Search

Single crystals of Cs-intercalated NbS2 (Cs x NbS2) were synthesized using a CsCl/KCl self-flux. The size and Cs content of Cs x NbS2 single crystals increased upon adding Cd metal into the starting materials. When 10–30 at% of Cd per Nb was provided in the starting materials, plate-like Cs x NbS2 (x ∼ 0.3) single crystals with 1–2 mm in size and 10–100 μm in thickness were obtained. The superconducting transition temperature of these Cs x NbS2 single crystals was 1.65 K.

Superconducting quantum interference devices (SQUIDs) are magnetometers with ultra-high sensitivity that have garnered attention owing to their potential application in flux qubits for quantum computing. The Josephson junction is an important component that determines the characteristics of a SQUID. Based on the superconductivity of heavily boron-doped diamond (111) homoepitaxial layers with a high critical temperature (Tc > 10 K), we propose two types of Josephson junction structures with discontinuous (111) boundaries. These structures allow the SQUID to operate above liquid helium temperature (4.2 K) with high reproducibility. We analyzed local misorientation and strain (i.e., compressive, tensile, and shear strain) at the boundary via electron backscatter diffraction. The Josephson junction characteristics were attributed to the weak link with discontinuous boundaries of diamond (111) sectors.

Layered transition metal chalcogenides (Zr,Hf)GeTe4 were screened from the AtomWork database as potential pressure-induced superconductors by having a narrow bandgap and high density of states near...

Three growth methods were tested for producing high-transition temperature superconducting Bi$_2$Sr$_2$Ca$_{n-1}$Cu$_n$O$_{2n+4+{\delta}}$ whiskers, employing different ways to focus a compressive stress and size effect of the precursors. First, thermographic imaging was used to investigate thermal stress from temperature distribution in the precursors during growth annealing. To enhance thermal stress in the precursors, a thermal cycling method and an Ag-paste coating method were proposed and found to significantly accelerate the whisker growth. The use of pulverized precursors also promoted whisker growth, possibly due to contribution from the vapor-liquid-solid growth mechanism. The obtained whiskers revealed the typical composition, diffraction patterns, and superconducting properties of the Bi-2212 phase. The proposed methods were able to stably produce longer whiskers compared to the conventional method. Using the obtained whiskers, electrical transport measurements under high pressure were successfully performed at up to around 50 GPa.

A high-throughput first-principles calculation-assisted data-driven approach based on an inorganic materials database named AtomWork was performed to explore new superconducting materials. Specific band structures of a small band gap and flat band at band edges were used in a screening procedure. Among the candidates studied, we focused on AgIn5Se8, which shows a high density of state at the Fermi level. Single crystals of AgIn5Se8 were successfully obtained via a melt and slow cooling method. The valence states in AgIn5Se8 were estimated to be Ag1+, In3+, and Se2- using X-ray photoelectron spectroscopy. An electrical transport property of resistance was measured under high pressure using an electrodes-inserted diamond anvil cell. The sample exhibited an insulator-to-metal transition with a drastic decrease of the resistance by increasing the pressure up to 24.8 GPa. A possibility of a pressure-driven phase transition below this pressure was indicated by an enthalpy calculation. At a higher pressure region of 52.5 GPa, a pressure-induced superconducting transition was observed at 3.4 K. The maximum transition temperature was increased up to 3.7 K under the pressure of 74.0 GPa.

Data-driven exploration for pressure-induced superconductors was performed based on the high-throughput first-principles screening of electronic band structures. In the screening conditions, we foc...

Superconducting Sm(O,F)BiS2 single crystals were successfully grown using KI-KCl flux. The obtained single crystals were flat-shaped and their size was 500um. The structure and composition of the obtained single crystals were obtained using X-ray diffraction and X-ray spectroscopy. The lattice constants of the obtained Sm(O,F)BiS2 single crystals were evaluated to be a = 3.9672(4) A and c = 13.417(6) A, while their F/(O + F) molar ratio was approximately 0.17. The superconducting transition temperature of the obtained Sm(O,F)BiS2 single crystals was 4.8 K. This was different from the reported Sm(O,F)BiS2 with no superconducting transition above 2 K. The superconducting anisotropies of the upper critical field and effective mass model of the obtained Sm(O,F)BiS2 single crystals were estimated to be approximately 26 and 10, respectively., 22 pages, 7 figures

PrOBiS2 single crystals were successfully grown using a KCl flux. The obtained crystals had a plate-like shape with a typical size of 0.5-1.0 mm and well-developed ab-plane. The Pr valence of the grown crystals, as determined by an X-ray absorption fine structure spectroscopy analysis, was almost trivalent. The PrOBiS2 single crystals did not exhibit superconductivity down to 0.25 K. The transport properties under high pressures up to 50 GPa ensured semiconducting behavior for 2-300 K using a diamond anvil cell., 19 pages, 5 figures

The high-pressure phase of La(O,F)BiS2 exhibits the highest transition temperature among all the BiS2-based superconductors. Various studies, such as the investigation of isotope effects, have been conducted to explain its superconducting mechanism. However, there are very few reports on the electrical transport properties and vibration modes of single-crystalline La(O,F)BiS2 under high pressure. In this study, we developed a diamond anvil cell with dual-probe diamond electrodes to measure the electrical transport properties of La(O,F)BiS2 single crystal and Pb as a manometer at low temperature. Using the developed system, a linear decrease in the transition temperature and phonon hardening was observed under the application of pressure on La(O,F)BiS2 single crystal.

We demonstrate nano- and micro-size patterning processes for high quality single crystal superconducting boron-doped diamond films with low damage using selective microwave plasma chemical vapour deposition and selective oxygen plasma etching. The offset critical temperature Tc(offset) of the micro strip is 10.2 K even if the strip width is 1 μm. However, we show that the critical temperature at zero resistivity Tc(zero) of several narrow strips is decreased owing to the unexpected defects induced by polishing damage and natural nanoscale scratch injury. These defects will induce a two-step superconducting transition. The probability of this tendency increases with decreasing the strip width. We also reveal that the critical current density Jc increases with decreasing the strip width, especially below 30 μm. By using a transport measurement, the maximum Jc is estimated to be 917,000 A/cm2 at 2.0 K with a strip width of 2 μm, which is the highest value reported for a superconducting diamond film. The upper critical field is estimated to be 11.5 T by the WHH approximation and 9.3 T by BCS fitting. Such high values mean superconducting diamond wiring can be used under a high magnetic field. We also attempt to fabricate nano-patterning and reveal that the transition temperature suddenly decreases below 400 nm, and superconductivity is not observed below 300 nm. This work contributes to the future development of superconducting nano- and micro-electro mechanical systems by exploiting the excellent properties of robustness, processability, high transition temperature, critical current density, and critical field associated with diamond.

It is now well established that the microstructure of Fe-based chalcogenide K x Fe2−ySe2 consists of, at least, a minor (~15 percent), nano-sized, superconducting K s Fe2Se2 phase and a major (~85 percent) insulating antiferromagnetic K2Fe4Se5 matrix. Other intercalated A1−xFe2−ySe2 (A = Li, Na, Ba, Sr, Ca, Yb, Eu, ammonia, amide, pyridine, ethylenediamine etc.) manifest a similar microstructure. On subjecting each of these systems to a varying control parameter (e.g. heat treatment, concentration x,y, or pressure p), one obtains an exotic normal-state and superconducting phase diagram. With the objective of rationalizing the properties of such a diagram, we envisage a system consisting of nanosized superconducting granules which are embedded within an insulating continuum. Then, based on the standard granular superconductor model, an induced variation in size, distribution, separation and Fe-content of the superconducting granules can be expressed in terms of model parameters (e.g. tunneling conductance, g, Coulomb charging energy, E c , superconducting gap of single granule, Δ, and Josephson energy J = πΔg/2). We show, with illustration from experiments, that this granular scenario explains satisfactorily the evolution of normal-state and superconducting properties (best visualized on a $${\boldsymbol{g}}{\boldsymbol{-}}\frac{{{\boldsymbol{E}}}_{{\boldsymbol{c}}}}{{\boldsymbol{\Delta }}}{\boldsymbol{-}}{\boldsymbol{T}}$$ g − E c Δ − T phase diagram) of A x Fe2−ySe2 when any of x, y, p, or heat treatment is varied.

Ce1–xPrxOBiS2 powders and Ce0.5Pr0.5OBiS2 single crystals were synthesized and their structure and superconductive properties were examined by X-ray diffraction, X-ray absorption, electronic resistivity, and magnetization. While PrOBiS2 was found to be in a monoclinic phase with one-dimensional Bi–S zigzag chains showing no superconductive transition above 0.1 K, CeOBiS2 was in a tetragonal phase with two-dimensional Bi–S planes showing zero resistivity below 1.3 K. In the range x = 0.3–0.9 in Ce1–xPrxOBiS2, both monoclinic and tetragonal phases were formed together with zero resistivity up to a maximum temperature of 2.2 K. A Ce0.5Pr0.5OBiS2 single crystal, which showed both zero resistivity and a decrease in magnetization at ∼2.4 K, presented a tetragonal structure. Short Bi–S bonding in flat two-dimensional Bi–S planes and mixed Ce3+/Ce4+ were characteristic features of the Ce0.5Pr0.5OBiS2 single crystal, which presumably triggered its superconductivity.

"F-free" CeOBiS$_2$ single crystals have successfully grown, thoroughly eliminating a concern about F-contamination by using a high-purity CsCl flux. The obtained crystals have a plate-like shape with a size of 1.0-3.0 mm in the well-developed plane. Single crystal X-ray structural analysis clearly revealed that the CeOBiS$_2$ crystallizes with a space group $P4/nmm$ (with lattice parameters of $a$ = 4.0189(6) {\AA}, $c$ = 13.573(2) {\AA}). The bond valence sum estimation and X-ray photoelectron spectroscopy analysis showed that the chemical state of Ce was in the mixed valence of Ce$^{3+}$ and Ce$^{4+}$. The single crystals show superconductivity with zero resistivity at $\sim$1.3 K. This is the first conclusive evidence of superconductivity driven by Ce valence fluctuation in surely non-doped CeOBiS$_2$. The superconducting transition temperature was enhanced up to $\sim$3.8 K by applying hydrostatic pressure., Comment: 27 pages, 8 figures, J. Alloys and Compd. (2017)

We have developed an approach to control the carrier density in various material under high pressure by the combination of an electric double layer transistor (EDLT) with a diamond anvil cell (DAC). In this study, this EDLT-DAC was applied to a Bi thin film, and here we report the field-effect under high pressure in the material. Our EDLT-DAC is a promising device for exploring unknown physical phenomena such as high transition-temperature superconductivity (HTS)., 10 pages, 4 figures

Physical review / B 101(2), 020508 (2020). doi:10.1103/PhysRevB.101.020508, The coexistence of phases, characterized by different electronic degrees of freedom, commonly occurs in layered superconductors. Among them, alkaline intercalated chalcogenides are model systems showing the microscale coexistence of paramagnetic (PAR) and antiferromagnetic (AFM) phases, however, the temporal behavior of different phases is still unknown. Here, we report a visualization of the atomic motion in the granular phase of KxFe2−ySe2 using x-ray photon correlation spectroscopy. Unlike the PAR phase, the AFM texture reveals an intermittent dynamics with avalanches as in martensites. When cooled down across the superconducting transition temperature Tc, the AFM phase goes through an anomalous slowing behavior, suggesting a direct relationship between the atomic motions in the AFM phase and the superconductivity. In addition to providing compelling evidence of avalanchelike dynamics in a layered superconductor, the results provide a basis for different theoretical models to describe the quantum states in inhomogeneous solids., Published by Inst., Woodbury, NY

NbBiCh$_3$ (Ch = S, Se) misfit-layered superconducting single crystals were successfully grown using a CsCl/KCl flux for the first time. The obtained crystals had a well-developed habit parallel to the c-plane with a typical width of 1-2 mm and thickness of 10-40 um. The superconducting transition temperatures with zero resistivity of NbBiS$_3$ single crystals obtained from the nominal composition of Nb0.9Bi1.2S3 was 0.31 K, and that value of the NbBiSe$_3$ single crystals grown from the stoichiometry composition (NbBiSe$_3$) was 2.3 K. Sharp decreases in electric resistivity and magnetic susceptibility at approximately 3 K suggested a possible superconducting transition temperature of NbBiSe$_3$. The normal-state anisotropy values of grown NbBiS$_3$ and NbBiSe$_3$ single crystals were 2.2-2.4 and 1.5-1.6, respectively., Comment: 4 figures + 3 figures (Supplementary Materials)

The effects of pressure on the superconducting properties of a Bi-based layered superconductor La2O2Bi3Ag0.6Sn0.4S6, which possesses a four-layer-type conducting layer, have been studied through the electrical resistance and magnetic susceptibility measurements. The crystal structure under pressure was examined using synchrotron X-ray diffraction at SPring-8. In the low-pressure regime, bulk superconductivity with a transition temperature Tc of ~ 4.5 K was induced by pressure, which was achieved by in-plane chemical pressure effect owing to the compression of the tetragonal structure. In the high-pressure regime above 6.4 GPa, a structural symmetry lowering was observed, and superconducting transitions with a Tc ~ 8 K were observed. Our results suggest the possible commonality on the factor essential for Tc in Bi-based superconductors with two-layer-type and four-layer-type conducting layers., Comment: 20 pages, 9 figures, supplemental materials

Polycrystalline samples of layered pnictogen (Pn) diselenide $\mathrm{Nd}{\mathrm{O}}_{0.8}{\mathrm{F}}_{0.2}\mathrm{S}{{\mathrm{b}}_{1}}_{\ensuremath{-}x}\mathrm{B}{\mathrm{i}}_{x}\mathrm{S}{\mathrm{e}}_{2}(x=0\phantom{\rule{0.16em}{0ex}}\mathrm{to}\phantom{\rule{0.16em}{0ex}}0.8)$ were successfully synthesized by solid-state reactions. Electrical resistivity in the synthesized samples systematically decreases with an increase in Bi content $x$, accompanied by an insulator to metal-like transition at $x=0.5\ensuremath{-}0.6$. Crystal structure analysis using synchrotron x-ray diffraction suggests that this transition correlates with anomalous change in $c$-axis length and/or distortion in Pn\ensuremath{-}Se conducting plane. Emergence of pressure-induced superconductivity was investigated using a diamond anvil cell with boron-doped diamond electrodes, employing $x=0.3$ and 0.7 as the representative samples. For the Sb-rich one $(x=0.3)$, we observed a signature of superconducting transition with ${{T}_{c}}^{\mathrm{onset}}=5.15\ifmmode\pm\else\textpm\fi{}0.05\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at 50 GPa. The ${{T}_{c}}^{\mathrm{onset}}$ of $x=0.3$ increased with increasing pressure and reached 7.65 \ifmmode\pm\else\textpm\fi{} 0.05 K at 70.8 GPa, followed by the gradual decrease in ${T}_{c}$ up to 90 GPa. For the Bi-rich one $(x=0.7)$, a superconducting transition with ${{T}_{c}}^{\mathrm{onset}}=5.5\ifmmode\pm\else\textpm\fi{}0.6\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ was induced at 43.5 GPa, which is almost comparable to that of $x=0.3$; besides, upper critical field $({H}_{c2})$ is evaluated to be $\ensuremath{\sim}10$ T for $x=0.7$, which is higher than that of $x=0.3\phantom{\rule{4pt}{0ex}}({H}_{c2}=6.7$ T at 50 GPa).

A direct patterning technique of gallium-irradiated superconducting silicon has been established by a focused gallium-ion beam without any mask-based lithography process. The electrical transport measurements for line- and square-shaped patterns of gallium-irradiated silicon were carried out under self-field and magnetic field up to 7 T. Sharp superconducting transitions were observed in both patterns at a temperature of 7 K. The line pattern exhibited a signature of higher onset temperature at around 12 K. A critical dose amount to obtain the superconducting gallium-irradiated silicon was investigated by the fabrication of various samples with different doses. This technique can be used as a simple fabrication method for a superconducting device.

(La,Ce)OBiS2 single crystals are successfully grown using CsCl flux. The obtained single crystals have a plate-like shape with a size of 0.5-2.0 mm and a well-developed ab-plane. The thickness of the crystals increases with a decrease in the Ce content. The (La,Ce)OBiS2 single crystals exhibit superconducting properties. Moreover, the superconducting transition temperature increases with an increase in the Ce content. The obtained (La,Ce)OBiS2 single crystals exhibit a tetragonal structure and the valence state of Ce in the crystals is determined to be mixed with Ce3+ and Ce4+ based on X-ray absorption fine structure spectroscopy., 12 pages, 6 figures

Temperature and pressure are essential parameters in the synthesis, evaluation, and application of functional materials. This study proposes the addition of a heating function to a high-pressure diamond anvil cell (DAC) with in-situ measurement probes. The proposed DAC allows for simultaneous control of temperature and pressure within the sample space and can be used to synthesize functional materials under extreme conditions. The various components, namely the heater, thermometer, and measurement probes, were fabricated with a boron-doped diamond epitaxial film and could be used repeatedly. The developed DAC was used to successfully conduct the high-pressure annealing of La(O,F)BiS$_{2}$ single crystal and the high-pressure synthesis of EuFBiS$_{2}$ superconductors. The proposed technique shows promise for further exploration of superconductors to broaden the research field.

Layered ternary transition-metal chalcogenides have been focused as a vein of exploration for superconductors. In this study, TiGeTe6 single crystals were synthesized and characterized by structural and valence state analyses and electrical transport measurements. The transport properties were measured under various pressures up to 71 GPa. The activation energy gets smaller as the applied pressure increases, and a signature of a pressure-induced metallization was observed under around 8.4 GPa. Under 13 GPa, pressure-induced superconductivity was discovered in this compound for the first time, with successive drops at 3 K and 6 K in the resistance, indicating the presence of multiple superconducting transitions. The superconducting transition temperature kept increasing as we further applied the pressure to the TiGeTe6 single crystal in the performed pressure range, reaching as high as 8.1 K under 71 GPa.

A novel superconductor, LaPt5As, which exhibits a new crystal structure was discovered by high-pressure synthesis using a Kawai-type apparatus. A superconducting transition temperature was observed at 2.6 K. Depending on the sintering pressure, LaPt5As has superconducting and non-superconducting phases with different crystal structures. A sintering pressure of around 10 GPa is effective to form single-phase superconducting LaPt5As. This material has a very unique crystal structure with an extremely long c lattice parameter of over 60 Å and corner-sharing tetrahedrons composed of network-like Pt layers. Density functional theory calculations have suggested that the superconducting current flows through these Pt layers. Also, this unique layered structure characteristic of LaPt5As is thought to play a key role in the emergence of superconductivity. Furthermore, due to a stacking structure which makes up layers, various structural modifications for the LaPt5As family are conceivable. Since such a high-pressure synthesis using a Kawai-type apparatus is not common in the field of materials science, there is large room for further exploration of unknown phases which are induced by high pressure in various materials.

This study demonstrated the oxygen deficiency (δ) dependence of the effect of applied pressure (Pappl) on the superconducting critical temperature (Tc) for a perovskite-related mixed-anion layered ...

A diamond anvil cell (DAC) has become an effective tool for investigating physical phenomena that occur at extremely high pressure, such as high-transition temperature superconductivity. Electrical transport measurements, which are used to characterize one of the most important properties of superconducting materials, are difficult to perform using conventional DACs. The available sample space in conventional DACs is very small and there is an added risk of electrode deformation under extreme operating conditions. To overcome these limitations, we herein report the fabrication of a boron-doped diamond microelectrode and undoped diamond insulation on a beveled culet surface of a diamond anvil. Using the newly developed DAC, we have performed in-situ electrical transport measurements on sulfur hydride H2S, which is a well-known precursor of the pressure-induced, high-transition temperature superconducting sulfur hydride, H3S. These measurements conducted under high pressures up to 192 GPa, indicated the presence of a multi-step superconducting transition, which we have attributed to elemental sulfur and possibly HS2.

Tin sulfide (SnS) single crystals were synthesized using a melt and slow-cooling method. The obtained crystals were characterized by x-ray diffraction, energy-dispersive spectrometry, and by x-ray photoelectron spectroscopy. Electrical transport properties of SnS were investigated under high pressure using a diamond anvil cell with boron-doped metallic diamond electrodes and an undoped diamond insulating layer. We successfully observed an insulator to metal transition between 8.1 and 12.5 GPa and pressure-induced superconductivity with a transition temperature (${T}_{c}$) of 5.8 K under 47.8 GPa as predicted by theoretical calculations. Comparing with the pressure-induced superconductivity in related SnSe compound, a possible ${T}_{c}$ enhancement in SnS by an increase of density of states at the Fermi level is expected.

We have successfully synthesized the c-axis oriented YBa2Cu4O8 (Y-124) film on a SrTiO3 (1 0 0) substrate via a coprecipitation and a dip-coating method. The precipitations including Y, Ba and Cu ions were obtained using their metal nitrates solution and the aqueous solution of sodium hydroxide and oxalic acid. Superconducting transition of the synthesized film was observed at 64-70 K corresponding to bulk Y-124 in the magnetization and resistance measurement. The developed method is suitable to synthesize superconducting Y-124 films for technological applications., Comment: 7 pages, 6 figures

A nematic transition preceding a long-range spin density wave antiferromagnetic phase is a common feature of many parent compounds of Fe-based superconductors. However, in the FeSe system with a nematic transition at ${T}_{\mathrm{s}}\ensuremath{\approx}90$ K, no evidence for long-range static magnetism is found down to very low temperatures. The lack of magnetism is a challenge for the theoretical description of FeSe. We investigated high-quality single crystals of FeSe using high-field (up to 9.5 T) muon spin rotation ($\ensuremath{\mu}\mathrm{SR}$) measurements. The $\ensuremath{\mu}\mathrm{SR}$ Knight shift and the bulk susceptibility linearly scale at high temperatures but deviate from this behavior around ${T}^{*}\ensuremath{\sim}10--20$ K, where the Knight shift exhibits a kink. In the temperature range ${T}_{\mathrm{s}}\ensuremath{\gtrsim}T\ensuremath{\gtrsim}{T}^{*}$, the muon spin depolarization rate shows a quantum critical behavior $\mathrm{\ensuremath{\Lambda}}\ensuremath{\propto}{T}^{\ensuremath{-}0.4}$. The observed critical scaling indicates that FeSe is in the vicinity of an itinerant antiferromagnetic quantum critical point. Below ${T}^{*}$ the quantum critical behavior breaks down. We argue that this breakdown is caused by a temperature-induced Lifschitz transition.

To observe the difference of atomic heights between the Se and Te layers with respect to the Fe layer in FeSe0.4Te0.6 single crystal, a Fe Kα fluorescence X-ray holography (XFH) experiment was performed at room temperature. The crystal structure of superconductor FeSe0.4Te0.6 obtained by X-ray diffraction (XRD) at a low temperature has distinct z-coordinates of Se and Te, remarkably different from each other. The reconstructed atomic image around central Fe atoms by XFH, however, reveals the different and complex results.

Candidates for new thermoelectric and superconducting materials, which have narrow band gap and flat bands near band edges, were searched by the high-throughput first-principles calculation from an inorganic materials database. The synthesized SnBi$_2$Se$_4$ among the target compounds showed a narrow band gap of 354 meV, and a thermal conductivity of 1 W/Km at ambient pressure. The sample SnBi$_2$Se$_4$ showed a metal-insulator transition at 11.1 GPa, as predicted by a theoretical estimation. Furthermore, the two pressure-induced superconducting transitions were discovered at under 20.2 GPa and 47.3 GPa. The data-driven search is a promising approach to discover new functional materials.

We report the pressure effect in Bi2Sr2Ca2Cu3O10+{\delta} (Bi-2223) single crystal with a small amount of intergrowth of Bi2Sr2CaCu2O8+{\delta} (Bi-2212). Their superconducting transition temperatures Tcs showed a domelike shape as a function of pressure, which showed a good agreement with the general relation between the carrier concentration and Tc. Our experimental results indicate that high pressure can induce effective carrier doping into the multilayered high-Tc cuprate superconductor, Comment: 8 pages including 5 figures

Sulfur-doped SnSe single crystal was successfully synthesized using a melt and slow-cooling method. The chemical composition and valence state of the obtained sample were analyzed by X-ray photoelectron spectroscopy. The pressure range of a diamond anvil cell with boron-doped diamond electrodes was upgraded to 104 GPa using nano-polycrystalline diamond anvil to investigate a pressure effect for the sample. Electrical resistivity measurements of sulfur-doped SnSe single crystal showed the insulator-metal-superconductor transition by applying high pressure up to 75.9 GPa.

Antimony (Sb) substitution of less than 8% was examined on a single crystal of a layered superconductor NdO0.7F0.3BiS2. The superconducting transition temperature of the substituted samples decreased as Sb concentration increased. A lattice constant along the c-axis showed a large decrease compared with that along the a-axis. Since in-plane chemical pressure monotonically decreased as Sb concentration increased, the suppression of the superconductivity is attributed to the decrease in the in-plane chemical pressure.

Superconducting FeSe films were electrochemically deposited on rolling-assisted biaxially textured substrate (RABiTS) tape. We observed zero resistivity in the as-electrodeposited FeSe film prepared on the RABiTS when the appropriate voltage was applied while it was dipped into the solution. When the RABiTS tape was dipped in the solution without applying voltage, a thin Se film was deposited on the substrate. The compositional ratio of the FeSe film got closer to the stoichiometric ratio with decreasing the dipping time before applying voltage.

Cd-doped La(O,F)BiS2 single crystals were grown using a CsCl/KCl flux. The grown crystals have a plate-like shape with ~1-2 mm square size in a well-developed ab-plane. The Cd doping in the crystals was successfully characterized by single crystal X-ray diffraction and electron probe microanalysis techniques. The superconductivity of La(O,F)BiS2 was gradually suppressed with Cd doping. The superconducting transition temperature with zero resistivity of La(O0.54F0.46)(Bi0.92Cd0.08)S2 was 2.3 K. The Cd doping does not change the superconducting anisotropy so much, albeit the considerable suppression of Tc., In Press, Solid State Communications 2017

We investigate the superconducting-gap anisotropy in one of the recently discovered BiS_{2}-based superconductors, NdO_{0.71}F_{0.29}BiS_{2} (T_{c}∼5 K), using laser-based angle-resolved photoemission spectroscopy. Whereas the previously discovered high-T_{c} superconductors such as copper oxides and iron-based superconductors, which are believed to have unconventional superconducting mechanisms, have 3d electrons in their conduction bands, the conduction band of BiS_{2}-based superconductors mainly consists of Bi 6p electrons, and, hence, the conventional superconducting mechanism might be expected. Contrary to this expectation, we observe a strongly anisotropic superconducting gap. This result strongly suggests that the pairing mechanism for NdO_{0.71}F_{0.29}BiS_{2} is an unconventional one and we attribute the observed anisotropy to competitive or cooperative multiple paring interactions.

Here we firstly report the pressure-induced superconductivity in phase change materials SnSb2Te4. Single crystals of SnSb2Te4 were grown using a conventional melting-down method. The resistance under pressure was measured using an originally designed diamond anvil cell with boron-doped diamond electrodes. The temperature dependence of the resistance under different pressures has been measured up to 32.6 GPa. The superconducting transition of SnSb2Te4 appeared at 2.1 K ([Formula: see text]) under 8.1 GPa, which was further increased with applied pressure to a maximum onset transition temperature 7.4 K under 32.6 GPa.

CsBi4-x Pb x Te6 is synthesized and the superconductivity associated with the structural transition from Pb substitution is studied. Photoemission spectroscopy measurements are performed in order to elucidate the relationship between the electronic structure and the occurrence of the superconductivity. When Bi is substituted with Pb, an electron doping-like change in the electronic structure is directly observed which is contrary to the naive expectation of hole doping. This observation is consistent with band structure calculations and appears to be a unique characteristic of CsBi4-x Pb x Te6 because of the dissociation of Bi dimers upon Pb substitution. These results indicate that it may be possible to control the electron and hole doping via manipulating the Bi dimers through Pb substitution.

The crystal structures of Ce(O,F)BiS2 synthesized from starting materials with five different F contents were determined by single-crystal X-ray analysis. An increase in F content in the starting materials slightly increased F incorporation in the grown single crystals. The grown crystals with various F contents showed similar layered structures, but minor structural changes were observed with different conductive and magnetic properties. Crystals grown from higher F content were found to have a nearly flat Bi–S plane and elongated Ce–(O,F) bond, and showed superconductive transition below ∼3 K and spontaneous magnetization below ∼7 K. The calculated density of states based on this structural analysis predicted that hybridized Bi 6p–S 3p orbitals intersect the Fermi level and that Ce states are located near the Fermi level. The effect of structural change on superconductivity and long-range magnetic ordering has been discussed.

We have fabricated single core superconducting FeTe0.4Se0.6 tapes using a process based on a chemical phase transformation from hexagonal Fe(Te0.4Se0.6)1.4 (non-superconducting) to tetragonal FeTe0.4Se0.6 (superconducting) via an optimal supply of Fe from the Fe sheath by annealing. This process enhanced a packing density of wire core inside the sheath, due to an expansion of the lattice volume via the transformation from high-density hexagonal Fe(Te0.4Se0.6)1.4 to low-density tetragonal FeTe0.4Se0.6. An obvious correlation between annealing temperature (Ta) and phase transformation was observed. Transformation of tape cores from hexagonal to tetragonal were observed above 500 °C. Finally, the hexagonal phase completely transformed into the tetragonal phase by annealing at 600 °C. The obtained superconducting tape showed superconductivity below ∼13.5 K. The magnetic Jc value of 3.0 × 103 A/cm2 at 4.2 K was obtained for the sample prepared by annealing at 525 °C for 3 h followed by annealing at 200 °C for 2 h.

We report conductivity measurements for mackinawite at atmospheric pressure and up to values of 1.64 GPa. As far as the authors are aware, this is the first low temperature transport measurements to be conducted on mackinawite. The sample shows semiconducting-like behaviour up to the maximum pressures applied but with a gradual flattening of the resistivity curve it is tentatively suggested that the system will undergo a semiconductor–metallic transition with a further application of pressure. Interestingly, this contradicts band structure and more recent density functional theory (DFT) calculations which predict a metallic system. However, the experimental data agrees with the original prediction of semiconducting behaviour made by Bertaut 1965. This research also shows that, at least in its parent form, mackinawite does not exhibit a superconductive state unlike its iso-structural counterpart tetragonal FeSe. This is also briefly discussed.