778 research outputs found
First evidence for charge ordering in NaVO from Raman spectroscopy
We argue on the basis of symmetry selection rules and Raman scattering
spectra that NaVO undergoes a charge ordering phase transition at
T=34 K. Such a transition is characterized by the redistribution of the
charges at the phase transition and corresponds to the change of the vanadium
ions, from uniform V to two different V and V states. In
the low temperature phase the V ions are forming a "zig-zag" ladder
structure along the {\bf b}-axis, consistent with the symmetry of the P2/b
space group.Comment: to be published in solid state communication
Room temperature midinfrared electroluminescence from GaInAsSbP light emitting diodes. .
Room temperature electroluminescence in the midinfrared near 4 µm is reported from GaInAsSbP light emitting diodes grown on GaSb by liquid phase epitaxy. Comparison of the electro- and photoluminescence revealed that light is generated on the p side of the diode. The energy shift (24 meV) is consistent with band gap narrowing and recombination via band tail states due to the Zn doping (1×1018 cm−3) in the p layer of the structure. The temperature dependent behavior of the luminescence and the improved emission intensity was attributed to recombination from localized states arising from electrostatic potential fluctuations due to compositional inhomogeneities in these alloys
Tangled nonlinear driven chain reactions of all optical singularities
Dynamics of polarization optical singularities chain reactions in generic
elliptically polarized speckle fields created in photorefractive crystal LiNbO3
was investigated in details Induced speckle field develops in the tens of
minutes scale due to photorefractive 'optical damage effect' induced by
incident beam of He-Ne laser. It was shown that polarization singularities
develop through topological chain reactions of developing speckle fields driven
by photorefractive nonlinearities induced by incident laser beam. All optical
singularities (C points, optical vortices, optical diabolos,) are defined by
instantaneous topological structure of the output wavefront and are tangled by
singular optics lows. Therefore, they have develop in tangled way by six
topological chain reactions driven by nonlinear processes in used nonlinear
medium (photorefractive LiNbO3:Fe in our case): C-points and optical diabolos
for right (left) polarized components domains with orthogonally left (right)
polarized optical vortices underlying them. All elements of chain reactions
consist from loop and chain links when nucleated singularities annihilated
directly or with alien singularities in 1:9 ratio. The topological reason of
statistics was established by low probability of far enough separation of born
singularities pair from existing neighbor singularities during loop
trajectories. Topology of developing speckle field was measured and analyzed by
dynamic stokes polarimetry with few seconds' resolution. The hierarchy of
singularities govern scenario of tangled chain reactions was defined. The
useful space-time data about peculiarities of optical damage evolution were
obtained from existence and parameters of 'islands of stability' in developing
speckle fields.Comment: 11 pages, 12 figure
Premartensitic Transition in Ni2+xMn1-xGa Heusler Alloys
The temperature dependencies of the resistivity and magnetization of a series
of Ni2+XMn1-XGa (X = 0 - 0.09) alloys were investigated. Along with the
anomalies associated with ferromagnetic and martensitic transitions,
well-defined anomalies were observed at the temperature of premartensitic
transformation. The premartensitic phase existing in a temperature range 200 -
260 K in the stoichiometric Ni2MnGa is suppressed by the martensitic phase with
increasing Ni content and vanishes in Ni2.09Mn0.91Ga composition
Renormalization-group approach to the stochastic Navier--Stokes equation: Two-loop approximation
The field theoretic renormalization group is applied to the stochastic
Navier--Stokes equation that describes fully developed fluid turbulence. The
complete two-loop calculation of the renormalization constant, the
function, the fixed point and the ultraviolet correction exponent is performed.
The Kolmogorov constant and the inertial-range skewness factor, derived to
second order of the \eps expansion, are in a good agreement with the
experiment. The possibility of the extrapolation of the \eps expansion beyond
the threshold where the sweeping effects become important is demonstrated on
the example of a Galilean-invariant quantity, the equal-time pair correlation
function of the velocity field. The extension to the -dimensional case is
briefly discussed.Comment: 20 pages, 3 figure
- …