Magnetic ordering and irreversible magnetization between ZFC and FC states in RCo5Ga7 compounds

The magnetic properties of RCo5Ga7 (R = Y, Tb, Dy, Ho and Er) compounds which crystallize in the ScFe6Ga6-type structure have been studied. The compounds with R, Y, Tb, Dy, Ho and Er display behaviour similar to semiconductors. The Co transition metal sublattice is ferrimagnetic with a very low spontaneous magnetization. The ferrimagnetic ordering observed for R = Y, Tb, Dy, Ho and Er is due to the transition metal sublattice with transition temperatures at about 295 K. At low temperatures, the magnetic ordering for R Tb, Dy, Ho and Er is due to the rare-earth sublattice, which is ferromagnetic with a Curie temperature below 5 K. By fitting the linear part of the inverse magnetization, the effective magnetic moment of the R ion is found to be close to its expected theoretical value, with paramagnetic Curie temperatures below 5 K. Due to the paramagnetic nature of the R sublattice above 60 K, the ferrimagnetic ordering temperature of the Co sublattice does not vary with the type of rare-earth ion. The irreversibility of the magnetization of YCo5Ga7, as measured in zero-field cooled (ZFC) and field cooled (FC) states, is attributed to movement of domain walls. Application of a large enough applied field completes the movement of the domain wall from the low-temperature to the high-temperature one at 5 K. With a very low magnetic field 100 Oe, the difference between the ZFC and the FC shrinks. (C) 2004 Elsevier B.V. All rights reserved.

Method for generating maximally entangled states of multiple three-level atoms in cavity QED

We propose a scheme to generate maximally entangled states (MESs) of multiple three-level atoms in microwave cavity QED based on the resonant atom-cavity interaction. In the scheme, multiple three-level atoms initially in their ground states are sequently sent through two suitably prepared cavities. After a process of appropriate atom-cavity interaction, a subsequent measurement on the second cavity field projects the atoms onto the MESs. The practical feasibility of this method is also discussed.

Observation of antiphase states in a passively Q-switched multimode microchip Yb : YAG laser with a GaAs saturable absorber

Antiphase dynamics has been observed experimentally for the laser modes operation in a laser-diode-pumped Q-switched microchip Yb:YAG laser with GaAs as a saturable absorber in the presence of spatial hole-burning. The Q-switched pulses sequences of two modes at different pump power have been obtained. The experimental results have shown that the pulses sequences displayed classic antiphase dynamics. (C) 2003 Elsevier B.V. All rights reserved.

Observation of intershell and hybridized energy states in InAs/GaAs quantum dots

We have investigated the evolution of exciton state filling as a function of excitation power density in InAs/GaAs quantum dots (QDs). In addition to the emission bands of exciton recombination corresponding to the atom-like S, P, and D, etc. shells of quantum dots, it was observed that some extra states, P-' (between the S and P shells) and D-' (between the P and D shells), appear in the spectra with increasing number of excitons occupying the QDs. The emergence of these intershell excitonic levels is an experimental demonstration of strong exciton-exciton exchange interaction and coupling as well as state mixing and hybridization of a multiexciton system in quantum dots.

Theoretical analysis of gate voltage-controlled subband states in an AlxGa1-xN/GaN heterostructure

The subband structure and inter-subband transition as a function of gate voltage are determined by solving the Schrodinger and Poisson equations self-consistently in an AlxGa1-xN/GaN heterostructure. Different aluminum mole fraction and thickness of AlxGa1-xN barrier are considered. Calculation results show that energy difference between the first and second subband covers a wide range (from several tens to hundreds milli-electron volt) by applying different gate voltage, which corresponds to the midinfrared and long-wave infrared wavelength scope. Furthermore, such a modulation on the subband transition energy is much more pronounced for the structure with thin barrier. When the applied positive gate voltage is increased, the triangle well formed at the interface turns to be deeper and narrower, which enhances the confinement for electrons. As a result, the overlap between electron wave function at two subbands increases, and thus the optical intersubband transition also enhances its intensity. This tendency is in good agreement with the available data in the literature. (c) 2005 Elsevier B.V. All rights reserved.

Optical properties of alloy states in GaNxAs1-x (x < 0.01)

A set of GaNxAs1-x samples with a small content of nitrogen (N) (< 1%) were investigated by continuous-wave photoluminescence (PL), pulse-wave excitation PL, and photo reflectance technology. Temperature-and excitation-dependence of PL disclosed the intrinsic band gap properties of alloy states in GaNxAs1-x, which was extremely different from the N-related impurity states. At the same time, PR spectra were also studied in this work.

A criterion for local interconvertibility between all-tripartite Gaussian states

We arrive at a necessary and sufficient criterion that can be readily used for interconvertibility between general, all-tripartite Gaussian states under local quantum operation. The derivation involves a systematic reduction that converts the original complex conditions in high-dimensional, 6n x 6n matrix space eventually into 2 x 2 matrix problems.

Electronic states of a hydrogenic donor impurity in semiconductor nano-structures

We propose a method for uniformly calculating the electronic states of a hydrogenic donor impurity in low-dimensional semiconductor nano-structures in the framework of effective-mass envelope-function theory, and we study the electronic structures of this systems. Compared to previous methods, our method has the following merits: (a) It can be widely applied in the calculation of the electronic states of hydrogenic donor impurities in nano-structures of various shapes; (b) It can easily be extended to study the effects of external fields and other complex cases; (c) The excited states are more easily calculated than with the variational method; (d) It is convenient to calculate the change of the electronic states with the position of a hydrogenic donor impurity in nano-structures; (e) The binding energy can be calculated explicitly. (c) 2007 Elsevier B.V. All rights reserved.

Spin states and persistent currents in mesoscopic rings: Spin-orbit interactions

We investigate theoretically electron spin states in one-dimensional and two-dimensional (2D) hard-wall mesoscopic rings in the presence of both the Rashba spin-orbit interaction (RSOI) and the Dresselhaus spin-orbit interaction (DSOI) in a perpendicular magnetic field. The Hamiltonian of the RSOI alone is mathematically equivalent to that of the DSOI alone using an SU(2) spin rotation transformation. Our theoretical results show that the interplay between the RSOI and DSOI results in an effective periodic potential, which consequently leads to gaps in the energy spectrum. This periodic potential also weakens and smoothens the oscillations of the persistent charge current and spin current and results in the localization of electrons. For a 2D ring with a finite width, higher radial modes destroy the periodic oscillations of persistent currents.

Passively mode-locked Nd : YVO4 laser using semiconductor saturable absorption mirrors of interface states relaxation region

Semiconductor saturable absorber mirrors (SESAMs) with GaAs/air interface relaxation region have less nonsaturable loss than those with low temperature grown In0.25Ga0.75As relaxation region. A thin layer Of SiO2 and a high reflectivity film Of Si/(SiO2/Si)(4) were coated on the SESAMs, respectively in order to improve the SESAM's threshold for damage. The passively continuous wave mode-locked lasers with two such SESAMs were demonstrated, and the SESAM with high reflectivity film of Si/(SiO2/Si)(4) is proved to be helpful for high output power. (c) 2006 Elsevier GmbH. All rights reserved.

Light-propagation characteristics of photonic crystal waveguide based on SOI materials at different polarized states

Straight single-line defect optical waveguides in photonic crystal slabs are designed by the plane wave expansion method and fabricated into silicon-on-insulator (SOI) wafer by 248-nm deep UV lithography. We present an efficient way to measure the light transmission spectrum of the photonic crystal waveguide (PhC WG) at given polarization states. By employing the Mueller/Stokes method, we measure and analyse the light propagation properties of the PhC WG at different polarized states. It is shown that experimental results are in agreement with the simulation results of the three-dimensional finite-difference-time-domain method.

Application of plane wave method to the calculation of electronic states of nano-structures

The electronic states of nano-structures are studied in the framework of effective-mass envelope-function theory using the plane wave basis. The barrier width and the number of plane waves are proposed to be 2.5 times the effective Bohr radius and 15(n), respectively, for n-dimensional nano-structures (n = 1,2,3). Our proposals can be widely applied in the design of various nano-structure devices.

Exciton states of vertically stacked self-assembled InAs quantum disks in an axial magnetic field

We have studied the exciton states of vertically stacked self-assembled quantum disks within the effective mass approximation. The ground energies of a heavy-hole and a light-hole excitons as functions of the vertical disk separation are presented and discussed. The transition energy of a heavy-hole ground-state exciton is calculated and compared with the experimental data. The binding energies are discussed in terms of the probability of ground wave function. The ground energies of a heavy-hole and a light-hole excitons as functions of the applied axial magnetic field are calculated and the effect of disk size (radius of disks) on exciton energies is discussed. (c) 2006 Elsevier B.V. All rights reserved.

Photoluminescence from the nitrogen-perturbed above-bandgap states in dilute GaAs1-xNx alloys: A microphotoluminescence study

Using microphotoluminescence (mu-PL), in dilute N GaAs1-xNx alloys, we observe a PL band far above the bandgap E-0 with its peak energy following the so-called E+ transition, but with contribution from perturbed GaAs host states in a broad spectral range (> 100 meV). This finding is in sharp contrast to the general understanding that E+ is associated with a well-defined conduction band level (either L-1c or N-x). Beyond this insight regarding the strong perturbation of the GaAs band structure caused by N incorporation, we demonstrate that a small amount of isoelectronic doping in conjunction with mu-PL allows direct observation of above-bandgap transitions that are not usually accessible by PL.

Lifetime study of N impurity states in GaAs1-xNx (x=0.1%) under hydrostatic pressure

The lifetimes of a series of N-related photoluminescence lines (A(2)-A(6)) in GaAs1-xNx (x=0.1%) were studied under hydrostatic pressures at similar to 30 K. The lifetimes of A(5) and A(6) were found to increase rapidly with increasing pressure: from 2.1 ns at 0 GPa to more than 20 ns at 0.92 GPa for A(5) and from 3.2 ns at 0.63 GPa to 10.8 ns at 0.92 GPa for A(6). The lifetime is found to be closely correlated with the binding energy of the N impurity states, which is shown either in the pressure dependence for a given emission line or in the lifetime variation from A(2) to A(6). (c) 2006 American Institute of Physics.