Single-crystal growth of the ternary BaFe2_2As2_2 phase using the vertical Bridgman technique

Ternary Ba-Fe-As system has been studied to determine a primary solidification field of the BaFe$_2$As$_2$ phase. We found that the BaFe$_2$As$_2$ phase most likely melts congruently and primarily solidifies either in the FeAs excess or Ba$_{x}$As$_{100-x}$ excess liquid. Knowing the primary solidification field, we have performed the vertical Bridgman growth using the starting liquid composition of Ba$_{15}$Fe$_{42.5}$As$_{42.5}$. Large single crystals of the typical size 10x4x2 mm$^3$ were obtained and their quality was confirmed by X-ray Laue and neutron diffraction.Comment: Submitted to Jpn. J. Appl. Phys.; revise

FABRICATION OF POROUS, CRYSTALLINE-ORIENTED TITANIA LAYER ON TRANSPARENT ELECTRODE BY MAGNETIC FIELD-ASSISTED EPD

Dye-sensitized solar cells (DSSCs) are the most extensively investigated systems for the conversion of solar energy into electricity, since it can convert light at longer wavelengths into electricity and can be manufactured using less energy compared to the bulk semiconductor-type cells with a p-n junction. Despite these advantages, DSSC commercialization is still limited because of its low conversion efficiency and low reliability of the liquid electrolyte. The low conversion efficiency is due to the non-uniformity of the electrode components with respect to the packing density of TiO2 particles and film thickness of the electrode. Therefore the research on DSSC in general has been directed toward improving the photo-current and photo-potential. In order to significantly enhance the cell performance, it is important to optimize the photo-anode structure of the DSSC on the basis of its fundamental properties. In this study, crystalline-oriented porous TiO2 thin films were fabricated on indium-tin oxide (ITO) or fluorine-doped tin oxide (FTO) glass substrates by electrophoretic deposition (EPD) in a superconducting magnet. Please click Additional Files below to see the full abstract

Peierls instability, periodic Bose-Einstein condensates and density waves in quasi-one-dimensional boson-fermion mixtures of atomic gases

We study the quasi-one-dimensional (Q1D) spin-polarized bose-fermi mixture of atomic gases at zero temperature. Bosonic excitation spectra are calculated in random phase approximation on the ground state with the uniform BEC, and the Peierls instabilities are shown to appear in bosonic collective excitation modes with wave-number $2k_F$ by the coupling between the Bogoliubov-phonon mode of bosonic atoms and the fermion particle-hole excitations. The ground-state properties are calculated in the variational method, and, corresponding to the Peierls instability, the state with a periodic BEC and fermionic density waves with the period $\pi/k_F$ are shown to have a lower energy than the uniform one. We also briefly discuss the Q1D system confined in a harmonic oscillator (HO) potential and derive the Peierls instability condition for it.Comment: 9 pages, 3figure

Low-momentum nucleon-nucleon interaction and its application to few-nucleon systems

Low-momentum nucleon-nucleon interactions are derived within the framework of a unitary-transformationtheory, starting with realistic nucleon-nucleon interactions. A cutoff momentum L is introduced to specify aborder between the low- and high-momentum spaces. By Faddeev-Yakubovsky calculations the lowmomentuminteractions are investigated with respect to the dependence of ground-state energies of 3H and 4Heon the parameter L. It is found that we need the momentum cutoff parameter Lù5 fm−1 in order to reproducesatisfactorily the exact values of the binding energies for 3H and 4He. The calculation with L=2 fm−1 recommendedby Bogner et al. leads to considerable overbinding at least for few-nucleon systems

Low-momentum nucleon-nucleon interaction and its application to few-nucleon systems

Low-momentum nucleon-nucleon interactions are derived within the framework of a unitary-transformation theory, starting with realistic nucleon-nucleon interactions. A cutoff momentum L is introduced to specify a border between the low- and high-momentum spaces. By Faddeev-Yakubovsky calculations the lowmomentum interactions are investigated with respect to the dependence of ground-state energies of 3H and 4He on the parameter L. It is found that we need the momentum cutoff parameter Lù5 fm−1 in order to reproduce satisfactorily the exact values of the binding energies for 3H and 4He. The calculation with L=2 fm−1 recommended by Bogner et al. leads to considerable overbinding at least for few-nucleon systems

Phase Diagram of Pressure-Induced Superconductivity in EuFe2As2 Probed by High-Pressure Resistivity up to 3.2 GPa

We have constructed a pressure$-$temperature ($P-T$) phase diagram of $P$-induced superconductivity in EuFe$_2$As$_2$ single crystals, via resistivity ($\rho$) measurements up to 3.2 GPa. As hydrostatic pressure is applied, an antiferromagnetic (AF) transition attributed to the FeAs layers at $T_\mathrm{0}$ shifts to lower temperatures, and the corresponding resistive anomaly becomes undetectable for $P$ $\ge$ 2.5 GPa. This suggests that the critical pressure $P_\mathrm{c}$ where $T_\mathrm{0}$ becomes zero is about 2.5 GPa. We have found that the AF order of the Eu$^{2+}$ moments survives up to 3.2 GPa without significant changes in the AF ordering temperature $T_\mathrm{N}$. The superconducting (SC) ground state with a sharp transition to zero resistivity at $T_\mathrm{c}$ $\sim$ 30 K, indicative of bulk superconductivity, emerges in a pressure range from $P_\mathrm{c}$ $\sim$ 2.5 GPa to $\sim$ 3.0 GPa. At pressures close to but outside the SC phase, the $\rho(T)$ curve shows a partial SC transition (i.e., zero resistivity is not attained) followed by a reentrant-like hump at approximately $T_\mathrm{N}$ with decreasing temperature. When nonhydrostatic pressure with a uniaxial-like strain component is applied using a solid pressure medium, the partial superconductivity is continuously observed in a wide pressure range from 1.1 GPa to 3.2 GPa.Comment: 7 pages, 6 figures, accepted for publication in Physical Review B, selected as "Editors' Suggestion