437 research outputs found
Peierls Mechanism of the Metal-Insulator Transition in Ferromagnetic Hollandite K2Cr8O16
Synchrotron X-ray diffraction experiment shows that the metal-insulator
transition occurring in a ferromagnetic state of a hollandite
KCrO is accompanied by a structural distortion from the
tetragonal to monoclinic phase with a
supercell. Detailed electronic structure
calculations demonstrate that the metal-insulator transition is caused by a
Peierls instability in the quasi-one-dimensional column structure made of four
coupled Cr-O chains running in the -direction, leading to the formation of
tetramers of Cr ions below the transition temperature. This furnishes a rare
example of the Peierls transition of fully spin-polarized electron systems.Comment: Phys. Rev. Lett., in press, 5 pages, 3 figure
Important Roles of Te 5p and Ir 5d Spin-orbit Interactions on the Multi-band Electronic Structure of Triangular Lattice Superconductor Ir1-xPtxTe2
We report an angle-resolved photoemission spectroscopy (ARPES) study on a
triangular lattice superconductor IrPtTe in which the Ir-Ir
or Te-Te bond formation, the band Jahn-Teller effect, and the spin-orbit
interaction are cooperating and competing with one another. The Fermi surfaces
of the substituted system are qualitatively similar to the band structure
calculations for the undistorted IrTe with an upward chemical potential
shift due to electron doping. A combination of the ARPES and the band structure
calculations indicates that the Te spin-orbit interaction removes the
orbital degeneracy and induces type spin-orbit
coupling near the A point. The inner and outer Fermi surfaces are entangled by
the Te and Ir spin-orbit interactions which may provide exotic
superconductivity with singlet-triplet mixing.Comment: 10 pages, 4 figure
Te 5p orbitals bring three-dimensional electronic structure to two-dimensional Ir0.95Pt0.05Te2
We have studied the nature of the three-dimensional multi-band electronic
structure in the twodimensional triangular lattice Ir1-xPtxTe2 (x=0.05)
superconductor using angle-resolved photoemission spectroscopy (ARPES), x-ray
photoemission spectroscopy (XPS) and band structure calculation. ARPES results
clearly show a cylindrical (almost two-dimensional) Fermi surface around the
zone center. Near the zone boundary, the cylindrical Fermi surface is truncated
into several pieces in a complicated manner with strong three-dimensionality.
The XPS result and the band structure calculation indicate that the strong Te
5p-Te 5p hybridization between the IrTe2 triangular lattice layers is
responsible for the three-dimensionality of the Fermi surfaces and the
intervening of the Fermi surfaces observed by ARPES.Comment: 5 pages, 4 figure
Excitonic Bose-Einstein condensation in Ta2NiSe5 above room temperature
We show that finite temperature variational cluster approximation (VCA)
calculations on an extended Falicov-Kimball model can reproduce angle-resolved
photoemission spectroscopy (ARPES) results on Ta2NiSe5 across a
semiconductor-to-semiconductor structural phase transition at 325 K. We
demonstrate that the characteristic temperature dependence of the flat-top
valence band observed by ARPES is reproduced by the VCA calculation on the
realistic model for an excitonic insulator only when the strong excitonic
fluctuation is taken into account. The present calculations indicate that
Ta2NiSe5 falls in the Bose-Einstein condensation regime of the excitonic
insulator state.Comment: 21 pages(5 figures
Synchronous Symmetry Breaking in Neurons with Different Neurite Counts
As neurons develop, several immature processes (i.e., neurites) grow out of the cell body. Over time, each neuron breaks symmetry when only one of its neurites grows much longer than the rest, becoming an axon. This symmetry breaking is an important step in neurodevelopment, and aberrant symmetry breaking is associated with several neuropsychiatric diseases, including schizophrenia and autism. However, the effects of neurite count in neuronal symmetry breaking have never been studied. Existing models for neuronal polarization disagree: some predict that neurons with more neurites polarize up to several days later than neurons with fewer neurites, while others predict that neurons with different neurite counts polarize synchronously. We experimentally find that neurons with different neurite counts polarize synchronously. We also show that despite the significant differences among the previously proposed models, they all agree with our experimental findings when the expression levels of the proteins responsible for symmetry breaking increase with neurite count. Consistent with these results, we observe that the expression levels of two of these proteins, HRas and shootin1, significantly correlate with neurite count. This coordinated symmetry breaking we observed among neurons with different neurite counts may be important for synchronized polarization of neurons in developing organisms
Vascular Endothelial Adrenomedullin-RAMP2 System Is Essential for Vascular Integrity and Organ Homeostasis
信州大学博士(医学)・学位論文・平成25年3月31日授与(甲第935号)・小山 晃英Background-Revealing the mechanisms underlying the functional integrity of the vascular system could make available novel therapeutic approaches. We previously showed that knocking out the widely expressed peptide adrenomedullin (AM) or receptor activity-modifying protein 2 (RAMP2), an AM-receptor accessory protein, causes vascular abnormalities and is embryonically lethal. Our aim was to investigate the function of the vascular AM-RAMP2 system directly. Methods and Results-We generated endothelial cell-specific RAMP2 and AM knockout mice (E-RAMP2(-/-) and E-AM(-/-)). Most E-RAMP2(-/-) mice died perinatally. In surviving adults, vasculitis occurred spontaneously. With aging, E-RAMP2(-/-) mice showed severe organ fibrosis with marked oxidative stress and accelerated vascular senescence. Later, liver cirrhosis, cardiac fibrosis, and hydronephrosis developed. We next used a line of drug-inducible E-RAMP2(-/-) mice (DI-E-RAMP2(-/-)) to induce RAMP2 deletion in adults, which enabled us to analyze the initial causes of the aforementioned vascular and organ damage. Early after the induction, pronounced edema with enhanced vascular leakage occurred. In vitro analysis revealed the vascular leakage to be caused by actin disarrangement and detachment of endothelial cells. We found that the AM-RAMP2 system regulates the Rac1-GTP/RhoA-GTP ratio and cortical actin formation and that a defect in this system causes the disruption of actin formation, leading to vascular and organ damage at the chronic stage after the gene deletion. Conclusions-Our findings show that the AM-RAMP2 system is a key determinant of vascular integrity and homeostasis from prenatal stages through adulthood. Furthermore, our models demonstrate how endothelial cells regulate vascular integrity and how their dysregulation leads to organ damage. (Circulation. 2013;127:842-853.)ArticleCIRCULATION. 127(7):842-853 (2013)journal articl
Peierls Mechanism of the Metal-insulator Transition in Ferromagnetic Hollandite K 2Cr 8O 16
Synchrotron x-ray diffraction experiment shows that the metal-insulator transition occurring in a ferromagnetic state of a hollandite K 2Cr 8O 16 is accompanied by a structural distortion from the tetragonal I4/m to monoclinic P112 1/a phase with a √2×√2×1 supercell. Detailed electronic structure calculations demonstrate that the metal-insulator transition is caused by a Peierls instability in the quasi-one-dimensional column structure made of four coupled Cr-O chains running in the c direction, leading to the formation of tetramers of Cr ions below the transition temperature. This provides a rare example of the Peierls transition of fully spin-polarized electron systems. © 2011 American Physical Society.Japan Society for the Promotion of Science, JSPS: 19052004, 21224008, 22244041, 22540363
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