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ABSTRACT: This paper reports on a study of the exciton polariton region in reflection spectra of wide CdTe/CdZnTe quantum wells (with
well width exceeding by far the exciton Bohr radius) measured in Voigt geometry in a magnetic field. In a magnetic field,
forbidden exciton lines were observed to appear for each exciton quantization level. The exciton diamagnetic shift constant
has been observed to decrease noticeably with increasing number of the quantum confined level. A comparison of calculated
with experimental spectra reveals a growth of the exciton translational mass with increasing magnetic field. It has been shown
that both the growth of mass and the decrease of the diamagnetic shift can be traced to mixing of exciton internal with translational
motion states.
Physics of the Solid State 04/2012; 51(8):1649-1655. · 0.71 Impact Factor
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W. Pacuski,
J. Suffczyński,
P. Osewski,
P. Kossacki,
A. Golnik,
J. A. Gaj,
C. Deparis,
C. Morhain,
E. Chikoidze,
Y. Dumont,
D. Ferrand, J. Cibert,
T. Dietl
[show abstract]
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ABSTRACT: This work presents results of near-band gap magnetooptical studies on Zn1−xMnxO epitaxial layers. We observe excitonic transitions in reflectivity and photoluminescence that shift toward higher energies when the Mn concentration increases and split nonlinearly under the magnetic field. Excitonic shifts are determined by the s,p−d exchange coupling to magnetic ions, by the electron-hole s−p exchange, and the spin-orbit interactions. A quantitative description of the magnetoreflectivity findings indicates that the free excitons A and B are associated with the Γ7 and Γ9 valence bands, respectively, the order reversed as compared to wurtzite GaN. Furthermore, our results show that the magnitude of the giant exciton splittings, specific to dilute magnetic semiconductors, is unusual: the magnetoreflectivity data are described by an effective exchange energy N0(β(app)−α(app))=+0.2±0.1 eV, which points to small and positive N0β(app). It is shown that both the increase of the gap with x and the small positive value of the exchange energy N0β(app) corroborate recent theory describing the exchange splitting of the valence band in a nonperturbative way, suitable for the case of a strong p−d hybridization.
Phys. Rev. B. 07/2011; 84(3).
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W. Pacuski,
J. Suffczynski,
P. Osewski,
P. Kossacki,
A. Golnik,
J. A. Gaj,
C. Deparis,
C. Morhain,
E. Chikoidze,
Y. Dumont,
D. Ferrand, J. Cibert,
T. Dietl
[show abstract]
[hide abstract]
ABSTRACT: This work presents results of near-band gap magnetooptical studies on
(Zn,Mn)O epitaxial layers. We observe excitonic transitions in reflectivity and
photoluminescence, that shift towards higher energies when the Mn concentration
increases and split nonlinearly under the magnetic field. Excitonic shifts are
determined by the s,p-d exchange coupling to magnetic ions, by the
electron-hole s-p exchange, and the spin-orbit interactions. A quantitative
description of the magnetoreflectivity findings indicates that the free
excitons A and B are associated with the Gamma_7 and Gamma_9 valence bands,
respectively, the order reversed as compared to wurtzite GaN. Furthermore, our
results show that the magnitude of the giant exciton splittings, specific to
dilute magnetic semiconductors, is unusual: the magnetoreflectivity data is
described by an effective exchange energy N_0(beta-alpha)=+0.2+/-0.1 eV, what
points to small and positive N_0 beta. It is shown that both the increase of
the gap with x and the small positive value of the exchange energy N_0 beta
corroborate recent theory describing the exchange splitting of the valence band
in a non-perturbative way, suitable for the case of a strong p-d hybridization.
05/2011;
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ABSTRACT: An optical spin orientation is achieved for a Mn atom localized in a semiconductor quantum dot using quasiresonant excitation at zero magnetic field. Optically created spin polarized carriers generate an energy splitting of the Mn spin and enable magnetic moment orientation controlled by the photon helicity and energy.The dynamics and the magnetic field dependence of the optical pumping mechanism shows that the spin lifetime of an isolated Mn atom at zero magnetic field is controlled by a magnetic anisotropy induced by the built-in strain in the quantum dots. Relaxation times exceeding the micro-second range are measured (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 03/2010; 7(6):1651 - 1654.
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ABSTRACT: We demonstrate a high degree of an optical spin preparation of a single Mn atom embedded in a CdTe/ZnTe quantum dot (QD). Due to the strong exchange interaction of the manganese atom with an exciton injected into the QD the spin orientation can be achieved by quasi-resonant or fully-resonant optical creation of the polarized electron-hole pairs. A measured spin memory of the isolated Mn atom, in most of the cases, is in the microsecond range, and depends on the built-in strain in the quantum dot. During the resonant optical pumping process exciton spin-flip can occur without a change of the Mn spin providing a way to directly read the dynamics of the pumped spin state. The manganese spin orientation is achieved in a few tens of ns.
Journal of Physics Conference Series 03/2010; 210(1):012038.
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J. J. Davies,
L. C. Smith,
D. Wolverson,
V. P. Kochereshko, J. Cibert,
H. Mariette,
H. Boukari,
M. Wiater,
G. Karczewski,
T. Wojtowicz,
A. Gust,
C. Kruse,
D. Hommel
[show abstract]
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ABSTRACT: We have shown recently that the magnetic properties of excitons change significantly as the excitons acquire kinetic energy. In particular, the exciton magnetic moments are enhanced considerably, whilst the diamagnetism decreases. The behaviour can be investigated through spectroscopic studies of excitons confined in quantum wells of large width (greater than five times the exciton Bohr radius) and these motion-induced changes in the magnetic properties have now been observed for CdTe, ZnSe, ZnTe and GaAs. The present paper summarises these phenomena, with particular focus on CdTe and ZnSe, and shows that the changes can be accounted for by motion-induced mixing between the exciton ground and higher lying states. The mixing is caused by the gamma3 term in the Luttinger Hamiltonian which describes the dispersion curves for the valence band and, as a result, the form of the exciton wavefunction becomes motion-dependent. For both materials, excellent agreement is obtained between experiment and the results predicted by this mechanism.
physica status solidi (b). 01/2010; 9999:NA.
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ABSTRACT: An optical spin orientation is achieved for a Mn atom localized in a semiconductor quantum dot using quasiresonant excitation at zero magnetic field. Optically created spin-polarized carriers generate an energy splitting of the Mn spin and enable magnetic moment orientation controlled by the photon helicity and energy. The dynamics and the magnetic field dependence of the optical pumping mechanism show that the spin lifetime of an isolated Mn atom at zero magnetic field is controlled by a magnetic anisotropy induced by the built-in strain in the quantum dots.
Physical Review Letters 04/2009; 102(12):127402. · 7.37 Impact Factor
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M Goryca,
D Ferrand,
P Kossacki,
M Nawrocki,
W Pacuski,
W Maślana,
J A Gaj,
S Tatarenko, J Cibert,
T Wojtowicz,
G Karczewski
[show abstract]
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ABSTRACT: The evolution of the magnetization in (Cd,Mn)Te quantum wells after a short pulse of magnetic field was determined from the giant Zeeman shift of spectroscopic lines. The dynamics in the absence of a static magnetic field was found to be up to 3 orders of magnitude faster than that at 1 T. Hyperfine interaction and strain are mainly responsible for the fast decay. The influence of a hole gas is clearly visible: at zero field anisotropic holes stabilize the system of Mn ions, while in a magnetic field of 1 T they are known to speed up the decay by opening an additional relaxation channel.
Physical Review Letters 02/2009; 102(4):046408. · 7.37 Impact Factor
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[show abstract]
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ABSTRACT: A hight degree of spin polarization is achieved for a Mn atom localized in a
semiconductor quantum dot using quasi-resonant optical excitation at zero
magnetic field. Optically created spin polarized carriers generate an energy
splitting of the Mn spin and enable magnetic moment orientation controlled by
the photon helicity and energy. The dynamics and the magnetic field dependence
of the optical pumping mechanism shows that the spin lifetime of an isolated Mn
atom at zero magnetic field is controlled by a magnetic anisotropy induced by
the built-in strain in the quantum dots.
12/2008;
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ABSTRACT: This paper overviews our recent results on the magneto-optics of excitons in wide quantum wells, when the well width is much larger than the exciton Bohr radius. We have demonstrated that the magnetic moment of the exciton increases by an order of magnitude due to its motion along the magnetic field. The effect was observed for a set of quantum well structures with different well widths and based on various semiconductor compounds. The reason for this effect is mixing of the exciton's center-of-mass motion and the internal motion of electron and hole in the exciton.
Semiconductor Science and Technology 10/2008; 23(11):114011. · 1.72 Impact Factor
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V. P. Kochereshko,
L. C. Smith,
J. J. Davies,
R. T. Cox,
A. Platonov,
D. Wolverson,
H. Boukari,
H. Mariette, J. Cibert,
M. Wiater,
T. Wojtowicz,
G. Karczewski
[show abstract]
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ABSTRACT: We have observed remarkable changes in the magnetic properties of excitons as they acquire kinetic energy. In particular, the Zeeman splittings and diamagnetic shifts of excitonic transitions when magnetic fields are applied along the growth direction of (001) wide quantum wells of CdTe, ZnSe, ZnTe and GaAs are found to to have a strong dependence on the translational wavevector Kz. The behaviour of the Zee-man splittings corresponds to enhancement of the magnetic moments of the excitons. This enhancement is particularly marked when their translational kinetic energy becomes comparable with the exciton Rydberg and can be described by what appears to be a universal function of Kz. A model for the behaviour is outlined which involves motionally-induced mixing between the 1S hydrogenic exciton ground state and excited nP states. The observations imply that there are significant changes in the structure of the exciton as its translational kinetic energy increases. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (b) 05/2008; 245(6):1059 - 1063. · 1.32 Impact Factor
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W Pacuski,
P Kossacki,
D Ferrand,
A Golnik, J Cibert,
M Wegscheider,
A Navarro-Quezada,
A Bonanni,
M Kiecana,
M Sawicki,
T Dietl
[show abstract]
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ABSTRACT: The giant Zeeman splitting of free excitons is measured in Ga(1-x)Fe(x)N. Magneto-optical and magnetization data imply the ferromagnetic sign and a reduced magnitude of the effective p-d exchange energy governing the interaction between Fe(3+) ions and holes in GaN, N_{0}beta(app)=+0.5+/-0.2 eV. This finding corroborates the recent suggestion that the strong p-d hybridization specific to nitrides and oxides leads to significant renormalization of the valence band exchange splitting.
Physical Review Letters 02/2008; 100(3):037204. · 7.37 Impact Factor
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J. J. Davies,
L. C. Smith,
D. Wolverson,
H. Boukari,
R. T. Cox,
H. Mariette, J. Cibert,
V. P. Kochereshko,
A. Platonov,
M. Wiater,
T. Wojtowicz,
G. Karczewski
[show abstract]
[hide abstract]
ABSTRACT: We report remarkable changes in the magnetic properties of excitons as they acquire kinetic energy in wide (001) quantum wells of CdTe, ZnSe, ZnTe and GaAs. In particular, the magnetic moments (g-values) when magnetic fields are applied in the growth direction are shown to. have a strong dependence on the translational wavevector K-z. The dependence is particularly marked when Kz is of the order of the inverse of the exciton Bohr radius or, equivalently, when the translational kinetic energy becomes comparable with the exciton Rydberg. The behaviour is ascribed to motionally-induced mixing between the 1S hydrogenic exciton ground state and excited nP states and is describable by what appears to be a universal formula.
Journal- Korean Physical Society 01/2008; 53(5):2803-2807. · 0.45 Impact Factor
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L. C. Smith,
J. J. Davies,
D. Wolverson,
S. Crampin,
R. T. Cox, J. Cibert,
H. Mariette,
V. P. Kochereshko,
M. Wiater,
G. Karczewski,
T. Wojtowicz
Physical Review B. 01/2008; 78(8).
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W. Pacuski,
P. Kossacki,
D. Ferrand,
A. Golnik, J. Cibert,
M. Wegscheider,
A. Navarro-Quezada,
A. Bonanni,
M. Kiecana,
M. Sawicki,
T. Dietl
[show abstract]
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ABSTRACT: A direct observation of the giant Zeeman splitting of the free excitons in (Ga,Fe)N is reported. The magnetooptical and magnetization data imply the ferromagnetic sign and a reduced magnitude of the effective p-d exchange energy governing the interaction between Fe^{3+} ions and holes in GaN, N_0 beta^(app) = +0.5 +/- 0.2 eV. This finding corroborates the recent suggestion that the strong p-d hybridization specific to nitrides and oxides leads to significant renormalization of the valence band exchange splitting.
09/2007;
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ABSTRACT: We report on the intrinsic ferromagnetic properties of wurtzite Ga0.937Mn0.063N diluted magnetic semiconductor grown by plasma‐assisted molecular beam epitaxy. The growth conditions were carefully optimized to obtain single phase (Ga,Mn)N samples. The high structural quality is confirmed by x‐ray diffraction experiments. Ferromagnetism is unambiguously demonstrated by both macroscopic magnetization measurements and x‐ray magnetic circular dichroism spectra recorded at the Mn K‐edge. The Curie temperature is found ≈8 K with a spontaneous magnetic moment of 2.4 μB per Mn at 2 K. © 2007 American Institute of Physics
AIP Conference Proceedings. 04/2007; 893(1):1173-1174.
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ABSTRACT: We describe a direct observation of the excitonic giant Zeeman splitting in Ga1−xMnxN, a wide-gap III-V diluted magnetic semiconductor. Reflectivity and absorption spectra measured at low temperatures display the A and B excitons, with a shift under magnetic field due to s,p-d exchange interactions. Using an excitonic model, we determine the difference of exchange integrals between Mn3+ and free carriers in GaN, N0(α−β)=−1.2±0.2 eV. Assuming a reasonable value of α, this implies a positive sign of β which corresponds to a rarely observed ferromagnetic interaction between the magnetic ions and the holes involved in the transition.
Phys. Rev. B. 04/2007; 76(16).
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ABSTRACT: The relaxation of the magnetization after a short pulse of magnetic field in n-doped and p-doped (Cd,Mn)Te quantum wells is determined from the giant Zeeman shift of the photoluminescence and transmission lines. This technique allows us to investigate the magnetization dynamics in zero field. In n-doped samples the magnetization relaxation is found to be faster than 20 ns. In case of p-doped samples two components of relaxation are observed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 02/2007; 4(2):307 - 310.
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ABSTRACT: We want to review recent structural investigations of the heteroepitaxial interfaces between II-VI semiconductors deposited by Molecular Beam Epitaxy and GaAs substrates. The structure of the relaxed interfaces will firstly be dealt with by reference to High Resolution Microscopy results. The second part will mainly focus on the way growth proceeds in its early stages as determined from diverse investigations involving very thin deposits.
Physica Scripta 01/2007; 1991(T35):268. · 1.20 Impact Factor
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S. Marcet,
W. Pacuski,
E. Sarigiannidou,
F. Wilhelm,
D. Ferrand,
S. Kuroda,
R. M. Galera,
E. Gheeraert, J. Cibert,
A. Rogalev,
H. Mariette,
P. Kossacki
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ABSTRACT: (Ga,Mn)N epilayers with a low Mn content have been investigated by magneto-optical spectroscopy. Absorption bands at 1.41 eV allow us to study the nature of the valence and spin state of Mn. An estimation of the exchange integrals is given through the observation of the excitons A and B near the energy gap. For Mn content higher than 2%, magnetization measurements supported by X-ray magnetic circular dichroism, show ferromagnetic properties with a Curie temperature TC≈8 K for 6.3% Mn. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 01/2007; 3(12):4062 - 4065.
