ARPES measurements on Si(1 1 1) hole subband induced by Pb and Ga adsorption

The subband dispersions in the Si(1 1 1) p-type inversion layers induced by Pb and Ga adsorbed surface structures were measured by angle-resolved photoemission spectroscopy (ARPES). The surface structures used here were and Si(1 1 1)6.3 × 6.3-Ga. is a new surface phase found in this study. Because it is significant in our study to investigate potential effects of surface superstructures on the hole subband dispersion, we investigated the subband energy levels quantitatively comparing them with those calculated using the triangular approximation. It was found that the energy separation of the adjacent subband quantum levels in the inversion layers induced by gallium adsorption does not follow the triangular approximation. The possible band bending shape was proposed to explain the quantum level spacing of the subbands in Ga-induced inversion layers.     

The electronicg-factor anisotropy determined from measurements near the magic field of anomalous muonium in silicon and germanium

The field dependences of the anomalous muoniumSR frequencies have been measured in Si and Ge around the magic field. The results show a clear electronicg-factor anisotropy exists for Ge withg _¦-g₁=0.033, while that of Si is much smaller and essentially zero within the experimental accuracy.Work supported by National Science Foundation Grant DMR-79-09223.     

Optical anisotropy in nonpolar (101̄0)-oriented m-plane GaN/AlGaN quantum wells and comparison with experiment

Optical anisotropy in nonpolar ()-oriented m-plane GaN/InGaN quantum wells was investigated using the multi-band effective-mass theory. The optical matrix element near the Γ point (k_||=0) is shown to increase with increasing polarization angle ϕ’. The anisotropy calculated at the Γ point (k_||=0) is nearly 1 and it rapidly decreases with increasing in-plane wave vector. The reduction of the anisotropy at a large k_|| is attributed to the fact that the state of the first subband is equally mixed of |X〉 and |Y〉 at a large k_||. The photoluminescence intensity increases with ϕ’, becomes a maximum at ϕ’=π/2, and decreases again when ϕ’ further increases. The theoretical result is found to be in good agreement with the experimental results. PACS 85.60.Bt; 85.30.De; 85.30.Vw; 78.20.Bh     

Specific features of the properties of half-metallic ferromagnetic Heusler alloys Fe<Subscript>2</Subscript>MnAl,Fe<Subscript>2</Subscript>MnSi,and Co<Subscript>2</Subscript>MnAl

The structural, magnetic, and electrical properties of half-metallic Heusler alloys Fe₂MnAl, Fe₂MnSi, and Co₂MnAl have been investigated in the temperature range of 4–900 K. According to the X-ray diffraction analysis, these alloys have the B2 and L2₁ structures with different degrees of atomic order. The magnetic state of the alloys is considered as a two-sublattice ferrimagnet. The electrical resistivity and thermoelectric power have been discussed in the framework of the two-current conduction model taking into account the existence of an energy gap in the electronic spectrum of the alloys near the Fermi level for the subband with spin-down (minority) electrons.     

The magnetic anisotropy of manganate ferrites

The anisotropy constants K₁ for systems Mn_xFe_3–xO₄, with 1x 1·8, are calculated on the basis of the one-ion model and it is shown that the anomalous temperature dependence of the constant K₁ can be explained by the presence of Mn³⁺ ions in octahedral positions. The influence of the spin order on the magnetic anisotropy and the uniaxial anisotropy in systems Mn_xFe_3–xO₄ are discussed.     

Spin-polarized transport induced by photoirradiation in zigzag silicene nanosystem

We study the spin-polarized transport induced by photoirradiation in zigzag silicene nanosystem, based on tight-binding approach, Green's function method and Landauer–Büttiker formula. By applying strong circular polarized light, silicene nanosystem can be transformed into a quantum Hall insulator, where the spin-down subband is gapped while the spin-up subband persists gapless edge state. Therefore, the dc conductance is dominated by the spin-up electrons, and the spin polarization can reach almost 100% around the Fermi energy. The spatial-resolved local density of states confirm that the spin-up electrons transport at two edges of the nanosystem in opposite current directions. Furthermore, because of the topological origin of the edge state, the spin-polarized transport is very robust against the size change of the nanosystem.     

Optical anisotropy at the W(1 1 0) surface

We report ab initio calculations of the anisotropic dielectric function of tungsten (1 1 0) surface using the linear muffin-tin-orbital method. The calculated anisotropy in the optical spectrum, for polarization of light parallel to the surface, exhibits three dominant broad structures at 3.00, 4.01 and 5.34 eV successively positive, negative and then positive. The first peak is clearly assigned to p → d interband transitions in surface atomic sites whereas the two others have their origin in interband transitions in bulk like atoms. Our results, including the interlayer relaxation effect on the surface optical response, are compared to recent reflectance anisotropy measurements.     

Method of a singular point and determination of fields of anisotropy of polycrystalline hexagonal magnets

A numerical computation is performed on the magnetization curves and their derivatives for magnets of hexagonal syngony for isotropic polycrystalline specimens as well as materials with sheet texture in the basis plane. It is shown that investigation of the second derivatives ²M/H² for a degree of texture f_T > 0.4 permits obtaining information about the magnitude of the anisotropy field independently of its type. The singularities of M(H) and ²M/H² are examined for magnetization processes of the first kind. In this case the singular point method permits measuring the magnitude of the critical fields, the critical magnetizations, and the anisotropy field on a textured specimen with f_T>0.7, which yields information about the magnitudes of the high order anisotropy constants in the long run.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 39–42, January, 1989.     

Momentum distributions in fragmentation reactions with relativistic heavy ions

The momentum distribution (or angular distribution) in inelastic heavy ion reactions is calculated by using a two-step model (abrasion and ablation). First, all nucleons in the volume element where projectile and target overlap spatially during the collision are sheared away. The remaining prefragment (the projectile minus the sheared off nucleons) has a recoil momentum proportional to the Fermi momentum. The prefragment is left in an excited state and emits nucleons, the recoil momentum given to the final fragment is proportional to the nuclear temperature. This two-step model reproduces the overall trend and the isotopic dependence for the widths of the experimental momentum distributions. Contrary to previous theoretical studies we find that surface and friction phenomena lead to an anisotropy: The momentum distributions in transverse direction are always broader than in the longitudinal direction by about 5 to 10%.     

Violation of the Mott-Ioffe-Regel limit: high-temperature resistivity of itinerant magnets Srn+1RunO3n+1 (n=2,3,∞) and CaRuO3

Sr_n+1Ru_nO_3n+1 represents a class of layered materials whose physical properties are a strong function of the number of Ru-O layers per unit cell, n. These materials along with the paramagnetic CaRuO₃ shares two major characteristics, namely, robust Fermi liquid behavior at low temperatures and anomalous transport behavior featured by linear temperature dependence of resistivity at high temperature. There is no crossover separating such two fundamentally different states. In this paper, we report results of our study that systematically addresses anisotropy and temperature dependence of resistivity as a function of n for the entire Sr_n+1Ru_nO_3n+1 series and CaRuO₃ and for a wide temperature range of It is found that the anomalous transport behavior correlates with magnetic susceptibility and that the scattering mechanism(s) driving the anomalous transport behavior becomes stronger with reducing dimensionality.     

The magnetic behavior of Co atoms on the surface and in the interior of the noble metals Au,Ag and Cu

The magnetism of Co atoms in the interior and on the surface of the noble metals has been studied by means of the anomalous Hall effect. On the surface of all three noble metals Co possesses a magnetic moment even at lowest studied coverages of 0.02 atomic layers. Ferromagnetic ordering appears at Co thicknesses of about one atomic layer. Co as a bulk impurity is non-magnetic in Cu whereas it is magnetic in Ag.     

A Method for Separating the Point-Source Foreground from the Cosmic Microwave Background Maps

We propose a new technique for high-accuracy reconstruction of the cosmic microwave background (CMB) anisotropy from observations contaminated by unresolved extragalactic point sources and pixel noise. The fundamental difference of this technique from the methods suggested before consists in reconstructing the CMB temperature fluctuations in regions contaminated by point sources with allowance for a priori information on the boundedness and spherical symmetry of the spatial power spectrum of the CMB anisotropy, which obeys the Gaussian statistics. The problems of deconvolving the initial maps, localizing point sources, and interpolating the CMB values in the holes are solved by using effective modifications of the well-known maximum entropy method. The results of simulations demonstrate the possibility of achieving the highest accuracy.     

Nature of the anomaly in the temperature dependence of the deformation resistance of aged steel Ni36Cr12TiAl

The appearance of an anomaly in the temperature dependence of the deformation resistance of aged steel Ni36Cr12TiAl may be due to: 1) an anomalous temperature change in the yield point of the '-phase; and 2) strain aging. The first cause plays a decisive part in those cases in which dislocations cut through the '-phase particles during deformation. However, in those cases where the '-particles are impenetrable, the anomaly is due to strain aging.     

Perpendicular magnetic anisotropy of ultrathin FeCo alloy films on Pd(0 0 1) surface: First principles study

Using the full potential linearized augmented plane wave (FLAPW) method, thickness dependent magnetic anisotropy of ultrathin FeCo alloy films in the range of 1 monolayer (ML) to 5 ML coverage on Pd(0 0 1) surface has been explored. We have found that the FeCo alloy films have close to half metallic state and well-known surface enhancement in thin film magnetism is observed in Fe atom, whereas the Co has rather stable magnetic moment. However, the largest magnetic moment in Fe and Co is found at 1 ML thickness. Interestingly, it has been observed that the interface magnetic moments of Fe and Co are almost the same as those of surface elements. The similar trend exists in orbital magnetic moment. This indicates that the strong hybridization between interface FeCo alloy and Pd gives rise to the large magnetic moment. Theoretically calculated magnetic anisotropy shows that the 1 ML FeCo alloy has in-plane magnetization, but the spin reorientation transition (SRT) from in-plane to perpendicular magnetization is observed above 2 ML thickness with huge magnetic anisotropy energy. The maximum magnetic anisotropy energy for perpendicular magnetization is as large as 0.3 meV/atom at 3 ML film thickness with saturation magnetization of . Besides, the calculated X-ray magnetic circular dichroism (XMCD) has been presented.     

Generating functionals and the Ising model

The Ising model is studied by the generating functional approach in order to provide a better understanding of that method. It is shown how to derive a general solution of a functional equation in terms of infinite-dimensional integrals. This solution is not unique; the different possibilities are characterized by different paths of integration. Further, the saddle point approximation is used for the integrals in order to obtain second-order correlation functions. It is shown that besides the normal solution, one obtains several anomalous ones, which correspond directly to the nonphysical solutions of the transfer matrix method for treating the partition function. It is also shown that only the correct solution can give a realistic behavior of the correlation function at large distances. The relevance of the saddle point methods for describing phase transitions is also discussed.     

Electronic structure of two coupled Si δ-doped GaAs as dependent on the donor thickness

For the uniform distribution we have theoretically investigated the influence of donor thickness on two coupled Si -doped GaAs structure, at T=0 K. Electronic structure have been calculated by solving the Schrödinger and Poisson equations self-consistently. We thus find the confining potential, the electronic density, the subband energies and their eigen envelope functions, the subband occupations and Fermi energy. From the self-consistent calculation, we have seen that the effective potential profile and the electronic density of two coupled Si -doped GaAs structure are sensitive to the donor thickness while the subband energies and the subband occupations are not sensitive to the donor thickness . PACS 73.20.Dx; 73.20.At; 73.90.+f     

Calculation of critical indices for systems with strong dipole interaction

In ferromagnets and ferroelectrics, dipole interaction reduces critical fluctuations and changes the critical indices. In the present paper the critical indices of susceptibility and specific heat for three-dimensional systems with dipole forces are calculated without taking account of anisotropy. This formulation of the problem has been justified over a wide temperature range for cubic ferromagnets and ferroelectrics of the displacement type where the influence of the cubic anisotropy is small in comparison with the dipole forces. Cubic anisotropy appears in a very small neighborhood of the Curie point, transforming the transition into a phase transition of the first kind [1]. Uniaxial ferromagnets with weak anisotropy also have a dipole region where the anisotropy is significant [2]. The critical indices for systems with dipole interactions in (4-)-dimensional space have been calculated in [3, 4]. The Hamiltonian of a ferromagnet (ferroelectric) without allowance for anisotropy is of the formTranslated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 126–128, October, 1976.The author wishes to thank A. L. Sokolov for formulating the problem.     

Anisotropic in-plane thermal conductivity in multilayer silicene

We systematically study thermal conductivity of multilayer silicene by means of Boltzmann Transportation Equation (BTE) method. We find that their thermal conductivity strongly depends on the surface structures. Thermal conductivity of bilayer silicene varies from 3.31 W/mK to 57.9 W/mK with different surface structures. Also, the $2\times 1$ surface reconstruction induces unusual large thermal conductivity anisotropy, which reaches 70% in a four-layer silicene. We also find that the anisotropy decreases with silicene thickness increasing, owing to the significant reduction of thermal conductivity in the zigzag direction and its slight increment in the armchair direction. Finally, we find that both the phonon-lifetime anisotropy and the phonon-group-velocity anisotropy contribute to the thermal conductivity anisotropy of multilayer silicene. These findings could be helpful in the field of heat management, thermoelectric applications involving silicene and other multilayer nanomaterials with surface reconstructions in the future.     

Neutral current in the heavy top quark limit and the renormalization of the singlet axial current

We use a simple renormalization group argument to demonstrate that the large top mass limit of the axial neutral current in QCD is unambiguously determined by the renormalization of the singlet axial current which suggests a natural scheme independent normalization condition for the latter. By calculating the anomalous dimension of the singlet axial current at three-loop level in the scheme we derive the result for the top quark decoupling from the axial neutral current valid up to (and including) the terms of order _s ² .Work supported by DFG Grant Nr. Ku 502/3-1     

Influence of the surface anisotropy on the ground state of thin ferromagnetic films

A study is made of the ground state of a ferromagnetic film with a surface anisotropy which varies within wide limits from the easy-plane to the easy-axis type (– < 4) and with a bulk anisotropy of the easy-axis type ( 4). A rigorous analytic solution of the problem is given. The formulas obtained make it possible to calculate the distribution of the magnetization across the thickness of the film as a function of the parameters of the system. It is shown that there are two phase transitions from an inhomogeneous to a homogeneous state.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 71–76, July, 1980.The authors are grateful to B. A. Ivanov for his valuable comments and discussion of the results obtained.