Migratory history of wild and released ayu (Plecoglossus altivelis) in the Kurobe River, Japan

In order to discuss the influence of dam discharge on the movement of ayu Plecoglossus altivelis in a river and the stocking effectiveness of released ayu, the migratory history of 83 juveniles of ayu (standard length=67.9-142.4mm sL) collected in the Kurobe River, Japan during 25 June-23 August 2004 was determined by otolith microchemistry, and the origin of fish was identified as being either native amphidromous ayu or released amphidromous or landlocked fish. Except for otoliths with abnormal morphology (N=10), most specimens (96%, N=70) had inner layers (radius:>400μm) of higher Sr: Ca ratios and outer ones of low values. These specimens were identified as native amphidromous fish that migrated upstream from the sea. Only 4% (N=3) were released ayu (reared fish), which were further divided into two origins, amphidromous fish (N=2) with smaller inner layers (radius:<400μm) of high Sr: Ca ratios, and landlocked fish (N=1) with constantly low values over the whole otolith. There were no specimens with an increase in Sr: Ca ratios in the outer layers of the low Sr: Ca region of the otolith after their upstream migration in spring, suggesting that it is unlikely that any of these ayu had been washed-out from the river by cold and turbulent river water

Electronic Structure, Magnetism and Superconductivity of Layered Iron Compounds

The layered iron superconductors are discussed using electronic structure calculations. The four families of compounds discovered so far, including Fe(Se,Te) have closely related electronic structures. The Fermi surface consists of disconnected hole and electron cylinders and additional hole sections that depend on the specific material. This places the materials in proximity to itinerant magnetism, both due to the high density of states and due to nesting. Comparison of density functional results and experiment provides strong evidence for itinerant spin fluctuations, which are discussed in relation to superconductivity. It is proposed that the intermediate phase between the structural transition and the SDW transition in the oxy-pnictides is a nematic phase.Comment: Proceedings ISS200

On the multi-orbital band structure and itinerant magnetism of iron-based superconductors

This paper explains the multi-orbital band structures and itinerant magnetism of the iron-pnictide and chalcogenides. We first describe the generic band structure of an isolated FeAs layer. Use of its Abelian glide-mirror group allows us to reduce the primitive cell to one FeAs unit. From density-functional theory, we generate the set of eight Fe $d$ and As $p$ localized Wannier functions for LaOFeAs and their tight-binding (TB) Hamiltonian, $h(k)$. We discuss the topology of the bands, i.e. allowed and avoided crossings, the origin of the d6 pseudogap, as well as the role of the As $p$ orbitals and the elongation of the FeAs$_{4}$ tetrahedron. We then couple the layers, mainly via interlayer hopping between As $p_{z}$ orbitals, and give the formalism for simple and body-centered tetragonal stackings. This allows us to explain the material-specific 3D band structures. Due to the high symmetry, several level inversions take place as functions of $k_{z}$ or pressure, resulting in linear band dispersions (Dirac cones). The underlying symmetry elements are, however, easily broken, so that the Dirac points are not protected, nor pinned to the Fermi level. From the paramagnetic TB Hamiltonian, we form the band structures for spin spirals with wavevector $q$ by coupling $h(k)$ and $h (k+q)$. The band structure for stripe order is studied as a function of the exchange potential, $\Delta$, using Stoner theory. Gapping of the Fermi surface (FS) for small $\Delta$ requires matching of FS dimensions (nesting) and $d$-orbital characters. The origin of the propeller-shaped FS is explained. Finally, we express the magnetic energy as the sum over band-structure energies, which enables us to understand to what extent the magnetic energies might be described by a Heisenberg Hamiltonian, and the interplay between the magnetic moment and the elongation of the FeAs4 tetrahedron

Importance of Itinerancy and Quantum Fluctuations for the Magnetism in Iron Pnictides

By applying density functional theory, we find strong evidence for an itinerant nature of magnetism in two families of iron pnictides. Furthermore, by employing dynamical mean field theory with continuous time quantum Monte Carlo as an impurity solver, we observe that the antiferromagnetic metal with small magnetic moment naturally arises out of coupling between unfrustrated and frustrated bands. Our results point to a possible scenario for magnetism in iron pnictides where magnetism originates from a strong instability at the momentum vector ($\pi$, $\pi$, $\pi$) while it is reduced by quantum fluctuations due to the coupling between weakly and strongly frustrated bands.Comment: 4 pages, 4 figure

Magnetic Properties of Ab initio Model for Iron-Based Superconductors LaFeAsO

By using variational Monte Carlo method, we examine an effective low-energy model for LaFeAsO derived from an ab initio downfolding scheme. We show that quantum and many-body fluctuations near a quantum critical point largely reduce the antiferromagnetic (AF) ordered moment and the model not only quantitatively reproduces the small ordered moment in LaFeAsO, but also explains the diverse dependence on LaFePO, BaFe2As2 and FeTe. We also find that LaFeAsO is under large orbital fluctuations, sandwiched by the AF Mott insulator and weakly correlated metals. The orbital fluctuations and Dirac-cone dispersion hold keys for the diverse magnetic properties.Comment: 4 pages, 4 figure

Odor Removal Characteristics of a Laminated Film-Electrode Packed-Bed Nonthermal Plasma Reactor

Odor control has gained importance for ensuring a comfortable living environment. In this paper, the authors report the experimental results of a study on the detailed characteristics of a laminated film-electrode and a laminated film-electrode packed-bed nonthermal plasma reactor, which are types of dielectric barrier discharge (DBD) reactor used for odor control. These plasma reactors can be potentially used for the decomposition of volatile organic compounds (VOCs) and reduction of NOx. The reactor is driven by a low-cost 60-Hz neon transformer. Removal efficiencies under various experimental conditions are studied. The complete decomposition of the main odor component, namely, NH3, is achieved in a dry environment. The retention times are investigated for the complete removal of NH3 in the case of the film-electrode plasma reactor and the film-electrode packed-bed plasma reactor. The removal efficiency of the former reactor is lower than that of the latter reactor. Mixing another odor component such as CH3CHO in the gas stream has no significant effect on NH3 removal efficiency

Hall effect of FeTe and Fe(Se_1-x_Te_x_) thin films

The Hall effect is investigated in thin-film samples of iron-chalcogenide superconductors in detail. The Hall coefficient (RH) of FeTe and Fe(Se1-xTex) exhibits a similar positive value around 300 K, indicating that the high-temperature normal state is dominated by hole-channel transport. FeTe exhibits a sign reversal from positive to negative across the transition to the low-temperature antiferromagnetic state, indicating the occurrence of drastic reconstruction in the band structure. The mobility analysis using the carrier density theoretically calculated reveals that the mobility of holes is strongly suppressed to zero, and hence the electric transport looks to be dominated by electrons. The Se substitution to Te suppresses the antiferromagnetic long-range order and induces superconductivity instead. The similar mobility analysis for Fe(Se0.4Te0.6) and Fe(Se0.5Te0.5) thin films shows that the mobility of electrons increases with decreasing temperature even in the paramagnetic state, and keeps sufficiently high values down to the superconducting transition temperature. From the comparison between FeTe and Fe(Se1-xTex), it is suggested that the coexistence of 'itinerant' carriers both in electron and hole channels is indispensable for the occurrence of superconductivity.Comment: 16 page, 6 figures, Proceedings of ISS-2010, to be published in Physica

Specific-heat study of superconducting and normal states in FeSe1-xTex (0.6<=x<=1) single crystals: Strong-coupling superconductivity, strong electron-correlation, and inhomogeneity

The electronic specific heat of as-grown and annealed single-crystals of FeSe1-xTex (0.6<=x<=1) has been investigated. It has been found that annealed single-crystals with x=0.6-0.9 exhibit bulk superconductivity with a clear specific-heat jump at the superconducting (SC) transition temperature, Tc. Both 2Delta_0/kBTc [Delta_0: the SC gap at 0 K estimated using the single-band BCS s-wave model] and Delta C/(gamma_n-gamma_0)Tc [Delta C$: the specific-heat jump at Tc, gamma_n: the electronic specific-heat coefficient in the normal state, gamma_0: the residual electronic specific-heat coefficient at 0 K in the SC state] are largest in the well-annealed single-crystal with x=0.7, i.e., 4.29 and 2.76, respectively, indicating that the superconductivity is of the strong coupling. The thermodynamic critical field has also been estimated. gamma_n has been found to be one order of magnitude larger than those estimated from the band calculations and increases with increasing x at x=0.6-0.9, which is surmised to be due to the increase in the electronic effective mass, namely, the enhancement of the electron correlation. It has been found that there remains a finite value of gamma_0 in the SC state even in the well-annealed single-crystals with x=0.8-0.9, suggesting an inhomogeneous electronic state in real space and/or momentum space.Comment: 22 pages, 1 table, 6 figures, Version 2 has been accepted for publication in J. Phys. Soc. Jp

Local antiferromagnetic exchange and collaborative Fermi surface as key ingredients of high temperature superconductors

Cuprates, ferropnictides and ferrochalcogenides are three classes of unconventional high-temperature superconductors, who share similar phase diagrams in which superconductivity develops after a magnetic order is suppressed, suggesting a strong interplay between superconductivity and magnetism, although the exact picture of this interplay remains elusive. Here we show that there is a direct bridge connecting antiferromagnetic exchange interactions determined in the parent compounds of these materials to the superconducting gap functions observed in the corresponding superconducting materials. High superconducting transition temperature is achieved when the Fermi surface topology matches the form factor of the pairing symmetry favored by local magnetic exchange interactions. Our result offers a principle guide to search for new high temperature superconductors.Comment: 12 pages, 5 figures, 1 table, 1 supplementary materia

Electronic Structure of Fe-Based Superconductors

The electronic structure of the Fe-based superconductors is discussed, mainly from the point of view of first principles calculations in relation to experimental data. Comparisons and contrasts with cuprates are made. The problem of reconciling experiments indicating an $s$ symmetry gap with experiments indicating line nodes is discussed and a possible resolution is given.Comment: Updated references. Additional discussio