Three body interaction in breathing shell model

It is shown that the dominant contribution of the breathing degree of freedom of the electron charge cloud is an effective three body interaction and an attractive two body interaction in addition to the usual overlap interaction. The explicit forms for these interactions are obtained and it is found that the form of the three body interaction is identical to that given in the deformable shell model (DSM).     

Optical phonons in quantum-wire structures

The optical vibrational modes in GaAs/AlAs structures grown on a (311)A-oriented GaAs surface are investigated. It is found that the line corresponding to the fundamental TO vibrational mode localized in a GaAs quantum wire is split into two lines with different directions of the polarization vector. The dispersion of the TO phonons of GaAs in the (311) direction is determined from the IR spectra of periodic structures. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 107–110 (25 January 1998)     

The shell model and collective structures in54,55,56Fe

Extensive shell-model calculations have been performed on^54,55,56Fe. The results obtained in a model space with two and with up to threef _7/2 holes in the,⁵⁶Ni core are compared with experiment. The Surface Delta Interaction (SDI) and the Kuo Brown interaction (KB) have been used to calculate energy levels, spectroscopic factors and electromagnetic properties resulting especially for⁵⁶Fe in a remarkably good agreement with experiment. Admixtures of three-hole components in the wave functions are significant and increase with mass number. Properties of high-spin states withJ≦15 are discussed. Pronounced collective features derived microscopically are expected in⁵⁶Fe. Finally some suggestions for interesting experiments are given.     

Anisotropic scattering of holes by acoustic and optical phonons in germanium

The anisotropic scattering of holes by acoustic and optical phonons in germanium is investigated with allowance for the complex structure of the energy spectrum and the specifics of the scattering mechanisms. The temperature dependence of the hole mobility is analyzed in the temperature interval 10°K T 300°K. The results are in good agreement with the experimental data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 3–7, May, 1982.     

Interface phonons in asymmetric quantum well structures

In semiconductor microstructures with many layers, the phonon modes change from their bulk form and split into ‘confined LO phonons’ (LC) and ‘interface phonons’ (IF), the number and variety of which depends on both the number of layers and the number of different materials in the structure. This affects the electron–phonon scattering rates. Because of the current interest in inter-subband THz emitters, we use these LC and IF modes to evaluate the inter-subband electron–phonon scattering rate in THz emitter prototypes that are based on four-subband stepped quantum wells. These scattering rates in turn affect the population inversion predicted for these devices, so we compare the predicted population inversions for the most promising prototypes against those obtained using bulk phonon scattering rates.     

Stresses in shell structures

In this paper the stresses obtained for various (thin) shell structures by using two types of doubly curved finite elements are compared with published information. One of the elements—a ring shell element—is designed to analyze axisymmetric structures such as cylinders and hyperboloids. The accuracy and convergence of this element is shown to be excellent. The other element—a quadrilateral shell element—is designed to calculate stresses, mode shapes and frequencies of axisymmetric structures as well as sections of shell structures. The quadrilateral element is more versatile than the ring element. However, it is found that the convergence of the ring element is superior to that of the quadrilateral element. The resonant stresses of a hyperboloidal shell structure have been presented, and, as far as the author is aware, a similar investigation has not previously been reported in the literature. Whilst the primary purpose of the paper is to examine the usefulness of the two doubly curved elements in the analysis of shell structures, the examples considered in the text are described in detail to facilitate comparative structures by future investigators.     

Imaging of spatial structures in crystals with ballistic phonons

Ballistic phonon propagation in single crystals has been used for imaging defect structures in bulk material. We have realized this principle by means of low-temperature scanning electron microscopy. As model cases we have imaged laser drilled holes in single-crystalline sapphire and -quartz samples. Comparing the acoustic images with those obtained by optical transmission microscopy, we found that fine structure seen optically was well reproduced acoustically. In addition strain fields due to plastic deformations could clearly be imaged acoustically. The spatial resolution of our imaging technique is estimated to be a few micrometer. By using two or more phonon detectors, three-dimensional imaging of spatial inhomogeneities becomes possible.     

Exciton energy relaxation on acoustic phonons in double-quantum-well structures

The paper analyzes the rate of energy relaxation involving acoustic phonon emission between exciton states in a double quantum well. A theoretical study is made of the part played by two mechanisms, one of which is a one-step transition with emission of an acoustic phonon and the other is a two-step transition, which includes elastic exciton scattering from interface nonuniformities followed by energy relaxation within an exciton subband. The rate of the two-step transition in real double quantum wells is shown to be higher than that of the one-step transition. As follows from calculations, the fast energy relaxation between exciton states is determined by the elastic scattering of phonons from the interface.     

Anisotropic thermopower in tilted metallic multilayer structures

Thermoelectric fields transverse to an applied temperature gradient are observed in tilted metallic multilayer structures. Constantan–chromel multilayers are prepared by sintering stacks of alternating thin foils of these materials. Effective in-plane and out-of-plane Seebeck coefficients and heat conductivities of the foil stacks are calculated from data for the isotropic metals. Tilted multilayer structures obtained by cutting stacks obliquely may be used as devices for detecting laser radiation. The thermoelectric response of several multilayer structures and anisotropic crystalline systems is compared PACS 07.07.Df; 07.57.Kp     

Anisotropic voter model

A majority vote model subject to anisotropic voting rules is studied in two dimensions using a first-order mean-field approximation and Monte Carlo simulations. The critical behavior is consistent with the 2D Ising universality class.     

Thermal transport associated with ballistic phonons in asymmetric quantum structures

Using the scattering matrix method, we investigate the thermal conductance associated with ballistic phonons at low temperatures in asymmetric quantum structures. The results show that when the structure is an ideal quantum wire, the universal value π ² κ _B²(3h) can be observed at very low temperatures. However, for asymmetric quantum structure, the thermal conductance is less than the universal value π ² κ _B²(3h), even at T → 0. The results also show that the thermal conductance is strongly dependent on the transport direction. The rectification effect can be observed in the asymmetric structure and can be adjusted by changing the structural parameters. A brief analysis of these results is given.      

Dissolution of shell structures in exotic nuclei

Nuclear many-body theory is used to study nuclear matter and finite nuclei at extreme isospin. In-medium interactions in asymmetric nuclear matter are obtained from (Dirac-) Brueckner theory. Neutron skin formation in Ni and Sn isotopes is investigated in relativistic DDRH theory with density dependent meson-nucleon vertices. Applications to light nuclei are discussed with special emphasis on pairing and core polarization in weakly bound nuclei. The calculations show that shell structures are dissolving when the driplines are approached.     

Anisotropic hubble expansion of large scale structures

With the aim of understanding the cosmic velocity fields at large scale, we investigate the dynamics of a pressureless distribution of gravitational sources moving under an anisotropic generalization of Hubble expansion and according to Euler-Poisson equations system. As a result, it turns out that such a behavior requires the distribution to be homogenous, similarly to Hubble law. Among several solutions, we show a planar kinematics which admits a constant (eternal) and rotational distortion, where the velocity field is not potential. Within this class, the one with no rotational distortion identifies to a bulk flow. To apply this model within cosmic structures as the Local Super Cluster, the solutions are interpreted as approximations providing us with an hint on the behavior of the cosmic flow just after decoupling era up to present date. Such a result suggests that the observed bulk flow may not be due exclusively to tidal forces but has a primordial origin. UPRES EA 2596. Unité Mixte de Recherche (UMR 6207) du CNRS, et des universités Aix-Marseille I, Aix-Marseille II et du Sud Toulon-Var. Laboratoire affiliéà la FRUMAM (FR 2291).     

Anisotropic x-ray scattering from simulated amorphous structures

Two 800-atom cluster models of amorphous copper were constructed utilizing the method of continuous static relaxation of nonrigid spheres developed by the authors. The Morse and Ballog potentials were used to construct and relax the structures. The angular dependence of the x-ray scattering was simulated for both clusters, and a rather appreciable anisotropy was found for them. In order to elucidate the causes of the observed anisotropy, a distribution of atoms in thin sections perpendicular to the direction of the main peak was investigated. Quasiperiodic fluctuations in the occupation numbers of the sections with a period roughly corresponding to the radius of the first coordination sphere were found. A special numerical—graphical analysis showed that the atoms contributing to the main peak form pseudoplanes corresponding to fluctuations in the occupation numbers of the sections. In spite of appreciable differences in the character of interatomic interactions, the density, and the microstructure of the modeled clusters, the pseudocrystalline motifs in both clusters were very similar. A comparison was performed of the results obtained from the scattering pattern for an 800-atom unrelaxed stochastic cluster especially generated for the investigation of the influence of relaxation on the anisotropy. It is shown that the relaxation somewhat increases the anisotropy and order the displacement of the atoms within the sections although on the whole the scattering pattern in all cases is similar. The results obtained correlate well with published data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 7–12, August, 1993.     

Anisotropic plasmon dispersion and damping in multilayer 8-Pmmn borophene structures

We investigate the collective plasma oscillations theoretically in multilayer 8-Pmmn borophene structures, where the tilted Dirac electrons in spatially separated layers are coupled via the Coulomb interaction. We calculate the energy dispersions and Landau dampings of the multilayer plasmon excitations as a function of the total number of layers, the interlayer separation, and the different orientations. Like multilayer graphene, the plasmon spectrum in multilayer borophene consists of one in-phase optical mode and N - 1 out-of-phase acoustical modes. We show that the plasmon modes possess kinks at the boundary of the interband single-particle continuum and the apparent anisotropic behavior. All the plasmon modes approach the same dispersion at a sufficiently large interlayer spacing in the short-wavelength limit. Especially along specific orientations, the optical mode could touch an energy maximum in the nondamping region, which shows non-monotonous behavior. Our work provides an understanding of the multilayer borophene plasmon and may pave the way for multilayer borophene-based plasmonic devices.     

Ionic shell and subshell structures in aluminum and gold nanocontacts

Conductance histograms of aluminum and gold nanocontact rupture are studied experimentally and simulated using embedded atom potentials to assess the interplay between electronic and structural properties at room temperature. Our results reveal a crossover from quantized conductance structures to crystalline faceting or geometric shell/subshell structures at 300 K. The absence of electronic shell structure in gold and aluminum is in stark contrast with the behavior of alkaline metal nanowires which emulate their cluster counterparts. Semiclassical arguments suggest why rapid dominance of ionic structures takes place, and possible nanowire architectures are proposed in consistency with both the experimental and simulated nanocontact data.