Dependence of crystal field splitting of 5d levels on hosts in the halide crystals

The crystal field splitting of 5d level of EU2+ and Ce3+ in halide crystals has been studied. Our results indicate that the 10Dq splitting can be directly related to the homopolar part of average energy gap, the coordination number of central (doped) ion, the charge of neighboring anions and bond ionicity between central ion to nearest anions. A relation between the 10Dq splitting and the above mentioned factors is presented. Our calculated results are in reasonable agreement with diverse experiments.

Crystal field splitting of Nd3+ ion and chemical bonds on the host crystals

In terms of the theory of chemical bonds on complex crystals(CBCC), the crystal structure and coordination, the chemical bond parameters of a group of ABO(4)-type crystals were calculated in detail, The results show that the relation between the crystal field splitting of Nd3+ ion and the covalency of the crystal is linear.

Electric-field switching of exciton spin splitting in coupled quantum dots

We investigate theoretically the spin splitting of the exciton states in semiconductor coupled quantum dots (CQDs) containing a single magnetic ion. We find that the spin splitting can be switched on/off in the CQDs via the sp-d exchange interaction using the electric field. An interesting bright-to-dark exciton transition can be found and it significantly affects the photoluminescence spectrum. This phenomenon is induced by the transition of the ground exciton state, arising from the hole mixing effect, between the bonding and antibonding states. (C) 2008 American Institute of Physics.

Electric Field Control of Interface Related Spin Splitting in Step Quantum Wells

Spin splitting of the AlyGa1-yAs/GaAs/AlxGa1-xAs/AlyGa1-yAs (x not equal y) step quantum wells (QWs) has been theoretically investigated with a model that includes both the interface and the external electric field contribution. The overall spin splitting is mainly determined by the interface contribution, which can be well manipulated by the external electric field. In the absence of the electric field, the Rashba effect exists due to the internal structure inversion asymmetry (SIA). The electric field can strengthen or suppress the internal SIA, resulting in an increase or decrease of the spin splitting. The step QW, which results in large spin splitting, has advantages in applications to spintronic devices compared with symmetrical and asymmetrical QWs. Due to the special structure design, the spin splitting does not change with the external electric field.

Anisotropic Zeeman splitting and Stark shift of In1-yMnyAs1-xNx oblate quantum dots

The electronic structure, Zeeman splitting, and Stark shift of In1-yMnyAs1-xNx oblate quantum dots are studied using the ten-band k center dot p model including the sp-d exchange interaction between the carriers and the magnetic ion. The Zeeman splitting of the electron ground states is almost isotropic. The Zeeman splitting of the hole ground states is highly anisotropic, with an anisotropy factor of 918 at B=0.1 T. The Zeeman splittings of some of the electron and hole excited states are also highly anisotropic. It is because of the spin-orbit coupling which couples the spin states with the anisotropic space-wave functions due to the anisotropic shape. It is found that when the magnetic quantum number of total orbital angular momentum is nearly zero, the spin states couple with the space-wave functions very little, and the Zeeman splitting is isotropic. Conversely, if the magnetic quantum number of total orbital angular momentum is not zero, the space-wave functions in the degenerate states are different, and the Zeeman splitting is highly anisotropic. The electron and hole Stark shifts of oblate quantum dots are also highly anisotropic. The decrease of band gap with increasing nitrogen composition is much more obvious in the smaller radius case because the lowest conduction level is increased by the quantum confinement effect and is closer to the nitrogen level. (C) 2007 American Institute of Physics.

Effect of a step quantum well structure and an electric-field on the Rashba spin splitting

Spin splitting of conduction subbands in Al_(0.3)Ga_(0.7)As/GaAs/Al_xGa_(1-x)As/Al_(0.3)Ga_(0.7)As step quantum wells induced by interface and electric field related Rashba effects is investigated theoretically by the method of finite difference. The dependence of the spin splitting on the electric field and the well structure, which is controlled by the well width and the step width, is investigated in detail. Without an external electric field, the spin splitting is induced by an in terface related Rashba term due to the built-in structure inversion asymmetry. Applying the external electric field to the step QW, the Rashba effect can be enhanced or weakened, depending on the well structure as well as the direction and the magnitude of the electric field. The spin splitting is mainly controlled by the interface related Rashba term under a negative and a stronger positive electric field, and the contribution of the electric field related Rashba term dominates in a small range of a weaker positive electric field.A method to determine the interface parameter is proposed.The results show that the step QWs might be used as spin switches.

Numerical Investigation On Evolution Of Cylindrical Cellular Detonation

Cylindrical cellular detonation is numerically investigated by solving two-dimensional reactive Euler equations with a finite volume method on a two-dimensional self-adaptive unstructured mesh. The one-step reversible chemical reaction model is applied to simplify the control parameters of chemical reaction. Numerical results demonstrate the evolution of cellular cell splitting of cylindrical cellular detonation explored in experimentas. Split of cellular structures shows different features in the near-field and far-field from the initiation zone. Variation of the local curvature is a key factor in the behavior of cell split of cylindrical cellular detonation in propagation. Numerical results show that split of cellular structures comes from the self-organization of transverse waves corresponding to the development of small disturbances along the detonation front related to detonation instability.

Controllable Kerr nonlinearity with perfect transparency in the existence of spontaneously generated coherence

We investigate the Kerr nonlinearity of a V-type three-level atomic system where the upper two states decay outside to another state and hence spontaneous generated coherence may exist. It is shown that dark state and hence perfect transparency present under certain conditions. Meanwhile, the Kerr nonlinearity can be controlled by manipulation of the decay rates and the splitting of the two excited states. Therefore, enhanced Kerr nonlinearity without absorption can be obtained under proper parameters.

Reflection and transmission of Gaussian beam from a uniaxial crystal slab

We investigate the characteristics of Gaussian beams reflected and transmitted from a uniaxial crystal slab with an arbitrary orientation of its optical axis. The formulas of the total electric and magnetic fields inside and outside the slab are derived by use of Maxwell's equations and by matching the boundary conditions at the interfaces. Numerical simulations are presented and the field values as well as the power densities are computed. Negative refractions are demonstrated when the beam is transmitted through a uniaxial crystal slab. Beam splitting of the reflected beam is observed and is explained by the resonant transmission for plane waves. Dependences of the lateral shift on the incident angle and beam width are discussed. Negative and positive lateral shifts are observed due to the spatial anisotropic properties.

Bulk crystal growth and efficient diode-pumped laser performance of Yb 3+:Sc2SiO5

A bulk crystal of Yb:Sc2SiO5 (Yb:SSO) with favorable thermal properties was successfully obtained by the Czochralski method. The energy level diagrams for Yb:SSO crystal were determined by optical spectroscopic analysis and semi-empirical crystal-field calculations using the simple overlap model. The full width at half maximum of the absorption band centering at 976 nm was calculated to be 24 nm with a peak absorption cross-section of 9.2x10(-21) cm(2). The largest ground-state splitting of Yb3+ ions is up to 1027 cm(-1) in a SSO crystal host. Efficient diode-pumped laser performance of Yb:SSO was primarily demonstrated with a slope efficiency of 45% and output power of 3.55 W.

Mitochondrial molecular clocks and the origin of the major Otocephalan clades (Pisces : Teleostei): A new insight

The Otocephala, a clade including ostariophysan and clupeomorph telcosts, represents about a quarter of total fish species diversity, with about 1000 gencra and more than 7000 species. A series of recent papers have defended that the origin of this clade and of its major groups may be significantly older than the oldest fossils of each of these groups suggest. Some of these recent papers explicitly defend a Pangean origin for some otocephalan groups Such as the Siluriformes or Cypriniformes. To know whether or not the otocephalans as a whole, and particularly the mainly freshwater, cosmopolitan otophysans could have originated before the splitting of the Pangean Supercontinent is of extreme importance, since otophysan fishes are among the most useful animal groups for the determination of historical continental relationships. In the present work we examined divergence times for each major otocephalan group by an analysis of complete mtDNA sequences, in order to investigate if these divergence times support the hypotheses advanced in recent studies. The complete mtDNA sequences of nine representative non-otocephalan fish species and of twenty-one representative otocephalan species was compared. The present study is thus, among the studies dealing with molecular divergence times of telcosts, the one in which a greater number of otocephalan species are included. The divergence times obtained support that the major otocephalan groups had a much older origin than the oldest fossil records available for these groups suggest. The origin of the Otocephala is estimated as having occurred about 282 Mya, with the origin of the Otophysi being estimated at about 251 Mya. (c) 2005 Elsevier B.V. All rights reserved.

Investigation of filling factor in In0.53Ga0.47As/In0.52Al0.48As quantum wells with two occupied subbands

The magnetic field dependence of filling factors has been investigated on InP based In-0.53 Ga0.47As/In-0.52 Al-0.48 As quantum well samples with two occupied subbands by means of magnetotransport measurements at the temperature of 1.5 K in a magnetic field range of 0 to 13 T. Under the condiction that Laundau-level broadening is larger than the spin splitting of each subband, filling factors are even when the splitting energy of two subbands is an integer multiple of the cyclotron energy, i. e. Delta E-21 = khw(c). If the splitting energy of two subbands is half of an odd interger multiple of the cyclotron erergy, i. e. Delta E-21 = (2 k + 1) hw(c) /2, the filling factor is odd.

Magnetic coupling properties of mn-doped ZnO nanowires: First-principles calculations

Based on the density functional theory, we study the magnetic coupling properties of Mn-doped ZnO nanowires. For the nanowires with passivated surfaces, the antiferromagnetic state is found and the Mn atoms have a clustering tendency. When the distance between two Mn atoms is large, the system energetically favors the paramagnetic or spin-glass state. For the nanowires with unpassivated surfaces, the ferromagnetic (FM) coupling states appear between the two nearest Mn atoms, and the zinc vacancies can further stabilize the FM states between them. The electrons with enough concentration possibly mediate the FM coupling due to the negative exchange splitting of conduction band minimum induced by the s-d coupling, which could be useful in nanomaterial design for spintronics. (C) 2008 American Institute of Physics.

Photoluminescence energy and fine structure splitting in single quantum dots by uniaxial stress

We report a photoluminescence (PL) energy red-shift of single quantum dots (QDs) by applying an in-plane compressive uniaxial stress along the [110] direction at a liquid nitrogen temperature. Uniaxial stress has an effect not only on the confinement potential in the growth direction which results in the PL shift, but also on the cylindrical symmetry of QDs which can be reflected by the change of the full width at half maximum of PL peak. This implies that uniaxial stress has an important role in tuning PL energy and fine structure splitting of QDs.