2,876 research outputs found
Dynamical Susceptibility in KDP-type Crysals above and below Tc II
The path probability method (PPM) in the tetrahedron-cactus approximation is
applied to the Slater-Takagi model with dipole-dipole interaction for
KH2PO4-type hydrogen-bonded ferroelectric crystals in order to derive a small
dip structure in the real part of dynamical susceptibility observed at the
transition temperature Tc. The dip structure can be ascribed to finite
relaxation times of electric dipole moments responsible for the first order
transition with contrast to the critical slowing down in the second order
transition. The light scattering intensity which is related to the imaginary
part of dynamical susceptibility is also calculated above and below the
transition temperature and the obtained central peak structure is consistent
with polarization fluctuation modes in Raman scattering experiments.Comment: 8 pages, 11 figure
Derivation of the particle dynamics from kinetic equations
We consider the microscopic solutions of the Boltzmann-Enskog equation
discovered by Bogolyubov. The fact that the time-irreversible kinetic equation
has time-reversible microscopic solutions is rather surprising. We analyze this
paradox and show that the reversibility or irreversibility property of the
Boltzmann-Enskog equation depends on the considered class of solutions. If the
considered solutions have the form of sums of delta-functions, then the
equation is reversible. If the considered solutions belong to the class of
continuously differentiable functions, then the equation is irreversible. Also,
we construct the so called approximate microscopic solutions. These solutions
are continuously differentiable and they are reversible on bounded time
intervals. This analysis suggests a way to reconcile the time-irreversible
kinetic equations with the time-reversible particle dynamics. Usually one tries
to derive the kinetic equations from the particle dynamics. On the contrary, we
postulate the Boltzmann-Enskog equation or another kinetic equation and treat
their microscopic solutions as the particle dynamics. So, instead of the
derivation of the kinetic equations from the microdynamics we suggest a kind of
derivation of the microdynamics from the kinetic equations.Comment: 18 pages; some misprints have been corrected, some references have
been adde
Magneto-infrared modes in InAs-AlSb-GaSb coupled quantum wells
We have studied a series of InAs/GaSb coupled quantum wells using
magneto-infrared spectroscopy for high magnetic fields up to 33T within
temperatures ranging from 4K to 45K in both Faraday and tilted field
geometries. This type of coupled quantum wells consists of an electron layer in
the InAs quantum well and a hole layer in the GaSb quantum well, forming the
so-called two dimensional electron-hole bilayer system. Unlike the samples
studied in the past, the hybridization of the electron and hole subbands in our
samples is largely reduced by having narrower wells and an AlSb barrier layer
interposed between the InAs and the GaSb quantum wells, rendering them weakly
hybridized. Previous studies have revealed multiple absorption modes near the
electron cyclotron resonance of the InAs layer in moderately and strongly
hybridized samples, while only a single absorption mode was observed in the
weakly hybridized samples. We have observed a pair of absorption modes
occurring only at magnetic fields higher than 14T, which exhibited several
interesting phenomena. Among which we found two unique types of behavior that
distinguishes this work from the ones reported in the literature. This pair of
modes is very robust against rising thermal excitations and increasing magnetic
fields alligned parallel to the heterostructures. While the previous results
were aptly explained by the antilevel crossing gap due to the hybridization of
the electron and hole wavefunctions, i.e. conduction-valence Landau level
mixing, the unique features reported in this paper cannot be explained within
the same concept. The unusual properties found in this study and their
connection to the known models for InAs/GaSb heterostructures will be
disccused; in addition, several alternative ideas will be proposed in this
paper and it appears that a spontaneous phase separation can account for most
of the observed features
Determining Neutrino Mass Hierarchy by Precision Measurements in Electron and Muon Neutrino Disappearance Experiments
Recently a new method for determining the neutrino mass hierarchy by
comparing the effective values of the atmospheric \Delta m^2 measured in the
electron neutrino disappearance channel, \Delta m^2(ee), with the one measured
in the muon neutrino disappearance channel, \Delta m^2(\mu \mu), was proposed.
If \Delta m^2(ee) is larger (smaller) than \Delta m^2(\mu \mu) the hierarchy is
of the normal (inverted) type. We re-examine this proposition in the light of
two very high precision measurements: \Delta m^2(\mu \mu) that may be
accomplished by the phase II of the Tokai-to-Kamioka (T2K) experiment, for
example, and \Delta m^2(ee) that can be envisaged using the novel Mossbauer
enhanced resonant \bar\nu_e absorption technique. Under optimistic assumptions
for the systematic uncertainties of both measurements, we estimate the
parameter region of (\theta_13, \delta) in which the mass hierarchy can be
determined. If \theta_13 is relatively large, sin^2 2\theta_13 \gsim 0.05, and
both of \Delta m^2(ee) and \Delta m^2(\mu \mu) can be measured with the
precision of \sim 0.5 % it is possible to determine the neutrino mass hierarchy
at > 95% CL for 0.3 \pi \lsim \delta \lsim 1.7 \pi for the current best fit
values of all the other oscillation parameters.Comment: 12 pages, 6 postscript figure
Excitonic instability and electric-field-induced phase transition towards a two dimensional exciton condensate
We present an InAs-GaSb-based system in which the electric-field tunability
of its 2D energy gap implies a transition towards a thermodynamically stable
excitonic condensed phase. Detailed calculations show a 3 meV BCS-like gap
appearing in a second-order phase transition with electric field. We find this
transition to be very sharp, solely due to exchange interaction, and so, the
exciton binding energy is greatly renormalized even at small condensate
densities. This density gradually increases with external field, thus enabling
the direct probe of the Bose-Einstein to BCS crossover.Comment: LaTex, 11 pages, 3 ps figures, To appear in PR
Signature of Electronic Correlations in the Optical Conductivity of the Doped Semiconductor Si:P
Electronic transport in highly doped but still insulating silicon at low
temperatures is dominated by hopping between localized states; it serves as a
model system of a disordered solid for which the electronic interaction can be
investigated. We have studied the frequency-dependent conductivity of
phosphorus-doped silicon in the THz frequency range (30 GHz to 3 THz) at low
temperatures K. The crossover in the optical conductivity from a
linear to a quadratic frequency dependence as predicted by Efros and Shklovskii
is observed qualitatively; however, the simple model does not lead to a
quantitative agreement. Covering a large range of donor concentration, our
temperature- and frequency-dependent investigations reveal that electronic
correlation effects between the localized states play an important and complex
role at low temperatures. In particular we find a super-linear frequency
dependence of the conductivity that highlights the influence of the density of
states, i.e. the Coulomb gap, on the optical conductivity. When approaching the
metal-to-insulator transition by increasing doping concentration, the
dielectric constant and the localization length exhibit critical behavior.Comment: 9 pages, 8 figures, 1 tabl
Spin-Orbit Interactions in Bilayer Exciton-Condensate Ferromagnets
Bilayer electron-hole systems with unequal electron and hole densities are
expected to have exciton condensate ground states with spontaneous
spin-polarization in both conduction and valence bands. In the absence of
spin-orbit and electron-hole exchange interactions there is no coupling between
the spin-orientations in the two quantum wells. In this article we show that
Rashba spin-orbit interactions lead to unconventional magnetic anisotropies,
whose strength we estimate, and to ordered states with unusual quasiparticle
spectra.Comment: 36 pages, 12 figure
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