3,220 research outputs found
Constraining the range of Yukawa gravity interaction from S2 star orbits III: improvement expectations for graviton mass bounds
Recently, the LIGO-Virgo collaboration discovered gravitational waves and in
their first publication on the subject the authors also presented a graviton
mass constraint as eV (Abbott et al., 2016).
In the paper we analyze a potential to reduce upper bounds for graviton mass
with future observational data on trajectories of bright stars near the
Galactic Center. Since gravitational potentials are different for these two
cases, expressions for relativistic advance for general relativity and Yukawa
potential are different functions on eccentricity and semimajor axis, it gives
an opportunity to improve current estimates of graviton mass with future
observational facilities. In our considerations of an improvement potential for
a graviton mass estimate we adopt a conservative strategy and assume that
trajectories of bright stars and their apocenter advance will be described with
general relativity expressions and it gives opportunities to improve graviton
mass constraints. In contrast with our previous studies, where we present
current constraints on parameters of Yukawa gravity (Borka et al., 2013) and
graviton mass (Zakharov et al., 2016) from observations of S2 star, in the
paper we express expectations to improve current constraints for graviton mass,
assuming the GR predictions about apocenter shifts will be confirmed with
future observations. We concluded that if future observations of bright star
orbits during around fifty years will confirm GR predictions about apocenter
shifts of bright star orbits it give an opportunity to constrain a graviton
mass at a level around eV or slightly better than current
estimates obtained with LIGO observations.Comment: 16 pages, 1 Figure, 1 Table, corrected minor typo
Dilute magnetic semiconductor quantum-well structures for magnetic field tunable far-infrared/terahertz absorption
The design of ZnCdSe–ZnMnSe-based quantum
wells is considered, in order to obtain a large shift of the peak absorption wavelength in the far infrared range, due to a giant Zeeman splitting with magnetic field, while maintaining a reasonably large value of peak absorption. A triple quantum-well structure with a suitable choice of parameters has been found to satisfy such requirements. A maximal tuning range between 14.6 and 34.7 meV is obtained, when the magnetic field varies from zero
to 5 T, so the wavelength of the absorbed radiation decreases from 85.2 to 35.7 μm with absorption up to 1.25% at low temperatures. These structures might form the basis for magnetic field tunable photodetectors and quantum cascade lasers in the terahertz range
Magnetoresistance and Hall effect in e-doped superconducting SrLaCuO thin films
We have epitaxially grown c-axis oriented SrxLa1-xCuO2 thin films by rf
sputtering on KTaO3 substrates with x = 0.12. The as-grown deposits are
insulating and a series of superconducting films with various Tc(R=0) up to 26
K have been obtained by in-situ oxygen reduction. Transport measurements in the
ab plane of these samples have been undertaken. We report original results on
the temperature dependence of the Hall effect and on the anisotropic
magnetoresistance (T > Tc). We discuss the magnitude of upper critical fields
and anisotropy, the Hall effect, which presents changes of sign indicative of
the existence of two types of carriers, the normal state magnetoresistance,
negative in parallel magnetic field, a possible signature of spin scattering.
These properties are compared to those of hole-doped cuprates, such as
BiSr(La)CuO with comparable Tc.Comment: 4 pages, 4 figures; to appear in Proceedings of LT25, Journal of
Physics : Conference Serie
Optically pumped terahertz laser based on intersubband transitions in a GaN/AlGaN double quantum well
A design for a GaN/AlGaN optically pumped terahertz laser emitting at 34 µm (ΔE~36 meV) is presented. This laser uses a simple three-level scheme where the depopulation of the lower laser level is achieved via resonant longitudinal-optical-phonon emission. The quasibound energies and associated wave functions are calculated with the intrinsic electric field induced by the piezoelectric and the spontaneous polarizations. The structures based on a double quantum well were simulated and the output characteristics extracted using a fully self-consistent rate equation model with all relevant scattering processes included. Both electron-longitudinal-optical phonon and electron-acoustic-phonon interactions were taken into account. The carrier distribution in subbands was assumed to be Fermi–Dirac-like, with electron temperature equal to the lattice temperature, but with different Fermi levels for each subband. A population inversion of 12% for a pumping flux Φ=10(27) cm(–2) s(–1) at room temperature was calculated for the optimized structure. By comparing the calculated modal gain and estimated waveguide and mirror losses the feasibility of laser action up to room temperature is predicted
Designing strain-balanced GaN/AlGaN quantum well structures: Application to intersubband devices at 1.3 and 1.55 mu m wavelengths
A criterion for strain balancing of wurtzite group-III nitride-based multilayer heterostructures is presented. Single and double strain-balanced GaN/AlGaN quantum well structures are considered with regard to their potential application in optoelectronic devices working at communication wavelengths. The results for realizable, strain-balanced structures are presented in the form of design diagrams that give both the intersubband transition energies and the dipole matrix elements in terms of the structural parameters. The optimal parameters for structures operating at lambda ~1.3 and 1.55 µm were extracted and a basic proposal is given for a three level intersubband laser system emitting at 1.55µm and depopulating via resonant longitudinal optical(LO)phonons (h omega(LO)approximate to 90 meV). © 2003 American Institute of Physics
Penetration depth of electron-doped-infinite-layer SrLaCuO thin films
The in-plane penetration depth of SrLaCuO thin
films at various doping obtained from oxygen reduction has been measured, using
AC susceptibility measurements. For the higher doping samples, the superfluid
density deviates strongly from the s-wave behavior, suggesting, in analogy with
other electron-doped cuprates, a contribution from a nodal hole pocket, or a
small gap on the Fermi surface such as an anisotropic s-wave order parameter.
The low value of the superfluid densities, likely due to a strong
doping-induced disorder, places the superconducting transition of our samples
in the phase-fluctuation regime
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