77 research outputs found
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
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
Effect of sustained postnatal systemic inflammation on hippocampal volume and function in mice.
BACKGROUND: Premature infants are at risk for persistent neurodevelopmental impairment. Children born preterm often exhibit reduced hippocampal volumes that correlate with deficits in working memory. Perinatal inflammation is associated with preterm birth and brain abnormalities. Here we examine the effects of postnatal systemic inflammation on the developing hippocampus in mice.
METHODS: Pups received daily intraperitoneal injections of lipopolysaccharide (LPS) or saline between days 3 and 13. Ex vivo magnetic resonance imaging (MRI) and microscopic analysis of brain tissue was performed on day 14. Behavioral testing was conducted at 8-9 wk of age.
RESULTS: MR and microscopic analysis revealed a 15-20% reduction in hippocampal volume in LPS-treated mice compared with controls. Behavioral testing revealed deficits in hippocampal-related tasks in LPS-treated animals. Adult mice exposed to LPS during the postnatal period were unable to select a novel environment when re-placed within a 1-min delay, were less able to remember a familiar object after a 1-h delay, and had impaired retention of associative fear learning after 24 h.
CONCLUSION: Systemic inflammation sustained during the postnatal period contributes to reduced hippocampal volume and deficits in hippocampus-dependent working memory. These findings support the novel and emerging concept that sustained systemic inflammation contributes to neurodevelopmental impairment among preterm infants
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