Soft x-ray absorption spectroscopy study of the electronic structures of the MnFe Prussian blue analogs (RbxBay)Mn[3-(x+2y)]/2[Fe(CN)6]H2O

The electronic structures of Prussian blue analog (RbxBay) Mn[3-(x+2y)]/2[Fe(CN)(6)] cyanides have been investigated by employing soft x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD) at the Fe and Mn L (2p) edges. The measured XAS spectra have been analyzed with the configuration-interaction (CI) cluster model calculations. The valence states of the Fe and Mn ions are found to be Fe2+-Fe3+ mixed valent, with an average valency of v(Fe) similar to 2.8 and nearly divalent (Mn2+), respectively. Our Mn/Fe 2p XMCD study supports that Mn2+ ions are in the high-spin states while Fe2+-Fe3+ ions are in the low-spin states. The Fe and Mn 2p XAS spectra are found to be essentially the same for 80 <= T <= 300 K, suggesting that a simple charge transfer upon cooling from Fe3+- CN-Mn2+ to Fe (2+)-CN-Mn3+ does not occur in (RbxBay) Mn[3-(x+2y)]/2[Fe(CN)(6)]. According to the CI cluster model analysis, it is necessary to take into account both the ligand-to-metal charge transfer and the metal-to-ligand charge transfer in describing Fe 2p XAS, while the effect of charge transfer is negligible in describing Mn 2p XAS. The CI cluster model analysis also shows that the trivalent Fe3+ ions have a strong covalent bonding with the C equivalent to N ligands and are under a large crystal-field energy of 10Dq similar to 3 eV, in contrast to the weak covalency effect and a small 10Dq similar to 0.6 eV for the divalent Mn2+ ions.1

Correlated Electronic Structures and the Phase Diagram of Hydrocarbon-based Superconductors

We have investigated correlated electronic structures and the phase diagram of electron-doped hydrocarbon molecular solids, based on the dynamical mean-field theory. We have found that the ground state of hydrocarbon-based superconductors such as electron-doped picene and coronene is a multi-band Fermi liquid, while that of non-superconducting electron-doped pentacene is a single-band Fermi liquid in the proximity of the metal-insulator transition. The size of the molecular orbital energy level splitting plays a key role in producing the superconductivity of electron-doped hydrocarbon solids. The multi-band nature of hydrocarbon solids would boost the superconductivity through the enhanced density of states at the Fermi level.X11910sciescopu

Observation of a kink during the formation of the Kondo resonance band in a heavy-fermion system

We have shown that the kink behavior in the spectral function of a heavy fermion can appear during the formation of the Kondo resonance (KR) band and the hybridization gap. We have investigated the heavy fermion compound CeCoGe2, using a combined approach of the density functional theory and the dynamical mean field theory. Low temperature T spectral functions show dispersive KR states, similarly to the recent experimental observation. During the evolution from the non-f conduction band state at high T to the dispersive KR band state at low T, which have topologically different band shapes, we have found the existence of kinks in the non-f spectral function near the Fermi level E-F. The observation of kink is clearly in correspondence with the multiple temperature scales of the formation of the KR band.X1186sciescopu

Numerical analysis for 137CS on seabed sediment including atmospheric deposition near the Fukushima coastal area

Radionuclides were released into the atmosphere and ocean from the accident at the Fukushima Daiichi Nuclear Power Plant (NPP) in March 2011. Numerical simulations were performed to evaluate the distribution of 137Cs in the ocean with considering directly release and deposition from the atmosphere. Calculated concentrations of 137Cs in the sea water and seabed are compared with the measured data, and atmospheric transport model has been also used to calculate the rates of atmospheric deposition on the sea surface. Lots of atmospheric deposition was occurred on sea surface in northeast direction from Fukushima NPP due to westerly wind and precipitation on March 15-31, 2011. Most modelling for the marine dispersion of 137Cs after Fukushima accident was considered as a perfectly conservative radionuclide, thus scavenging processes and adsorption on seabed sediments are neglected. The processes of the non-conservative from the numerical simulations have been well described and the calculated results are also in agreement with the measured data. The concentrations of 137Cs in seabed sediments were mainly contributed by the atmospheric deposition and long residence time showed in northeast coastal area off Fukushima NPP

Should we measure plutonium concentrations in marine sediments near Fukushima?

Pu contamination originating from Fukushima accident has not been detected in marine sediment samples collected outside a 30 km circle around the plant. It is shown, by means of numerical modelling, that if any impact from the accident has occurred, this would remain in a very close area to Fukushima because of the low Pu mobility in the marine environment. Since the situation inside the 30 km zone remains unknown, further studies on the determination of Pu isotopes in sediments within this area are required

Local scale marine modelling of Fukushima releases. Assessment of water and sediment contamination and sensitivity to water circulation description

The dispersion of 137Cs released from Fukushima nuclear power plant to the sea after the March 11th 2011 tsunami has been studied using numerical models. The 3D dispersion model consists of an advec tion/diffusion equation with terms describing uptake/release reactions between water and seabed sedi ments. The dispersion model has been fed with daily currents provided by HYCOM and JCOPE2 ocean models. Seabed sediment 137Cs patterns obtained using both current data set have been compared. The impact of tides and of atmospheric deposition has been evaluated as well. It has been also found that a 2-step kinetic model (two consecutive reversible reactions) for describing water/sediment interactions produces better results than a 1-step model (one single reversible reactio

Topological Structure of Dense Hadronic Matter

We present a summary of work done on dense hadronic matter, based on the Skyrme model, which provides a unified approach to high density, valid in the large $N_c$ limit. In our picture, dense hadronic matter is described by the {\em classical} soliton configuration with minimum energy for the given baryon number density. By incorporating the meson fluctuations on such ground state we obtain an effective Lagrangian for meson dynamics in a dense medium. Our starting point has been the Skyrme model defined in terms of pions, thereafter we have extended and improved the model by incorporating other degrees of freedom such as dilaton, kaons and vector mesons.Comment: 13 pages, 8 figures, Talk given at the KIAS-APCTP Symposium in Astro-Hadron Physics "Compact Stars: Quest for New States of Dense Matter", November 10-14, 2003, Seoul, Korea, published by World Scientific. Based on talk by B.-Y. Par

Temperature-dependent evolutions of excitonic superfluid plasma frequency in a srong excitonic insulator candidate, Ta2_2NiSe5_5

We investigate an interesting anisotropic van der Waals material, Ta$_{2}$NiSe$_{5}$, using optical spectroscopy. Ta$_{2}$NiSe$_{5}$ has been known as one of the few excitonic insulators proposed over 50 years ago. Ta$_{2}$NiSe$_{5}$ has quasi-one dimensional chains along the $a$-axis. We have obtained anisotropic optical properties of a single crystal Ta$_{2}$NiSe$_{5}$ along the $a$- and $c$-axes. The measured $a$- and $c$-axis optical conductivities exhibit large anisotropic electronic and phononic properties. With regard to the $a$-axis optical conductivity, a sharp peak near 3050 cm$^{-1}$ at 9 K, with a well-defined optical gap ($\Delta^{EI} \simeq$ 1800 cm$^{-1}$) and a strong temperature-dependence, is observed. With an increase in temperature, this peak broadens and the optical energy gap closes around $\sim$325 K($T_c^{EI}$). The spectral weight redistribution with respect to the frequency and temperature indicates that the normalized optical energy gap ($\Delta^{EI}(T)/\Delta^{EI}(0)$) is $1-(T/T_c^{EI})^2$. The temperature-dependent superfluid plasma frequency of the excitonic condensation in Ta$_{2}$NiSe$_{5}$ has been determined from measured optical data. Our findings may be useful for future research on excitonic insulators.Comment: 17 pages, 5 figure