209 research outputs found
Charge-stripe order in the electronic ferroelectric LuFe2O4
The structural features of the charge ordering states in LuFe2O4 are
characterized by in-situ cooling TEM observations from 300K down to 20K. Two
distinctive structural modulations, a major q1= (1/3, 1/3, 2) and a weak
q2=q1/10 + (0, 0, 3/2), have been well determined at the temperature of 20K.
Systematic analysis demonstrates that the charges at low temperatures are well
crystallized in a charge stripe phase, in which the charge density wave
behaviors in a non-sinusoidal fashion resulting in elemental electric dipoles
for ferroelectricity. It is also noted that the charge ordering and
ferroelectric domains often change markedly with lowering temperatures and
yields a rich variety of structural phenomena.Comment: 15 pages, 4 figure
Superconductivity Induced by Bond Breaking in the Triangular Lattice of IrTe2
IrTe2, a layered compound with a triangular iridium lattice, exhibits a
structural phase transition at approximately 250 K. This transition is
characterized by the formation of Ir-Ir bonds along the b-axis. We found that
the breaking of Ir-Ir bonds that occurs in Ir1-xPtxTe2 results in the
appearance of a structural critical point in the T = 0 limit at xc = 0.035.
Although both IrTe2 and PtTe2 are paramagnetic metals, superconductivity at Tc
= 3.1 K is induced by the bond breaking in a narrow range of x > xc in
Ir1-xPtxTe2. This result indicates that structural fluctuations can be involved
in the emergence of superconductivity.Comment: 10 pages, 4 figure
Delicate balance between ferroelectricity and antiferroelectricity in hexagonal InMnO3
The presence of ferroelectricity in hexagonal InMnO3 has been highly under debate. The results of our comprehensive experiments of low-temperature (T) polarization, transmission electron microscopy, and high-angle annular dark-field scanning TEM on well-controlled InMnO3 reveal that the ground state is ferroelectric with P63cm symmetry, but a nonferroelectric P3̄c1 state exists at high T and can be quenched to room temperature. We found that the competing ferroelectric and antiferroelectric phases coexist in mesoscopic scales and can be deliberately controlled by varying thermal treatments. © 2013 American Physical Society.open5
Trimer Formation and Metal-Insulator Transition in Orbital Degenerate Systems on a Triangular Lattice
As a prototypical self-organization in the system with orbital degeneracy, we
theoretically investigate trimer formation on a triangular lattice, as observed
in LiVO2. From the analysis of an effective spin-orbital coupled model in the
strong correlation limit, we show that the previously-proposed orbital-ordered
trimer state is not the lowest-energy state for a finite Hund's-rule coupling.
Instead, exploring the ground state in a wide range of parameters for a
multiorbital Hubbard model, we find an instability toward a different
orbital-ordered trimer state in the intermediately correlated regime in the
presence of trigonal crystal field. The trimer phase appears in the competing
region among a paramagnetic metal, band insulator, and Mott insulator. The
underlying mechanism is nesting instability of the Fermi surface by a
synergetic effect of Coulomb interactions and trigonal-field splitting. The
results are compared with experiments in triangularlattice compounds, LiVX2
(X=O, S, Se) and NaVO2.Comment: 4 pages, 4 figures, accepted for publication in J. Phys. Soc. Jp
Neurology
Contains research objectives and reports on six research projects.National Science Foundation (Grant G-16526)National Institutes of Health (Grant MH-04737-03)U.S. Public Health Service (B-3055-3)U.S. Public Health Service (B-3090-3)U.S. Public Health Service (MH-06175-01A1)Office of Naval Research (Nonr-1841(70))Air Force (AFOSR 155-63)Army Chemical Corps (DA- 18-108-405-CML-942
Neurology
Contains reports on six research projects.U. S. Public Health Service (B-3055-4, B-3090-4, MH-06175-02)U. S. Air Force (AF49(638)-1313)U.S. Navy. Office of Naval Research (Nonr-1841(70)
Universality in one dimensional orbital wave ordering in spinel and related compounds: an experimental perspective
Recent state-of-the-art crystallographic investigations of transition metal
spinel compounds have revealed that the d- orbital charge carriers undergo
ordering transitions with the formation of local "molecular bonding" units such
as dimers in MgTi2O4, octomers in CuIr2S4, and heptamers in AlV2O4. Herein, we
provide a unifying scheme involving one- dimensional orbital wave ordering
applicable to all of these spinels. The relative phase of the orbitals in the
chains is shown to be crucial to the formation of different local units, and
thus both the amplitude and phase of the orbital wave play important roles.
Examination of Horibe et al.'s [1] structure for AlV2O4 serves as the vehicle
for developing the general behavior for such orbital wave ordering. Ordered
AlV2O4 will be seen to organize into three equivalent chains in 2D Kagome
planes coupled so as to form units of three dimer bonds. Three additional
equivalent chains manifest a more complex tetramerization with three different
charge states and two different bonding schemes. The orbital wave ordering
scheme developed is extended to other spinel and related compounds with local
triangular transition metal coordination and partial filling of the t2g-d
orbitals
Synergistic Formation of Radicals by Irradiation with Both Vacuum Ultraviolet and Atomic Hydrogen: A Real-Time In Situ Electron Spin Resonance Study
We report on the surface modification of polytetrafluoroethylene (PTFE) as an
example of soft- and bio-materials that occur under plasma discharge by
kinetics analysis of radical formation using in situ real-time electron spin
resonance (ESR) measurements. During irradiation with hydrogen plasma,
simultaneous measurements of the gas-phase ESR signals of atomic hydrogen and
the carbon dangling bond (C-DB) on PTFE were performed. Dynamic changes of the
C-DB density were observed in real time, where the rate of density change was
accelerated during initial irradiation and then became constant over time. It
is noteworthy that C-DBs were formed synergistically by irradiation with both
vacuum ultraviolet (VUV) and atomic hydrogen. The in situ real-time ESR
technique is useful to elucidate synergistic roles during plasma surface
modification.Comment: 14 pages, 4 figure
Genotype of FLOWERING LOCUS T homologue contributes to flowering time differences in wild and cultivated roses
Rose flowers have long delighted humans as ornamental plants. To improve the ornamental value of roses it is necessary to understand the regulatory mechanisms of flowering. We previously found that flowering time is controlled by three minor quantitative trait loci (QTLs) and a major QTL co-localised with RoFT. In this study, we isolated three RoFT alleles encoding completely identical amino acid sequences from the parents of a mapping population. Correlation analysis of the RoFT genotypes and flowering time phenotypes in the mapping population showed that the RoFT_f and RoFT_g alleles contribute to the early-flowering phenotype, while the RoFT_e allele contributes to the late-flowering phenotype. We developed two novel cleaved amplified polymorphic sequence (CAPS) markers based on the genomic sequences of the RoFT alleles and clearly showed that the relationship between RoFT genotype and flowering time was applicable to 12 of 13 cultivated roses grown at the Higashiyama Botanical Gardens, Japan. Allele-specific expression analysis using a reverse transcription CAPS assay suggested that these RoFT alleles are regulated differentially at the transcription level. Furthermore, transgenic Arabidopsis thaliana plants ectopically expressing the RoFT gene showed an early-flowering phenotype. Conversely, in roses, RoFT was continuously expressed after floral bud formation, and RoFT transcript accumulation reached its peak after that of the floral meristem identity gene RoAP1b. These data suggest that RoFT may be essential not only for floral transition but also for normal floral development and flowering in roses
Pinning of stripes by local structural distortions in cuprate high-Tc superconductors
We study the spin-density wave (stripe) instability in lattices with mixed
low-temperature orthorhombic (LTO) and low-temperature tetragonal (LTT) crystal
symmetry. Within an explicit mean-field model it is shown how local LTT regions
act as pinning centers for static stripe formation. We calculate the
modulations in the local density of states near these local stripe regions and
find that mainly the coherence peaks and the van Hove singularity (VHS) are
spatially modulated. Lastly, we use the real-space approach to simulate recent
tunneling data in the overdoped regime where the VHS has been detected by
utilizing local normal state regions.Comment: Conference proceedings for Stripes1
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