197 research outputs found
Circular photogalvanic effect induced by monopolar spin orientation in p-GaAs/AlGaAs MQW
The circular photogalvanic effect (CPGE) has been observed in (100)-oriented
-GaAs/AlGaAs quantum wells at normal incidence of far-infrared radiation. It
is shown that monopolar optical spin orientation of free carriers causes an
electric current which reverses its direction upon changing from left to right
circularly polarized radiation. CPGE at normal incidence and the occurence of
the linear photogalvanic effect indicate a reduced point symmetry of studied
multi-layered heterostructures. As proposed, CPGE can be utilized to
investigate separately spin polarization of electrons and holes and the
symmetry of quantum wells.Comment: 4 pages, 3 figure
Laterally pumped GaAs/AlGaAs quantum wells as sources of broadband terahertz radiation
In this work we consider lateral current pumped GaAs/AlGaAs quantum wells as sources of incoherent terahertz radiation. The lateral field heats the electrons in a two-dimensional quantum layer and increases the population of higher subbands, hence also increasing the radiation power generated in spontaneous intersubband emission processes. Digitally graded quasi-parabolic and simple square quantum wells are considered, and the advantages of both types are discussed. Calculations at lattice temperatures of 77 K and 300 K, for electric fields up to 10 kV/cm, show that the optical output power of ~100â200 W/m2 may be achieved for the 7 THz source. The main peak of the spectrum, at 7 THz, of the quasi-parabolic quantum well exceeds the black body radiation at 300 K by approximately a factor of two and by two orders of magnitude at 77 K
Optical Spin Orientation under Inter- and Intra-Subband Transitions in QWs
It is shown that absorption of circularly polarized infrared radiation
achieved by inter-subband and intra-subband (Drude-like) transitions results in
a monopolar spin orientation of free carriers. The monopolar spin polarization
in zinc-blende-based quantum wells (QWs) is demonstrated by the observation of
the spin-galvanic and circular photogalvanic effects. It is shown that
monopolar spin orientation in n-type QWs becomes possible if an admixture of
valence band states to the conduction band wave function and the spin-orbit
splitting of the valence band are taken into account
Monopolar Optical Orientation of Electronic Spins in Semiconductors
It is shown that absorption of circularly polarized infrared radiation due to
intraband (Drude-like) transitions in n-type bulk semiconductors and due to
intra-subband or inter-subband transitions in quantum well (QW) structures
results in a monopolar spin orientation of free electrons. Spin polarization in
zinc-blende-structure based QWs is demonstrated by the observation of the
spin-galvanic and the circular photogalvanic effects. The monopolar spin
orientation in n-type materials is shown to be possible if an admixture of
valence band states to the conduction band wave function and the spin-orbit
splitting of the valence band are taken into account
Spin sensitive bleaching and monopolar spin orientation in quantum wells
Spin sensitive bleaching of the absorption of far-infrared radiation has been
observed in -type GaAs/AlGaAs quantum well structures. The absorption of
circularly polarized radiation saturates at lower intensities than that of
linearly polarized light due to monopolar spin orientation in the first heavy
hole subband. Spin relaxation times of holes in -type material in the range
of tens of ps were derived from the intensity dependence of the absorption.Comment: Figures have been updated due to technical printing problems
(Postscript mismatch
Mass measurements of very neutron-deficient Mo and Tc isotopes and their impact on rp process nucleosynthesis
The masses of ten proton-rich nuclides, including the N=Z+1 nuclides 85-Mo
and 87-Tc, were measured with the Penning trap mass spectrometer SHIPTRAP.
Compared to the Atomic Mass Evaluation 2003 a systematic shift of the mass
surface by up to 1.6 MeV is observed causing significant abundance changes of
the ashes of astrophysical X-ray bursts. Surprisingly low alpha-separation
energies for neutron-deficient Mo and Tc are found, making the formation of a
ZrNb cycle in the rp process possible. Such a cycle would impose an upper
temperature limit for the synthesis of elements beyond Nb in the rp process.Comment: Link to online abstract:
http://link.aps.org/doi/10.1103/PhysRevLett.106.12250
Present and Future Experiments with Stored Exotic Nuclei at Relativistic Energies
Recent progress is presented from experiments on masses and lifetimes of bare
and few-electron exotic nuclei at GSI.Comment: Proceedings of International Conference on "Frontiers in Nuclear
Structure, Astrophysics and Reactions", Kos, Greece, September 12-17, 200
Impurity breakdown and terahertz luminescence in n-GaN epilayers under external electric field
We report on the observation and experimental studies of impurity breakdown and terahertz luminescence in n-GaN epilayers under external electric field. The terahertz electroluminescence is observed in a wide range of doping levels (at noncompensated donor density from 4.5Ă10[sup 16] to 3.4Ă10[sup 18]âcm[sup â3]). Spectra of terahertz luminescence and photoconductivity are studied by means of Fourier transform spectrometry. Distinctive features of the spectra can be assigned to intracenter electron transitions between excited and ground states of silicon and oxygen donors and to hot electron transitions to the donor states.Peer reviewe
Continuous dielectric permittivity II: An Iterative Method for Calculating the Polar Component of the Molecular Solvation Gibbs Energy Under a Smooth Change in the Dielectric Permittivity of a Solution
An iterative method for calculating the polar component of the solvation
Gibbs energy under a smooth change in dielectric permittivity, both between a
substrate and a solvent and in a solvent is formulated on the basis of a
previously developed model. The method is developed in the approximation of the
local relationship D = \eps (r) E between the displacement vectors D and the
electric field intensity E.Comment: 36 pages,3 Figures, in English and in Russia
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