6,423 research outputs found
Observation of hypersonic phononic crystal effects in porous silicon superlattices
Brillouin light scattering experiments were carried out on porous silicon superlattices with modulation wavelengths in the range 37–167 nm. Phonon frequencies deduced from the Brillouin spectra show good agreement with those obtained from an elastic continuum model for a system with one-dimensional periodicity. Evidence for the existence of a hypersonic phononic bandgap and zone-folded longitudinal acoustic phonons is reported
Lepton polarization correlations in
In this work we will study the polarizations of both leptons () in the
decay channel . In the case of the dileptonic inclusive
decay , where apart from the polarization asymmetries
of single lepton , one can also observe the polarization asymmetries of
both leptons simultaneously. If this sort of measurement is possible then we
can have, apart from decay rate, FB asymmetry and the six single lepton
polarization asymmetries (three each for and ), nine more
double polarization asymmetries. This will give us a very useful tool in more
strict testing of SM and the physics beyond. We discuss the double polarization
asymmetries of leptons in the decay mode within
the SM and the Minimal Supersymmetric extensions of it.Comment: 21 pages, 21 figures; version to match paper to appear in PR
B_s ---> \gamma \gamma decay in the model III and 3HDM(O_2) with CP violating effects
We analyse the CP asymmetry for B_{s} -->\gamma\gamma in the two Higgs
doublet model with tree level flavor changing currents (model III) and three
Higgs doublet model with O_2 symmetry in the Higgs sector, including O_{7} type
long distance effects. Further, we study the dependencies of the branching
ratio Br(B_{s} --> \gamma\gamma)$ and the ratio of CP-even and CP-odd amplitude
squares, R=|A^{+}|^2/|A^{-}|^2, on the CP parameter sin \theta. We found that,
there is a weak CP asymmetry, at the order of 10^{-4}. Besides, the branching
ratio Br(B_{s} --> \gamma\gamma), and also R ratio, is not sensitive to the CP
parameter for |\frac{\bar{\xi}^{U}_{N,tt}}{\bar{\xi}^{D}_{N,bb}}|<1.Comment: 17 pages, 11 figure
Electronic spectra of polyatomic molecules with resolved individual rotational transitions
The density of rotational transitions for a polyatomic molecule is so large that in general many such
transitions are hidden under the Doppler profile, this being a fundamental limit of conventional high
resolution electronic spectroscopy. We present here the first Doppler-free cw two-photon spectrum of a
polyatomic molecule. In the case of benzene, 400 lines are observed of which 300 are due to single rotational
transitions, their spacing being weil below the Doppler profile. The resolution so achieved is 1.5 X 10'.
Benzene is a prototype planar molecule taken to have D •• symmetry in the ground as weil as in the first
excited state. From our ultra-high resolution results it is found that benzene in the excited SI state i8 a
symmetrical rotor to a high degree. A negative inertial defect is found for the excited state. The origin of this
inertial defect is discused
CP violation in polarized B-> pi ell+ ell- and B-> rho ell+ ell- decays
We study the decay rate and the CP violating asymmetry of the exclusive B->
pi ell+ ell- and B-> rho ell+ ell- decays in the case where one of the final
leptons is polarized. We calculate the contributions coming from the individual
polarization states in order to identify a so-called wrong sign decay, which is
a decay with a given polarization, whose width and CP asymmetry are smaller as
compared to the unpolarized one. The results are presented for electron and tau
leptons. We observe that in particular decay channels, one can identify a wrong
sign decay which is more sensitive to new physics beyond the Standard Model.Comment: 24 pages, 10 figures; minor errors and misprints corrected,
references added, version to be published in EPJ
New physics effects to the lepton polarizations in the B -> K l^+ l^- decay
Using the general, model independent form of the effective Hamiltonian, the
general expressions of the longitudinal, normal and transversal polarization
asymmetries for (l^-) and (l^+) and combinations of them for the exclusive (B
-> K l^+ l^-) decay are found. The sensitivity of lepton polarizations and
their combinations on new Wilson coefficients are studied. It is found that
there exist regions of Wilson coefficients for which the branching ratio
coincides with the Standard Model result while the lepton polarizations differ
substantially from the standard model prediction. Hence, studying lepton
polarization in these regions of new Wilson coefficients can serve as a
promising tool for establishing new physics beyond the Standard Model.Comment: 18 pp, 14 figures (postscript formatted), LaTex formatte
Band edge noise spectroscopy of a magnetic tunnel junction
We propose a conceptually new way to gather information on the electron bands
of buried metal(semiconductor)/insulator interfaces. The bias dependence of low
frequency noise in FeV/MgO/Fe (0 x 0.25) tunnel junctions
show clear anomalies at specific applied voltages, reflecting electron
tunneling to the band edges of the magnetic electrodes. The change in magnitude
of these noise anomalies with the magnetic state allows evaluating the degree
of spin mixing between the spin polarized bands at the ferromagnet/insulator
interface. Our results are in qualitative agreement with numerical
calculations
Magnetic state dependent transient lateral photovoltaic effect in patterned ferromagnetic metal-oxide-semiconductor films
We investigate the influence of an external magnetic field on the magnitude
and dephasing of the transient lateral photovoltaic effect (T-LPE) in
lithographically patterned Co lines of widths of a few microns grown over
naturally passivated p-type Si(100). The T-LPE peak-to-peak magnitude and
dephasing, measured by lock-in or through the characteristic time of laser OFF
exponential relaxation, exhibit a notable influence of the magnetization
direction of the ferromagnetic overlayer. We show experimentally and by
numerical simulations that the T-LPE magnitude is determined by the Co
anisotropic magnetoresistance. On the other hand, the magnetic field dependence
of the dephasing could be described by the influence of the Lorentz force
acting perpendiculary to both the Co magnetization and the photocarrier drift
directions. Our findings could stimulate the development of fast position
sensitive detectors with magnetically tuned magnitude and phase responses
Detection of spin torque magnetization dynamics through low frequency noise
We present a comparative study of high frequency dynamics and low frequency
noise in elliptical magnetic tunnel junctions with lateral dimensions under 100
nm presenting current-switching phenomena. The analysis of the high frequency
oscillation modes with respect to the current reveals the onset of a
steady-state precession regime for negative bias currents above , when the magnetic field is applied along the easy axis of
magnetization. By the study of low frequency noise for the same samples, we
demonstrate the direct link between changes in the oscillation modes with the
applied current and the normalised low frequency (1/f) noise as a function of
the bias current. These findings prove that low frequency noise studies could
be a simple and powerful technique to investigate spin-torque based
magnetization dynamics
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