391 research outputs found
Observation of Macroscopic Structural Fluctuations in bcc Solid 4He
We report neutron diffraction studies of low density bcc and hcp solid 4He.
In the bcc phase, we observed a continuous dynamical behaviour involving
macroscopic structural changes of the solid. The dynamical behaviour takes
place in a cell full of solid, and therefore represents a solidsolid
transformation. The structural changes are consistent with a gradual rotation
of macroscopic grains separated by low angle grain boundaries. We suggest that
these changes are triggered by random momentary vibrations of the experimental
system. An analysis of Laue diffraction patterns indicates that in some cases
these structural changes, once initiated by a momentary impulse, seem to
proceed at a constant rate over times approaching an hour. The energy
associated with these macroscopic changes appears to be on the order of kT.
Under similar conditions (temperature and pressure), these effects were absent
in the hcp phase.Comment: 14 pages, 6 figure, accepted for PR
Epitaxial checkerboard arrangement of nanorods in ZnMnGaO4 films studied by x-ray diffraction
The intriguing nano-structural properties of a ZnMnGaO4 film epitaxially
grown on MgO (001) substrate have been investigated using synchrotron
radiation-based x-ray diffraction. The ZnMnGaO4 film consisted of a
self-assembled checkerboard (CB) structure with perfectly aligned and regularly
spaced vertical nanorods. The lattice parameters of the orthorhombic and
rotated tetragonal phases of the CB structure were analyzed using H-K, H-L, and
K-L cross sections of the reciprocal space maps measured around various
symmetric and asymmetric reflections of the spinel structure. We demonstrate
that the symmetry of atomic displacements at the phases boundaries provides the
means for coherent coexistence of two domains types within the volume of the
film
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
Amorphization under fracture surface in hydrogen-charged and low- temperature tensile-tested austenitic stainless steel
The microstructure just below the fracture surface in hydrogen-charged stable austenitic SUS 316L stainless steel, which was subjected to a low strain rate tensile test at −70°C, was studied by a combination of the focused-ion-beam method and transmission electron microscopy. An amorphous region with a chemical composition almost identical to that of the polycrystalline region was found under the lath-like structure on the fracture surface, although no deterioration of tensile properties by hydrogen appeared. In the amorphous region, band-like regions with wavy contrasts were observed, which were often accompanied by cracks at the boundaries. The presence of the amorphous region with band-like regions implies that amorphization occurred due to high-density vacancies accompanied by agglomerations of excess vacancies in the hydrogen-charged SUS 316L stainless steel that was tensile-tested at low temperatures
Structural Transition of Li2RuO3 Induced by Molecular-Orbit Formation
A pseudo honeycomb system Li2RuO3 exhibits a second-order-like transition at
temperature T=Tc=540 K to a low-T nonmagnetic phase with a significant lattice
distortion forming Ru-Ru pairs. For this system, we have calculated the band
structure, using the generalized gradient approximation (GGA) in both the high-
and low- T phases, and found that the results of the calculation can naturally
explain the insulating behavior observed in the low-T phase. The detailed
characters of the Ru 4d t2g bands obtained by the tight-binding fit to the
calculated dispersion curves show clear evidence that the structural transition
is driven by the formation of the Ru-Ru molecular-orbits, as proposed in our
previous experimental studies.Comment: 5 pages, 5 figures, 4 tables, submitted to J. Phys. Soc. Jp
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
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
Wigner Functions on a Lattice
The Wigner functions on the one dimensional lattice are studied. Contrary to
the previous claim in literature, Wigner functions exist on the lattice with
any number of sites, whether it is even or odd. There are infinitely many
solutions satisfying the conditions which reasonable Wigner functions should
respect. After presenting a heuristic method to obtain Wigner functions, we
give the general form of the solutions. Quantum mechanical expectation values
in terms of Wigner functions are also discussed.Comment: 11 pages, no figures, REVTE
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
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