Supersymmetry in74Se,75Se,73As,and74As nuclei

New experimental data, obtained on⁷³As and⁷⁴As, were used to test the predictions of the U(6/12)U (6/12) supersymmetry scheme in its vibrational limit. The level spectra of ₃₄ ⁷⁴ Se₄₀, ₃₄ ⁷⁵ Se₄₁, ₃₃ ⁷³ AS₄₀ and ₃₃ ⁷⁴ As₄₁ supermultiplet nuclei have been calculated using a simple closed energy formula. 44 states in four different nuclei have been reasonably described using only 7 fitted parameters. The existence of supersymmetry was supported also by one-nucleon transfer reaction data, electromagnetic properties, and by a comparison between the supersymmetry and interacting boson-fermion-fermion model wave functions.     

Implantation and diffusion of 73As in GaAs and GaP

Self-diffusion on the As sublattice in intrinsic GaAs and foreign-atom diffusion on the P sublattice in intrinsic GaP were investigated in a direct way by As tracer diffusion measurements using the radioisotope ⁷³As. For this purpose ⁷³As was implanted in both materials at the ISOLDE facility of CERN. Then diffusion annealings were performed followed by serial sectioning and counting of the radioactivity in each section. The resulting profiles were simulated within a computer model which accounts for the observed loss of tracer to the diffusion ambient. The so-obtained diffusion coefficients for As in GaAs and GaP are compared with existing diffusivities in these compounds. This revised version was published online in July 2006 with corrections to the Cover Date.     

Valence band mixing in GaAs-(AlGa)As heterostructures

In optical emission from electrons confined in quantum wells, the component with polarization normal to the planes was observed to be unexpectedly strong. This suggests a breakdown of the point group symmetry of the highest valence state beyond the reduction from cubic to laminar symmetry. Effective mass theories that include excitonic interactions and conventional symmetry-breaking mechanisms do not account for this phenomenon.     

Microscopic analysis of the valence band and impurity band theories of (Ga,Mn)As

We analyze microscopically the valence and impurity band models of ferromagnetic (Ga,Mn)As. We find that the tight-binding Anderson approach with conventional parametrization and the full potential local-density approximation+U calculations give a very similar band structure whose microscopic spectral character is consistent with the physical premise of the k·p kinetic-exchange model. On the other hand, the various models with a band structure comprising an impurity band detached from the valence band assume mutually incompatible microscopic spectral character. By adapting the tight-binding Anderson calculations individually to each of the impurity band pictures in the single Mn impurity limit and then by exploring the entire doping range, we find that a detached impurity band does not persist in any of these models in ferromagnetic (Ga,Mn)As.     

Decoupled bands in odd-mass mercury isotopes

The schemes of the low-lying high-spin states in mercury isotopes with A = 195, 197, and 199 have been studied by γ-ray spectroscopy following (α, xn) reactions on separated platinum targets. Two bands have been excited in each Hg nucleus, one with positive parity based on the isomeric i$\text{13}\text{2}$. state and one, probably with negative parity, starting at spin $\text{case21}\text{2}$. The positive-parity states are interpreted with the rotation-aligned coupling scheme as decoupled bands; this implies oblate deformation in these three Hg isotopes. The negative-parity states are discussed as a decoupled i$\text{13}\text{2}$ neutron state coupled to the 5^?, 7^?, 9^?,…states, recently discovered in doubly even mercury isotopes.     

The quadrupole moment of the 66 keV, 5/2− state of73As

⁷³Se was produced by proton irradiation of polycrystalline arsenic. The quadrupole interaction of the 66 keV, 5/2^? state in the daughter isotope⁷³As with the electric field gradient in the noncubic arsenic lattice was observed at room temperature by means of theγ-γ perturbed angular correlation technique. The measured angular correlation pattern is characterized by a quadrupole coupling constantv _Q =51.6 (1.3) MHz. By use of the known electric field gradient on regular lattice sites, a value of ¦Q¦=0.356(12)b is derived for the quadrupole moment of the 66 keV, 5/2^? state of⁷³As.     

Decoupled anisotropic spheres in self-interacting Brans-Dicke gravity

The focus of this paper is to obtain anisotropic spherically symmetric solutions by means of gravitational decoupling in the background of self-interacting Brans-Dicke theory. We introduce minimal geometric deformation in the radial metric component to decouple the field equations into two arrays. The first set, governed by the seed source, is determined through metric functions of isotropic solution (Heintzmann/Tolman VII spacetimes) while the second set is solved by imposing two constraints on the anisotropic source. The unknown constants are evaluated via matching conditions at the stellar boundary. We investigate the effects of massive scalar field as well as decoupling parameter on the physical structure of anisotropic models and check them for viability through energy conditions. It is concluded that the anisotropic solutions obtained through constraint I are well-behaved for selected values of the decoupling parameter. For the second constraint, the extended Heintzmann solution is viable but anisotropic Tolman solution does not comply with dominant energy condition for higher values of the decoupling parameter.     

Optical studies on the band structure of Ga0.08In0.92As0.18P0.82

Reflection and transmission spectra of liquid phase-grown Ga_0.08In_0.92As_0.18P_0.82 layers deposited on (100) - oriented InP single crystals were experimentally investigated. From a comparison of the known bandstructure of InP, assignments of the observed optical transitions in the quaternary alloy have been made.     

Energy band modulation of GaAs/Al0.26Ga0.74As quantum well in 3D self-assembled nanomembranes

In this study, we investigate the modulation of energy band in 3D self-assembled nanomembranes containing GaAs/Al_0.26Ga_0.74As quantum wells (QWs). Photoluminescence (PL) characterizations demonstrate that the self-assembled structures have different optical transition properties and the modulation of the energy band is thus realized. Detailed spectral analyses disclose that the small strain change in structures with different curvatures cannot cause remarkable change in energy bands in Al_0.26Ga_0.74As layer. On the other hand, the optical transitions of GaAs QW layer is influenced by the strain evolution in term of light emission intensity. We also find the first order Stark effect in rolled-up nanomembrane with diameter of 150 μm, which is closely connected with the coupling effect between the deformation potential and the piezoelectric potential. Our work may pave a way for the fabrication of high performance rolled-QW infrared photo-detectors.     

Study of 71, 73, 75, 77As with Ge(3He,d) reactions

Studies of ^{71, 73, 75, 77}As isotopes using Ge(³He, d) reactions have enabled the identification of many previously unreported levels together with new spin-parity assignments. A comparison of the results with the predictions of the model of Scholz and Malik shows good agreement for both positive- and negative-parity states.     

Lifetimes in73Se

Lifetimes of 8 levels in⁷³Se have been measured by the recoil distance Doppler shift technique via the reaction⁶⁰Ni(¹⁶O, 2pn)⁷³Se. Energies of negative and positive parity states as well asE 2 transition strengths are compared with theoretical values obtained from a symmetric rotor plus particle model and a triaxial rotor model.     

On the decay of73Ga to levels in73Ge

Theγ-radiation following the β^? decay of⁷³Ga has been studied. Singlesγ andγγ coincidence spectra were recorded with Ge(Li)-detectors. 17γ-rays were assigned to transitions in⁷³Ge, where 11 excited levels are proposed. From logft values based onγ-transition intensities, spin and parity assignments for the levels were deduced. The half-life of⁷³Ga was measured to (4.86±0.03) h. From allowedβ-transitions the ground state of⁷³Ga was assigned 3/2^?.     

Decoupled Hartree—Fock methods. III

Acta physica Academiae Scientiarum Hungaricae -     

Two-electron band to band transitions in silicon

Radiative two-electron band to band transitions are investigated experimentally in silicon. The question of phonon-participation is investigated. It turns out that at low temperature the phononless transitions dominate, whereas above room-temperature the phonon-assisted transitions become more important. A theoretical discussion leads to the conclusion that at least one participating phonon is an acoustical one.     

Decoupled phase transitions and grain-boundary melting in supported phospholipid bilayers

Two separate liquid-solid phase transitions are detected in the two monolayers of a mica-supported phospholipid bilayer by atomic force microscopy. The phase transitions of the two monolayers are decoupled by the stronger interaction between the lipid headgroups of the proximal monolayer and the mica support. The transition temperature of the proximal monolayer is increased and this transition occurs over a narrower temperature range. Both transitions occur via grain-boundary melting and the variation of the width of the interfacial zone with temperature is consistent with mean-field theory.