35 research outputs found
Interplay between Vortex Dynamics and Superconducting Gap Structure in Layered Organic Superconductors
No full textLayered organic superconductors motivate intense investigations because they provide various unexpected issues associated with their low dimensionality and the strong electron correlation. Since layered organic superconductors possess simple Fermi surface geometry and they often share similarities to the high temperature oxide superconductors and heavy fermion compounds, research on layered organic superconductors is suitable for understanding the essence and nature of strongly correlated electron systems. In strongly correlated electron systems, one of the central problems concerning the superconducting (SC) state is the symmetry of the SC gap, which is closely related to the paring mechanism. Thus, experimental determination of the SC gap structure is of essential importance. In this review, we present the experimental results for the in-plane angular variation of the flux-flow resistance in layered organic superconductors k-(ET)2Cu(NCS)2, β″-(ET)2SF5CH2CF2SO3, and λ-(BETS)2GaCl4. The interplay between the vortex dynamics and nodal structures is discussed for these superconductors
Electrodeposition of oxide-carbide composites of CrFeCoNiMo and measurement of catalytic activity on oxygen evolution reaction
No full textAbstract Many high-entropy oxides exhibit excellent catalytic activity in the oxygen evolution reaction for water splitting. In this study, a coating of oxide-carbide composites containing Cr, Fe, Co, Ni, and Mo was electrodeposited in a C2H6SO (DMSO)-based solution. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of carbides, oxides, and oxygen vacancies. Except for some metallic nickel, most metals exist in the oxidized or hydroxide states. Aqua- and chloro-complexes of metal ions have been proposed to form oxides and carbides on copper via the reduction of hydrated water and organic molecules. The coating exhibited high catalytic activity for the oxygen evolution reaction in an alkaline solution, achieving an overpotential of 216 mV, corresponding to a current density of 10 mA cm. The long-term stability at the current density of 10 mA cm−2 was investigated for 50 h, with a stable overpotential and minor surface dissolution. The catalytic activity was determined using density functional theory, and the unsaturated oxidation number of the metal atoms was calculated to depict the relationship between the binding state and the overpotential of the active sites. Graphical abstrac
Experimental assessment of quasi-binary picture of thermotropics: Induced smectic A phase in 7CB–n-heptane system
No full textjournal articl
Inhomogeneous superconducting state in hydrogen storage alloy PdDx
No full textapplication/pdfDisorder affects the coherent state of a superconductor in characteristic ways. In conventional superconductors with s-wave pairing symmetry, magnetic defects act as strong pair breakers, whereas nonmagnetic defects have negligible effect. In this review, we will show that nonmagnetic defects promote the superconductivity mediated by optical phonon in palladium-hydride system. Temperature dependence of the critical current is well fitted by the Ambegaokar-Baratoff relation, suggesting the existence of Josephson junction between the superconducting(SC) grains. Appearance of the coherent SC grains through the Josephson coupling may be associated with the interaction between deuterium and lattice defects such as vacancies and dislocations. In addition, we theoretically investigated whether or not optical phonon modes formed by the collective motion of a large number of atoms exist in nonstoichiometric PdHx, possessing random or inhomogeneous lattices. We found that individual excitations compete with collective excitations in controlling the system’s randomness, and that optical phonons develop from localized phonon modes as the stoichiometry x increases.departmental bulletin pape
Correlation between upper critical field and dimensionality in an unconventional superconductor
No full textapplication/pdfβ-(BDA-TTP)2SbF6 is a layered organic superconductor with relatively high transition temperature Tc of 7.5 K. In order to investigate the superconducting(SC) state of β-(BDA-TTP)2SbF6, its interlayer resistance has been measured at magnetic fields up to 15 T and temperatures down to 1.5 K. The upper critical fields(Hc2) parallel and perpendicular to the conduction layer are determined and dimensional crossover from anisotropic three-dimensional(3D) behavior to 2D behavior is found around 6 K. When a magnetic field is rotated within the conduction layer at 6 K, Hc2 for magnetic field along the a* + c* direction is slightly larger than that for along the a* - c* direction. Normal-state magnetoresistance has the same symmetry as Hc2 and shows maximum(minimum) when a magnetic field is applied parallel to the a* - c*(a* + c*) direction. This behavior can be explained in terms of a Fermi surface anisotropy. At 3.5 K, however, we find clear fourfold symmetry of Hc2 despite the normal-state magnetoresistance shows twofold symmetry arising from the Fermi surface anisotropy. Origin of fourfold symmetry of Hc2 is discussed in terms of SC gap structure in β-(BDA-TTP)2SbF6.departmental bulletin pape
Interplay between vortex dynamics and superconducting gap structure in quasi-two-dimensional organic superconductors
No full textapplication/pdfOver the past three decades, unconventional superconductivity with anisotropic gap structure has been found in strongly correlated electron systems such as heavy fermion compounds, high Tc cuprates, and organic conductors. Unconventional superconductivity is characterized by anisotropic superconducting gap, which may have zeros (nodes) along certain directions in the Brillouin zone. The nodal structure is closely related to the pairing interaction, and it is widely believed that the presence of nodes is a signature of magnetic or some other exotic, rather than conventional phonon mediated, pairing mechanism. Thus, experimental determination of the gap function is of fundamental importance. However, the detailed gap structure is an unresolved issue for many unconventional superconductors. In this context, we have demonstrated for layered organic superconductors that flux-flow resistance under a magnetic field rotated within conducting layers provide a clue for determining the nodal directions. Here we present the experimental results for the angular variation of the flux-flow resistance in d-wave organic superconductors β”-(ET)2SF5CH2CF2SO3 and λ-(BETS)2GaCl4. Nodal structures for these superconductors are briefly discussed.departmental bulletin pape
A demonstration of visualizing sound waves by utilizing Lissajous curves
No full textapplication/pdfAn attractive demonstration, observation of chaotic Lissajous curves originating from sound
waves, was presented for the general public. A simple experimental setup used in this demonstration
consists of an optical lever, a rotating mirror, and a laser beam source. This system can detect a
variety of Lissajous patterns without an oscilloscope. Thus, this system can be regarded as a budget
oscilloscope. The application to program-based learning in physics education is briefly discussed.departmental bulletin pape
Negative thermal expansion emerging upon structural phase transition in ZrV2O7 and HfV2O7
No full textPolarization reversal by intramolecular disordering in organic ferroelectrics: trichloroacetamide
No full textStructural Analysis of Im3m Phase of BABH-n by Maximum Entropy Method(Poster session 1, New Frontiers in Colloidal Physics : A Bridge between Micro- and Macroscopic Concepts in Soft Matter)
No full textこの論文は国立情報学研究所の電子図書館事業により電子化されました。BABH-nは剛直なコアとその両側にアルキル鎖をもち,鎖長に応じて異なる対称性のキュービック液晶相(Ia3d相,Im3m相)を発現する.Ia3d相の内部構造は小角X線散乱の散乱強度の鎖長依存性を利用して決定されたが,Im3m相では同じ手法による構造決定はできない.本研究では,少数のピークから最も確からしい電子密度分布を推定する最大エントロピー法をIm3m相に適用した
