level due to the charge transfer from intercalated Li to MoSe2 layers but also the enhancement of the two-dimensionality of the crystal structure and/or electronic structure due to the expansion of the interlayer spacing between MoSe2 layers is necessary for the appearance of superconductivity in MoSe2-based intercalation superconductors. The pairing mechanism and the analogy to the superconductivity in the electric double-layer transistors of 2H-MoX2 (X = S, Se, Te) are discussed., Comment: 17 pages, 8 figures, 1 tabele. arXiv admin note: substantial text overlap with arXiv:1709.03779

The magnetic field distribution on the surface of the high-Tc superconductor crystals Bi2Sr2Ca1−x Y x Cu2O8+y has been studied in a wide temperature range using electron paramagnetic resonance (EPR) of the surface probe. The changes of the EPR signal broadening and shift with temperature and the probe-sample distance have been investigated. The analysis of obtained data made it possible to conclude that in the large temperature range above the critical temperature, some of the studied crystals are magnetized inhomogeneously. In the samples underdoped with charge carriers, the range is 40 K. Such samples contain inclusions with diamagnetic and paramagnetic magnetization. They are probably formed due to the electron phase separation.

We demonstrate the presence of ferromagnetic (FM) fluctuations in the superconducting and nonsuperconducting heavily overdoped regimes of high-temperature superconducting copper oxides, using (Bi,Pb)_{2}Sr_{2}CuO_{6+δ} (Bi-2201) single crystals. Magnetization curves exhibit a tendency to be saturated in high magnetic fields at low temperatures in the heavily overdoped crystals, which is probably a precursor phenomenon of a FM transition at a lower temperature. Muon spin relaxation detects the enhancement of spin fluctuations at high temperatures below 200 K. Correspondingly, the ab-plane resistivity follows a 4/3 power law in a wide temperature range, which is characteristic of metals with two-dimensional FM fluctuations due to itinerant electrons. As the Wilson ratio evidences the enhancement of spin fluctuations with hole doping in the heavily overdoped regime, it is concluded that two-dimensional FM fluctuations reside in the heavily overdoped Bi-2201 cuprates, which is probably related to the decrease in the superconducting transition temperature in the heavily overdoped cuprates.

We have succeeded in synthesizing hole-doped bulk superconductors of La 1.8-x Eu 0.2 Ca x CuO 4 ( x = 0.05 and 0.10) with the Nd 2 CuO 4 -type structure by means of the structural transformation at low temperatures from the K2NiF4-type structure via the Nd 4 Cu 2 O 7 -type structure. Superconductivity has appeared through the removal of excess oxygen by the reduction annealing in vacuum. Values of the superconducting transition temperature, T c , are 13 and 6 K for x = 0.05 and 0.10, respectively. These values are smaller than those of T’-La 1.8-x Eu 0.2 Sr x CuO 4 .

We investigated the magnetism and superconductivity in as-sintered (AS) and oxidation annealed (OA) T*-type La1−x/2Eu1−x/2SrxCuO4 (LESCO) with 0.14 ≤ x ≤ 0.28 by the first comprehensive muon spin r...

We have developed a simple method of the synthesis of hydrides using CaH2 as a hydrogen source. The perovskite-type hydrides A PdH 3-x ( A = Sr, Ba) have successfully been synthesized this method. However, no superconductivity has been observed above 2 K.

We have performed scanning photoelectron spectromicroscopy measurements in the paramagnetic (PM) and the antiferromagnetic (AFM) phases of Fe1+δTe (δ = 0.09). The spectromicroscopy images reveal stripe modulation of the electronic structure in the AFM monoclinic phase at low temperature, that disappears at high temperature in the PM phase. The stripes, running along the monoclinic crystal axis, are characterized by different density of states around the Γ point and near the Fermi level (EF). Since the near EF electronic states around the Γ point have strong electron–lattice coupling in Fe1+δTe, the observed stripes are likely to be related to the strain modulation introduced by the monoclinic lattice distortion.

We have studied the electronic structure of FeSe1−xTex and Ir1−xPtxTe2 using photoemission spectroscopy. For FeSe1−xTex, angle-resolved photoemission results indicate that the Fe 3d yz/zx orbital degeneracy at Γ point and orbitally induced Peierls effect in the tetragonal lattice play important roles for the superconductivity. It is suggested that the Jahn-Teller instability of the yz/zx states couples with local lattice distortion derived from the Te substitution for Se and provides an inhomogeneous electronic state. Photoemission results of IrTe2 with triangular lattice are also consistent with the orbitally induced Peierls scenario. The Pt substitution for Ir suppresses the static band Jahn–Teller effect and induces an inhomogeneous electronic state in which orbital (or bond or nematic) fluctuations may help superconductivity through the Peierls effect.

Our Recent Works on the Search for New Superconductors Using Soft-Chemical Techniques Are Reviewed. We Have Found New Mg-Intercalated Superconductors of MgxZrNCl and MgxHFNCl with Tc ~ 13 K and 25 K, Respectively. Moreover, we Have Succeeded in Preparing Bulk Samples of Hole-Doped (La,Ca)2CuO4 with the Nd2CuO4-Type, Namely, the so-Called T’-Type Structure by Reduction of (La,Ca)2CuO4 with the K2NiF4-Type, Namely, the so-Called T-Type Structure Using CaH2 at a Temperature as Low as 300°C and Subsequent Oxidation. This Result Is in Contrast with the Synthesis of (La,Ca)2CuO4 with the K2NiF4-Type Structure by the Conventional Solid-State Reaction Method at a Temperature as High as ~1000°C.

We have successfully synthesized a new superconductor EuSr 2 Cu 2 Ta 1− x Sn x O 8− y of the so-called Ta-1212 system, where Ta is substituted for Cu(1) in the Y-123 type structure and holes are doped into the CuO 2 plane through the partial substitution of Sn 4+ for Ta 5+ . The superconducting transition temperature, T c , is about 40 K at x = 0.2. This is the first superconductor in the Ta-1212 system.

Specific heat has been measured in magnetic fields at low temperatures down to 0.4 K in the iron-chalcogenide superconductors of FeSe 1− x Te x , in order to investigate details of the superconducting (SC) gap. Using the two-gap model, it has been found that the smaller SC gap is significantly depressed by the application of magnetic field. Moreover, it has been found that the enhancement of the residual electronic-specific-heat-coefficient in the ground state by the application of magnetic field is much smaller than that expected for superconductors with the typical s -wave or d -wave SC paring symmetry. These results are discussed in relation to the multi-band effect in the iron-based superconductors.

Polycrystalline samples of RE 0.6Ca0.4Ba1.6Sr0.4Cu3O6 (RE = Nd, Gd, Dy, Y, Yb, Lu) without oxygen in the Cu(1)O chain have been prepared by the conventional solid-state reaction method. No superconductivity appears for larger RE = Nd, Gd, Dy, while superconductivity with T c ~50 K appears for smaller RE = Y, Yb, Lu. This is presumably because holes produced by the Ca-substitution for RE are more supplied to the conductive Cu(2)O2 plane than to Cu(1) as the lattice becomes small. The maximum T c = 53 K for RE = Lu is considerably lower than 90 K for REBa2Cu3O7. This may be due to the low hole-concentration in the Cu(2)O2 plane.

We have succeeded in synthesizing new superconductors Li x (C2H8N2) yMSe2 and Li x (C6H16N2) yMSe2 (M = Ti, Mo) with T c = 2.4 – 6.0 K via the co-intercalation of lithium and diamines into 1T-TiSe2 and 2H-MoSe2. As for M = Ti, it has been found that both the electron doping due to the Li intercalation and the expansion of the interlayer spacing between TiSe2 layers due to the intercalation of diamines suppress the charge density wave transition, leading to the appearance of superconductivity. As for M = Mo, T c has been found to be related not to the interlayer spacing but to the carrier density increased by the electron doping due to the Li intercalation.

The application of an electrochemical method to the iron-based chalcogenide superconductors has great potentials in enhancing their properties such as the superconducting transition temperature. Unfortunately, this method has been limited to polycrystalline powders or thin film samples with a large surface area. Here, we demonstrate that the electrochemical method can be usefully applied to single-crystal devices of FeSe1− x Te x superconductors by combining it with the focused ion beam (FIB) microfabrication techniques. Our results open a new route to developing the high-quality superconducting devices fabricated using layered iron-based chalcogenides, whose properties are electrochemically controlled.

We developed prototype neutron color image intensifiers with high-sensitivity, wide dynamic range and long-life characteristics. In the prototype intensifier (Gd-Type 1), a terbium-activated Gd2O2S is used as the input-screen phosphor. In the upgraded model (Gd-Type 2), Gd2O3 and CsI:Na are vacuum deposited to form the phosphor layer, which improved the sensitivity and the spatial uniformity. A europium-activated Y2O2S multi-color scintillator, emitting red, green and blue photons with different intensities, is utilized as the output screen of the intensifier. By combining this image intensifier with a suitably tuned high-sensitive color CCD camera, higher sensitivity and wider dynamic range could be simultaneously attained than that of the conventional P20-phosphor-type image intensifier. The results of experiments at the JRR-3M neutron radiography irradiation port (flux: 1.5×108 n/cm2/s) showed that these neutron color image intensifiers can clearly image dynamic phenomena with a 30 frame/s video picture. It is expected that the color image intensifier will be used as a new two-dimensional neutron sensor in new application fields.

We have measured the temperature dependence of the magnetic susceptibility, χ vs. T, and the magnetization curve, M vs. H, for NbSe2 single crystals, in order to compare the superconducting (SC) state in the overdoped regime of La2−xSrxCuO4 (LSCO) with the SC state of the layered conventional superconductor NbSe2. While a plateau in χ vs. T in a moderate magnetic field and a so-called second peak in M vs. H, which is due to the marked enhancement of vortex pinning, have been observed in the overdoped regime of LSCO, these behaviors have not been observed in NbSe2. The present results indicate that the anomalously marked enhancement of vortex pinning is a characteristic feature in the overdoped LSCO where a microscopic phase separation into SC and normal-state regions takes place.

Our recent works on the synthesis of oxide superconductors using soft-chemical techniques are reviewed. First, Li-intercalation into layered perovskites has been carried out. We have found new Li-intercalated superconductors of the Ruddlesden-Popper phase of Li x Sr 2 CuO 2 X 2 (X = Br, I) with T c = 7–8 K and the Dion-Jacobson phase of Li x ASr 2 Nb 3 O 10 (A = Rb, Cs) with T c ∼6 K. However, no superconductivity has appeared in Aurivillius phases of Li x Bi 4 Ti 3 O 10 and Li x Bi 2 MO 6 (M = Mo, W). Next, we have succeeded in preparing insulating La 2 CuO 4 with the Nd 2 CuO 4 -type (T′) structure and superconducting Ba 0.6 K 0.4 BiO 3 by the direct precipitation from molten alkaline-metal hydroxides at a temperature as low as 260–350 °C.

Electron-doping into Nd 2 PdO 4 and Ba 2 PdO 2 F 2 with the same structure as in the electron-doped high- T c superconductor T′-Nd 2− x Ce x CuO 4 has been tried by introducing oxygen vacancies or intercalating Li + ions in order to bring about superconductivity. Polycrystalline samples of T′-Nd 2 PdO 4 were synthesized by the solid-state reaction method using a NaCl-flux technique. In order to introduce oxygen vacancies, the samples were annealed at 600–700 °C in flowing gas of argon or in vacuum. It has been found that the value of the electrical resistivity of T′-Nd 2 PdO 4− δ decreases down to ∼10 Ω cm through the annealing in vacuum, however, but it still remains semiconductive. Polycrystalline samples of T′-Ba 2 PdO 2 F 2 were prepared by the low-temperature fluorination of Ba 2 PdO 3 using ZnF 2 as a fluorinating agent. The intercalation of Li into T′-Ba 2 PdO 2 F 2 was tried using an electrochemical technique. However, it has been found from the ICP-AES analysis that Li + ions are not intercalated into T′-Ba 2 PdO 2 F 2 .

We use time- and angle-resolved photoemission to measure quasiparticle relaxation dynamics across a laser-induced superconducting phase transition in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$. Whereas low-fluence measurements reveal picosecond dynamics, sharp femtosecond dynamics emerge at higher fluence. Analyses of data as a function of energy, momentum, and doping indicate that the closure of the near-nodal gap and disruption of macroscopic coherence are primary mechanisms driving this onset. The results demonstrate the important influence of transient electronic structure on relaxation dynamics, which is relevant for developing an understanding of nonequilibrium phase transitions.

The superconducting critical temperature, $T_{\rm c}$, of FeSe can be dramatically enhanced by intercalation of a molecular spacer layer. Here we report on a $^{77}$Se, $^7$Li and $^1$H nuclear magnetic resonance (NMR) study of the powdered hyper-interlayer-expanded Li$_{x}($C$_2$H$_8$N$_2$)$_y$Fe$_{2-z}$Se$_2$ with a nearly optimal $T_{\rm c}=45$~K. The absence of any shift in the $^7$Li and $^1$H NMR spectra indicates a complete decoupling of interlayer units from the conduction electrons in FeSe layers, whereas nearly temperature-independent $^7$Li and $^1$H spin-lattice relaxation rates are consistent with the non-negligible concentration of Fe impurities present in the insulating interlayer space. On the other hand, strong temperature dependence of $^{77}$Se NMR shift and spin-lattice relaxation rate, $1/^{77}T_1$, is attributed to the hole-like bands close to the Fermi energy. $1/^{77}T_1$ shows no additional anisotropy that would account for the onset of electronic nematic order down to $T_{\rm c}$. Similarly, no enhancement in $1/^{77}T_1$ due to the spin fluctuations could be found in the normal state. Yet, a characteristic power-law dependence $1/^{77}T_1\propto T^{4.5}$ still comply with the Cooper pairing mediated by spin fluctuations., Comment: 7 pages, 6 figures

A new iron-based superconductor, Lix(C6H16N2)yFe2-zSe2, with Tc = 38 K has successfully been synthesized via the intercalation of lithium and hexamethylenediamine into FeSe. The superconducting transition has been confirmed not only by magnetic susceptibility measurements but also by electrical resistivity ones. The interlayer spacing, namely, the dicstance between neighboring Fe layers, d, is 16.225(5) $\mathring{\text{A}}$, which is the largest among those of FeSe-based intercalation compounds. It has been found that the dependence of Tc on d in FeSe-based intercalation superconductors appears domic., Comment: 10 pages, 5 figures