35 research outputs found
Binding Energy of Charged Excitons in ZnSe-based Quantum Wells
Excitons and charged excitons (trions) are investigated in ZnSe-based quantum
well structures with (Zn,Be,Mg)Se and (Zn,Mg)(S,Se) barriers by means of
magneto-optical spectroscopy. Binding energies of negatively () and positively
(X+) charged excitons are measured as functions of quantum well width, free
carrier density and in external magnetic fields up to 47 T. The binding energy
of shows a strong increase from 1.4 to 8.9 meV with decreasing quantum well
width from 190 to 29 A. The binding energies of X+ are about 25% smaller than
the binding energy in the same structures. The magnetic field behavior of and
X+ binding energies differ qualitatively. With growing magnetic field strength,
increases its binding energy by 35-150%, while for X+ it decreases by 25%.
Zeeman spin splittings and oscillator strengths of excitons and trions are
measured and discussed
Absorption spectrum of a weakly n-doped semiconductor quantum well
We calculate, as a function of temperature and conduction band electron
density, the optical absorption of a weakly n-doped, idealized semiconductor
quantum well. In particular, we focus on the absorption band due to the
formation of a charged exciton. We conceptualize the charged exciton as an
itinerant excitation intimately linked to the dynamical response of itinerant
conduction band electrons to the appearance of the photo-generated valence band
hole. Numerical results for the absorption in the vicinity of the exciton line
are presented and the spectral weights associated with, respectively, the
charged exciton band and the exciton line are analyzed in detail. We find, in
qualitative agreement with experimental data, that the spectral weight of the
charged exciton grows with increasing conduction band electron density and/or
decreasing temperature at the expense of the exciton.Comment: 5 pages, 4 figure
Search for rare Phi decays in pi+ pi_ gamma final state
A search for phi radiative decays has been performed using a data sample of
about 2.0 million phi decays collected by the CMD-2 detector at VEPP-2M
collider in Novosibirsk. From the selected e+ e- -> pi+ pi- gamma events the
following results were obtained: B(phi -> f0(980) gamma) < 1x10-4 for
destructive and B(phi -> f0(980) gamma) < 7x10-4 for constructive interference
with the Bremsstrahlung process respectively, B(phi -> gamma -> pi+ pi- gamma)
20 MeV, B(phi -> rho gamma) < 7x10-4. From the
selected e+ e- -> mu+ mu- gamma events B(phi -> mu+ mu- gamma) =
(2.3+-1.0)x10-5 has been obtained for E of gamma> 20 MeV. The upper limit on
the P,CP-violating decay eta -> pi+ pi- has also been placed: B(eta -> pi+ pi-)
< 9x10-4 . All upper limits are at 90 % C.L.Comment: 18 pages, 7 figure
Single picojoule pulse switching of magnetization in ferromagnetic (Ga,Mn)As
Contains fulltext :
84030.pdf (publisher's version ) (Open Access)3 p
Observation of giant magnetic linear dichroism in (Ga,Mn)As
Contains fulltext :
32798.pdf (publisher's version ) (Open Access
Identification of acoustically induced spin resonances of Si vacancy centers in 4H-SiC
Silicon vacancies () in the 4H polytype of SiC form color centers with long-lived and optically addressable spin states, which make them promising spin qubits for quantum communication and sensing. These centers can be created both in the cubic () and in the hexagonal () local crystallographic environments of the 4H-SiC host. While the center can be efficiently manipulated by optically detected magnetic resonance (ODMR) even at room temperature, ODMR control of the centers could so far only been achieved at cryogenic temperatures. Here, we show that magnetic resonance induced by the dynamic strain of a surface acoustic wave can overcome this limitation and enable the efficient manipulation of centers up to room temperatures. Based on the width and temperature dependence of the acoustically induced spin resonances, we attribute them to spin transitions between the and spin sublevels of the excited state of the centers. These results are an important step towards on-chip quantum information processing based on centers driven by acoustic fields
Acoustically Induced Spin Resonances of Silicon-Vacancy Centers in <math display="inline" overflow="scroll"><mn>4</mn><mi>H</mi></math>-SiC
International audienceThe long-lived and optically addressable spin states of silicon vacancies (VSi) in 4H-SiC make them promising qubits for quantum communication and sensing. These color centers can be created in both the hexagonal (V1) and in the cubic (V2) local crystallographic environments of the 4H-SiC host. While the spin of the V2 center can be efficiently manipulated by optically detected magnetic resonance at room temperature, spin control of the V1 center above cryogenic temperatures has so far remained elusive. Here, we show that the dynamic strain of surface acoustic waves can overcome this limitation and efficiently excite magnetic resonances of V1 centers up to room temperature. Based on the width and temperature dependence of the acoustically induced spin resonances of the V1 centers, we attribute them to transitions between spin sublevels in the excited state. The acoustic spin control of both kinds of VSi centers in their excited states opens alternative ways for applications in quantum technologies based on spin optomechanics
Picosecond dynamics of the photoinduced spin polarization in epitaxial (Ga,Mn)as films.
Contains fulltext :
57451.pdf (publisher's version ) (Open Access)Static and time-resolved magneto-optical spectra of the ferromagnetic semiconductor (Ga,Mn)As show that a pulsed photoexcitation with a fluence of 10 microJ/cm(2) is equivalent to the application of an external magnetic field of about 1 mT, which relaxes with a decay time of 30 ps. This relaxation is attributed to the spin relaxation of electrons in the conduction band and is found to be not affected by interactions with Mn ions
Radiative corrections for pion and kaon production at e+ e- colliders of energies below 2-GeV
Processes of electron-positron annihilation into charged pions and kaons are considered. Radiative corrections are taken into account exactly in the first order and within the leading logarithmic approximation in higher orders. A combined approach for accounting exact calculations and electron structure functions is used. An accuracy of the calculation can be estimated about 0.2%
Magnetization manipulation in (Ga,Mn)As by subpicosecond optical excitation
Contains fulltext :
32698.pdf (publisher's version ) (Open Access