Slater to Mott crossover in the metal to insulator transition of Nd2Ir2O7

We present an angle-resolved photoemission study of the electronic structure of the three-dimensional pyrochlore iridate Nd2Ir2O7 through its magnetic metal-insulator transition. Our data reveal that metallic Nd2Ir2O7 has a quadratic band, touching the Fermi level at the Gamma point, similarly to that of Pr2Ir2O7. The Fermi node state is, therefore, a common feature of the metallic phase of the pyrochlore iridates. Upon cooling below the transition temperature, this compound exhibits a gap opening with an energy shift of quasiparticle peaks like a band gap insulator. The quasiparticle peaks are strongly suppressed, however, with further decrease of temperature, and eventually vanish at the lowest temperature, leaving a non-dispersive flat band lacking long-lived electrons. We thereby identify a remarkable crossover from Slater to Mott insulators with decreasing temperature. These observations explain the puzzling absence of Weyl points in this material, despite its proximity to the zero temperature metal-insulator transition

Doping-Dependent and Orbital-Dependent Band Renormalization in Ba(Fe_1-xCo_x)_2As_2 Superconductors

Angle resolved photoemission spectroscopy of Ba(Fe1-xCox)2As2 (x = 0.06, 0.14, and 0.24) shows that the width of the Fe 3d yz/zx hole band depends on the doping level. In contrast, the Fe 3d x^2-y^2 and 3z^2-r^2 bands are rigid and shifted by the Co doping. The Fe 3d yz/zx hole band is flattened at the optimal doping level x = 0.06, indicating that the band renormalization of the Fe 3d yz/zx band correlates with the enhancement of the superconducting transition temperature. The orbital-dependent and doping-dependent band renormalization indicates that the fluctuations responsible for the superconductivity is deeply related to the Fe 3d orbital degeneracy.Comment: 5 pages, 4 figure

Electronic Structure Calculation by First Principles for Strongly Correlated Electron Systems

Recent trends of ab initio studies and progress in methodologies for electronic structure calculations of strongly correlated electron systems are discussed. The interest for developing efficient methods is motivated by recent discoveries and characterizations of strongly correlated electron materials and by requirements for understanding mechanisms of intriguing phenomena beyond a single-particle picture. A three-stage scheme is developed as renormalized multi-scale solvers (RMS) utilizing the hierarchical electronic structure in the energy space. It provides us with an ab initio downfolding of the global band structure into low-energy effective models followed by low-energy solvers for the models. The RMS method is illustrated with examples of several materials. In particular, we overview cases such as dynamics of semiconductors, transition metals and its compounds including iron-based superconductors and perovskite oxides, as well as organic conductors of kappa-ET type.Comment: 44 pages including 38 figures, to appear in J. Phys. Soc. Jpn. as an invited review pape

d- and f-orbital correlations in the REFeAsO compounds

We estimate theoretically the strength of the local Coulomb interaction for the Fe 3d and Ce 4f shells in the REFeAsO compunds. In LaFeAsO and CeFeAsO we obtain values of the local Coulomb interaction parameter U for both Fe and Ce which are larger than those of elemental Fe and Ce metals. The Fe 3d bandwidth of REFeAsO is found to increase slightly as one moves along the RE-series. Using a combined local density approximation and dynamical mean-field theory (LDA+DMFT) approach, we study the behaviour of the localized 4f states along the rare-earth oxyarsenides REFeAsO series (RE=Ce,Pr,Nd). In CeFeAsO the occupied Ce 4f band is located just below the Fe 3d band leading possibly to a Kondo screening of the 4f local moment under applied pressure, while the unscreened local moment behaviour is expected for the Pr and Nd compounds.Comment: 7 pages, 2 figures, 1 tabl

Immune stress in late pregnant rats decreases length of gestation and fecundity, and alters later cognitive and affective behaviour of surviving pre-adolescent offspring

Immune challenge during pregnancy is associated with preterm birth and poor perinatal development. The mechanisms of these effects are not known. 5α-Pregnan-3α-ol-20-one (3α,5α-THP), the neuroactive metabolite of progesterone, is critical for neurodevelopment and stress responses, and can influence cognition and affective behaviours. To develop an immune challenge model of preterm birth, pregnant Long–Evans rat dams were administered lipopolysaccharide [LPS; 30 μg/kg/ml, intraperitoneal (IP)], interleukin-1β (IL-1β; 1 μg/rat, IP) or vehicle (0.9% saline, IP) daily on gestational days 17–21. Compared to control treatment, prenatal LPS or IL-1β reduced gestational length and the number of viable pups born. At 28–30 days of age, male and female offspring of mothers exposed to prenatal IL-1β had reduced cognitive performance in the object recognition task compared to controls. In females, but not males, prenatal IL-1β reduced anxiety-like behaviour, indicated by entries to the centre of an open field. In the hippocampus, progesterone turnover to its 5α-reduced metabolites was lower in prenatally exposed IL-1β female, but not in male offspring. IL-1β-exposed males and females had reduced oestradiol content in hippocampus, medial prefrontal cortex and diencephalon compared to controls. Thus, immune stress during late pregnancy reduced gestational length and negatively impacted birth outcomes, hippocampal function and central neurosteroid formation in the offspring

Impact of intermittent water supply on water quality in Lebanon

Lebanon in general and its capital, Beirut, suffer from water shortage due to the increasing water demand and the lack of proper management despite its abundant water resources. An intermittent water supply strategy was implemented in order to minimise deficiency problems. This, however, can seriously affect water quality due to the potential suction of non-potable water by negative pressures, biofilm detachment, and microbial re-growth especially when static conditions occur. Intermittent supplies also entail storing water in household tanks to satisfy demand during no-flow periods, and these tanks often encourage bacterial re-growth. Dumping of disinfectants in order to circumvent bacterial presence and the subsequent formation of undesirable byproducts is another concern. A study was conducted in Beirut over an eight-month period, during which samples were collected from household tanks and drinking water taps of Beirut's network. This paper presents the findings of the study and highlights key aspects in intermittent water supply systems. Copyright © 2006 Inderscience Enterprises Ltd.*AGFUND WHO CEHA, 2003, NAT SEM STRAT PROT Q; AYOUB G, 2003, NAT SEM STRAT PROT Q; Boe-Hansen R, 2002, WATER RES, V36, P4477, DOI 10.1016-S0043-1354(02)00191-4; CLARK RM, 1995, J WATER RES PL-ASCE, V121, P423, DOI 10.1061-(ASCE)0733-9496(1995)121:6(423); Clark RM, 1998, J ENVIRON ENG-ASCE, V124, P1203, DOI 10.1061-(ASCE)0733-9372(1998)124:12(1203); Coelho ST, 2003, WA SCI TECHNOL, V3, P119; Delahaye E, 2003, WATER RES, V37, P3689, DOI 10.1016-S0043-1354(03)00288-4; Fass S, 2003, WATER RES, V37, P493, DOI 10.1016-S0043-1354(02)00362-7; Geldreich EE, 1996, MICROBIAL QUALITY WA; LECHEVALLIER MW, 2003, J WATER HEALTH, V1, P1; Lu W, 1999, WATER RES, V33, P827, DOI 10.1016-S0043-1354(98)00229-2; Menaia J, 2003, WA SCI TECHNOL, V3, P209; METNI M, 2002, THESIS AM U BEIRUT; *MOE, 2001, LEB MIN ENV STAT ENV; Momba MNB, 1998, WATER SCI TECHNOL, V38, P283, DOI 10.1016-S0273-1223(98)00703-3; Ollos PJ, 1998, WATER SCI TECHNOL, V38, P275, DOI 10.1016-S0273-1223(98)00702-1; Percival SL, 1998, WATER RES, V32, P243, DOI 10.1016-S0043-1354(97)00132-2; Powell JC, 2000, WATER RES, V34, P117, DOI 10.1016-S0043-1354(99)00097-4; Rompre A, 2000, WATER SCI TECHNOL, V41, P287; Sarin P, 2004, WATER RES, V38, P1259, DOI 10.1016-j.watres.2003.11.022; Tokajian S, 2003, WATER SCI TECHNOL, V47, P229; VIEIRA P, 2003, ACCOUNTING INFLUENCE; WHO, 1995, GUID DRINK WAT QUAL, V154