Synthesis and Superconductivity of New BiS2 Based Superconductor PrO0.5F0.5BiS2

We report synthesis and superconductivity at 3.7 K in PrO_0.5F_0.5BiS₂. The newly discovered material belongs to the layered sulfide based REO_0.5F_0.5BiS₂ compounds having a ZrCuSiAs-type structure. The bulk polycrystalline compound is synthesized by the vacuum encapsulation technique at 780 ^°C in a single step. Detailed structural analysis has shown that the as synthesized PrO_0.5F_0.5BiS₂ is crystallized in a tetragonal P4/nmm space group with lattice parameters a=4.015(5) Å, c=13.362(4) Å. Bulk superconductivity is observed in PrO_0.5F_0.5BiS₂ below 4 K from magnetic and transport measurements. Electrical transport measurements showed superconducting transition temperature (T _c ) onset at 3.7 K and T _c (ρ=0) at 3.1 K. The hump at T _c related to the superconducting transition is not observed in the heat capacity measurement and rather a Schottky-type anomaly is observed at below ～6 K. The compound is slightly semiconducting in a normal state. Isothermal magnetization (MH) exhibited typical type II behavior with a lower critical field (H _c1) of around 8 Oe.     

Effect of Cd Doping on Structure and Superconductivity in Mg0.5Cd0.5B2

The effect of Cd doping on structure and superconductivity in Mg_0.5Cd_0.5B₂ fabricated by a solid-state reaction at ambient pressure has been investigated. The resulting changes in crystal structure, superconducting transition temperature T _c and critical current density J _c are characterized by X-ray diffraction, dc magnetization, electrical resistance, and magnetic measurements. It reveals that Cd does not occupy the atomic Mg sites in the MgB₂ crystal structure, but merely reacts with Mg and forms a MgCd₃ phase. It is striking to note that although the nonsuperconducting phase MgCd₃ is as high as about 67 vol.% in Mg_0.5Cd_0.5B₂, the T _c of the doped sample drops only by about 1 K. Most important, a surprising improvement of J _c of 5.0 × 10⁵ A/cm² (5 K, 0 T) has been achieved in Mg_0.5Cd_0.5B₂. It is suggested that the improvement in J _c in Mg_0.5Cd_0.5B₂ is primarily due to pinning effects induced by MgCd₃. Also, it is thought that MgCd₃ may fill up gaps among grains in MgB₂ and produce better grain linkage, which may be another source of improvement in J _c in Mg_0.5Cd_0.5B₂.     

Thickness-Dependent Superconductivity in a Layered Electride on Silicon

Layered materials exhibit a plethora of fascinating properties. The challenge is to make the materials into epitaxial films, preferably integrated with mature technological platforms to facilitate their potential applications. Progress in this direction can establish the film thickness as a valuable parameter to control various phenomena, superconductivity in particular. Here, a synthetic route to epitaxial films of SrAlSi, a layered superconducting electride, on silicon is designed. A set of films ranging in thickness is synthesized employing a silicene-based template. Their structure and superconductivity are explored by a combination of techniques. Two regimes of T_C dependence on the film thickness are identified, the coherence length being the crossover parameter. The results can be extended to syntheses of other honeycomb-lattice ternary compounds on Si or Ge exhibiting superconducting, magnetic, and other properties.     

Superconductivity at 4 K in Pd-Deficient Layered Ta2Pd x S6

In the present short letter, we report on the low dimensional 4d and 5d transition metals-chalcogenide based compounds i.e., Ta2PdxS6, showing semiconducting to superconducting transition at around 4K with their upper critical fields outside the Pauli paramagnetic limit. It seems couple of different superconducting phases do exist in these new set of compounds. Our short letter in this regards is thought provoking, asking to explore various unearthed possible new superconducting phases in (Nb/Ta)2Pdx(S/Se/Te)y systems.     

Low-Energy Electronic Collective Modes and Superconductivity in Layered Systems

The Coulomb interaction induces low-energy electronic collective modes (LEECM) in layered conductors. We study how the superconducting critical temperature T _c is affected by such collective modes within the strong-coupling theory of superconductivity. Whereas we account for both the electron–phonon and the screened Coulomb interactions, the main focus is set on the latter. The dielectric function is displayed and screening within RPA is discussed. We then show that LEECM affect the superconducting state constructively in layered structures. Their effect can be interpreted as a negative * in the Eliashberg theory. We examine in what respect the collective-mode scenario differs in layered conductors as compared to three-dimensional (3D) isotropic metals.     

Dynamical Screening and Electron-Mediated Superconductivity in Intercalated Layered Metallochloronitrides

Metallochloronitrides are layered conductors that have recently been found to superconduct at critical temperatures up to T _c 26 K. It is known that the electron–phonon interaction is small in these systems, so that the conventional pairing mechanism through exchange of phonons is unable to provide for such high T _cs. We show that the dominant contribution to the pairing interaction in these materials comes from the exchange of low-energy collective modes, specific to layered conductors. The existence of such acoustic plasmons results from the incomplete screening of the Coulomb interaction perpendicular to the conducting planes which expresses itself in the dynamical nature of the screened Coulomb interaction.     

Magnetic Order and Superconductivity in Eu1.5Ce0.5RuSr2Cu2O10

AC magnetic susceptibility, (T), and do resistivity, (T), measurements have been performed to study the superconductivity and magnetic properties of a polycrystalline Eu_1.5Ce_0.5RuSr₂Cu₂O₁₀. X-ray diffraction shows that the single-phase compound crystallized into a tetragonal symmetry of space group I4/mmm. Ru spin ordering and superconductivity at 75 and 37 K, respectively, were evident in (T). The magnetic responses associated with the Ru spin ordering were found to be strongly reduced by a weak applied field, indicating an antiferromagnetic character for the Ru moments. A two-step transition to the superconducting state was observed in (T), where an intra-granular transition at T _C1=37 K and an inter-granular transition at T _C2=20 K were clearly seen. These observations confirm the coexistence of superconductivity and magnetic order at low temperatures.     

层状Li(Ni0.5Mn0.5)1-xTixO2材料的合成及性能研究

以Li2CO3,Ni(OH)2,MnCO3,TiO2为原料,采用高温固相合成法制备了层状Li(Ni0.5Mn0.5)1-xTixO2.通过X射线衍射确定了不同钛掺杂量样品的相组成.用扫描电镜对组织形貌进行了观测.对用所制样品组装的电池的充放电和循环性能进行了测试.实验结果得出:所制备的Li(Ni0.5Mn0.5)1-xTixO2的结构为α-NaFeO2型层状结构,当x=0.02时,Li(Ni0.5Mn0.5)1-xTixO2的首次放电容量为161 mA·h/g,25次循环后容量仍保持在144 mA·h/g,具有较高的比容量和良好的循环性.     

Superconductivity in Co and Li Substituted Cu0.5Tl0.5Ba2Ca2Cu3?x Co x O10?��

We have tried to explore the possible sources of suppression of superconducting properties in cobalt substituted Cu_0.5Tl_0.5Ba₂Ca₂Cu_3?x Co _x O_10??? (x=0,0.05,0.1,0.5) superconductor. It can be expected from these studies that Co substitution at Cu sites in the CuO₂ planes somehow localizes the carriers and decreases the mobile carriers density. The density of mobile carriers in the CuO₂ planes can be restored by partial substitution of Li at Tl sites in Cu_0.5Tl_0.5Ba₂O_4??? charge reservoir layer of Cu_0.5Tl_0.5Ba₂Ca₂Cu_3?x Co _x O_10??? superconductor; since alkali metals are known to lose their outermost ??s-orbital?? electron easily, which can be supplied to the CuO₂ planes. The post-annealing experiments on these samples have been carried out in flowing oxygen and nitrogen and the motivation behind these extreme post-annealing conditions was to optimize the carriers density in the CuO₂ planes of Cu_0.5Tl_0.5Ba₂Ca₂Cu_3?x Co _x O_10??? superconductor. The optimized free carrier density in the CuO₂ planes enhances the superconducting properties of the final compound.     

Acoustic Plasmons in Layered Systems and the Phonon-Plasmon Mechanism of Superconductivity

We address the question whether or not acoustic collective modes contribute to superconductivity in a layered electron gas. We calculate T _c within the strong-coupling phonon-plasmon scheme. The plasmon pairing kernel is calculated explicitly. We demonstrate that plasmons may contribute constructively to superconductivity. The result shows that one can interpret the effect of low-energy collective modes in terms of an effective negative *.     

Superconductivity in a new quaternary phase with HgSm0.5In0.5Pb2 composition

This work reports a systematic study on the structural and superconducting properties in the Hg-Sm-In-Pb system. It is investigated how In and Sm dopings influence the superconducting properties of the HgPb₂ phase which was recently reported. Results for the HgSm_1 − xPb₂ system show that Sm atoms substitute Hg vacancies in the tetragonal phase which do not affect the onset critical temperature of the HgPb₂ compound. Simultaneous Sm and In doping effects on the properties of the HgPb₂ phase are also studied. Experimental and simulations of X-ray powder diffractograms suggest that the HgSm_1 − xIn_xPb₂ system (0.2 ≤ x ≤ 0.7) has a pseudo-cubic structure with lattice parameters near 4.88 Å. Superconducting properties measurements show that this system has an optimum doping at x ∼ 0.5 with the onset critical temperature close to 6.9 K. This is the highest superconducting critical temperature for the AuCu prototype so far reported.     

Enhanced capacity for lithium–air batteries using LaFe0.5Mn0.5O3–CeO2 composite catalyst

LaFe_0.5Mn_0.5O₃ and Ce-incorporated LaFe_0.5Mn_0.5O₃ catalysts for Li–air batteries were synthesized by co-precipitation (CP) and micro-emulsion methods with the increasing Ce/(La+Ce) ratios from 0 to 0.5. Ce has a low solubility in LaFe_0.5Mn_0.5O₃ perovskite lattices. Instead of forming single-phase La_1?x Ce _x Fe_0.5Mn_0.5O₃ perovskite, a multi-phase LaFe_0.5Mn_0.5O₃–CeO₂ composite was obtained even for Ce/(La+Ce) = 0.05. Such catalysts were used in the cathode of Li–air batteries and the discharge test showed that LaFe_0.5Mn_0.5O₃–CeO₂ composite catalyst can effectively improve the specific capacity with the highest capacity of ~4700 mAh/g for Ce/(La+Ce) = 0.05 (by CP). There is also a 0.05 V increase in discharge voltage compared with the reference cell without catalyst, with the discharge voltage plateau at ~2.75 V. The overall ranking in terms of capacity was Ce/(La+Ce) = 0.05 > Ce/(La+Ce) = 0.1 > Ce/(La+Ce) = 0.5 > Ce/(La+Ce) = 0. The capacity increase for Ce/(La+Ce) = 0.05 and 0.1 samples is attributed to the enhanced oxygen storage/release capability and the increased conductivity with the incorporation of CeO₂.     

Effect of Cd Doping on Structure and Superconductivity in Mg0.5Cd0.5B2

The effect of Cd doping on structure and superconductivity in Mg_0.5Cd_0.5B₂ fabricated by a solid-state reaction at ambient pressure has been investigated. The resulting changes in crystal structure, superconducting transition temperature T _c and critical current density J _c are characterized by X-ray diffraction, dc magnetization, electrical resistance, and magnetic measurements. It reveals that Cd does not occupy the atomic Mg sites in the MgB₂ crystal structure, but merely reacts with Mg and forms a MgCd₃ phase. It is striking to note that although the nonsuperconducting phase MgCd₃ is as high as about 67 vol.% in Mg_0.5Cd_0.5B₂, the T _c of the doped sample drops only by about 1 K. Most important, a surprising improvement of J _c of 5.0 × 10⁵ A/cm² (5 K, 0 T) has been achieved in Mg_0.5Cd_0.5B₂. It is suggested that the improvement in J _c in Mg_0.5Cd_0.5B₂ is primarily due to pinning effects induced by MgCd₃. Also, it is thought that MgCd₃ may fill up gaps among grains in MgB₂ and produce better grain linkage, which may be another source of improvement in J _c in Mg_0.5Cd_0.5B₂.     

Appearance of Superconductivity at 15.9 K in Layered V<Subscript>2</Subscript>AlN

A bulk polycrystalline sample with the nominal compositions represented by V₂AlN_1?δ was synthesized by a two-step solid-state reaction. The structural characterization has been done via X-ray diffraction, followed by Rietveld refinements, which revealed that the layered V₂AlN is crystalized in cubic Fm3m space group with lattice parameters a = b = c = 6.127 Å. Both DC resistivity and magnetization measurements confirmed that V₂AlN is a bulk superconductor with superconducting transition temperature (T _c ) of 15.9 K.     

Field-Induced Superconductivity in MoS2

Semiconducting TMDs are nowadays attracting great interest after the invention of the so-called “Scotch-tape method” established in graphene research. Semiconducting TMDs are front-runners of “post graphene” materials for their finite band gap crucial for device applications. MoS₂ is the most widely used TMD because of its application as a solid lubricant. Scientifically, it shows superconductivity after alkali or alkaline-earth doping with a highest T _c of around 7 K. Recently, we succeeded in inducing superconductivity in the MoS₂ transistor adopting electric double layer (EDL), a nanosized capacitor, as a gate dielectric. The field-induced superconducting transition of MoS₂ was realized with a maximum T _c around 11 K, the highest not only within a reported MoS₂ compound, but also among TMDs. This highest T _c lies in the carrier density region much smaller than a chemically doped compound; a low density region has never been successfully accessed by chemical methods. Combining a HfO₂ (high-k) back gate, quasi-continuous control of carrier density, and thus quantum phase, was demonstrated to unveil the phase diagram; the T _c exhibits strong carrier density dependence with a superconducting dome. Our result implies a common existence of the superconducting dome in 2D band insulators.     

Investigation of Potassium Storage in Layered P3‐Type K0.5MnO2 Cathode

Novel and low‐cost batteries are of considerable interest for application in large‐scale energy storage systems, for which the cost per cycle becomes critical. Here, this study proposes K_0.5MnO₂ as a potential cathode material for K‐ion batteries as an alternative to Li technology. K_0.5MnO₂ has a P3‐type layered structure and delivers a reversible specific capacity of ≈100 mAh g^?1 with good capacity retention. In situ X‐ray diffraction analysis reveals that the material undergoes a reversible phase transition upon K extraction and insertion. In addition, first‐principles calculations indicate that this phase transition is driven by the relative phase stability of different oxygen stackings with respect to the K content.     

Probing the Superconducting Pairing Symmetry from Spin Excitations in BiS2 Based Superconductors

Starting from a two-orbital model and based on the random phase approximation, spin excitations in the superconducting state of the newly discovered BiS₂ superconductors with three possible pairing symmetries are studied theoretically. It is found that the spin response is uniquely determined by the pairing symmetry. Possible spin resonance excitations may occur at an incommensurate momentum about (0.7π,0.7π) for the d-wave symmetry, while the transverse spin excitation near (0,0) is enhanced for the p-wave symmetry and no spin resonance signature is seen for the s-wave pairing symmetry. These distinct features may be used for probing or determining the pairing symmetry in this newly discovered compound.