Electron tunneling in the GaAs/AlAs(111) structures with a smooth potential at heteroboundaries

The effect of smooth interface potential on the electron tunneling in the GaAs/AlAs(111) structures with thin layers is studied using the pseudopotential method. The transition region between the structure components is represented by a half-period of the hexagonal (GaAs) ₃(AlAs)₃ (111) superlattice. It is shown that the allowance for the smooth potential results in a decrease in the Γ-L-mixing, Fano-resonance narrowing, and disappearance of interface states at the GaAs/AlAs(111) interface as compared to the abrupt-interface model. The shifts of the lowest Γ-and L-resonances observed for the structures with the layer thickness <2 nm amount to ∼0.1 eV, which is in good agreement with the behavior of levels in quantum wells. The transmission coefficient of electrons with the energies 0–0.5 eV above the GaAs conduction-band bottom obtained by multivalley calculation is close to that calculated with allowance for the lowest conduction band states Γ ₁ ⁽¹⁾ and Γ ₁ ⁽²⁾ of superlattice and Γ ₁ and L ₁ of binary crystals. This indicates that a two-valley superlattice model of the smooth GaAs/AlAs(111) interface can be developed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 7–13, July, 2007.     

Structural analysis of the Γ phase in cholesterol-distearoylphosphatidylcholine multilamellar vesicles

Summary The interaction of cholesterol with membranes is particularly interesting as the cholesterol concentration influences membrane stability and permeability by inducing changes in the structure and dynamics of the constituent lipid molecules. On the other hand, cholesterol is present in the atherosclerotic plaques and in some skin diseases, like xanthomas and xantelasmas. An investigation was performed on the Γ phase in a cholesterol-distearoyl phosphatidyl choline (DSPC) mixture by using X-ray diffraction and differential scanning calorimetry. The cholesterol/DSPC molar ratio was 35/65 and DSPC-to-water weight ratio was 1/3. The Γ phase appears at sufficiently high concentration of cholesterol and it is characterized by interchain positional order considerably lower than in theL _β′ andP _β′ phases but higher than in theL _∝ liquid crystalline phase of pure lecithin in excess water. The results suggest that a lateral phase separation exists in the temperature range of existence of the Γ phase. The other phase Γ′ appears to be richer in cholesterol. The (Γ+Γ′) toL _∝ phase transition was investigated and the temperature dependence of the in-plane correlation length in the Γ phase was determined. A very weak enthalpy peak was observed at the chain melting transition, confirming the highly disordered nature of phases Γ and Γ′. Work presented at the First USSR-Italy Bilateral Meeting on Liquid Crystals held in Portonovo, Ancona (Italy), September 30–October 2, 1987.     

Tachyon warm-inflationary universe model in the weakly dissipative regime

The warm-inflationary universe model in a tachyon field theory is studied in the weakly dissipative regime. We develop our model for an exponential potential and the dissipation parameter Γ=Γ ₀=constant. We describe scalar and tensor perturbations for this scenario.     

The shape of an axisymmetric bubble in uniform motion

We consider in a frame fixed to a bubble translating with steady speedU, the inviscid, axisymmetric, irrotational motion of the liquid past it. If all speeds are normalized byU and lengths by {ie437-1}, whereT is the surface tension of the liquid-bubble interface, it can be shown that the unknown bubble shape and field depend on a single parameter {ie437-2} alone, where the pressures are the ones in the bubble and far away respectively. WhenΓ is very large the bubble is almost spherical in shape while for Γ<- Γ^* ≈ -0.315, bubbles whose exteriors are simply connected do not exist. We solve the non-linear, free boundary problem for the whole range Γ^* < Γ < ∞ by the use of an analytical representation for the bubble shape, a surface singularity method to compute potential flows and a generalized Newton’s method to continue inΓ. Apart from providing explicit representations for bubble shapes and detailed numerical values for the bubble parameters, we show that the classical linearized solution for largeΓ is a very good approximation, surprisingly, to as low values of Γ as 2. We also show that Miksiset al [1] is inaccurate over the whole range and in serious error for large and smallΓ. These have been corrected.     

Intervalley electron scattering by phonons in (AlAs)1(GaAs)3(001) superlattices

Intervalley electron scattering by phonons in (AlAs)₁(GaAs)₃(001) superlattices is studied using the pseudopotential method and a phenomenological model of the bonding forces. The deformation potentials between the conduction band extrema of the superlattice involving short-and long-wavelength phonons are calculated. It is shown that the mixing of states from the zinc-blende L valleys plays a greater role in intervalley scattering in a superlattice than the Γ-X mixing. In particular, due to L-L mixing, the Γ-X ₃ transitions, analogous to Γ-L transitions in zinc blende, have higher intensities than the analogues of Γ-X transitions (Γ₁-M ₅ and (Γ₁-Γ₃ transitions). The deformation potentials averaged over the scattering channels in the superlattice agree with the corresponding potentials in a solid solution, but all transitions in the superlattice have higher intensities for the lower states.     

Electronic properties of multinary alloys

Summary A model version of the coherent-potential approximation (CPA) is outlined to evaluate the fundamental energy gapsΓ _15v -Γ _1c ′,Γ _15v -L _1c ,Γ _15v -X _1c of a multinary solid solution. A comparison of theoretical results with the transition energy values obtained from direct interpolation of the corresponding values of ternary alloys is presented for some composition of the solution Al_1−x−y Ga _x In _y As at fixed lattice constants (matching the lattice constants of InP and AlAs). Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

A Generalization of the Stillinger–Lovett Sum Rules for the Two-Dimensional Jellium

In the equilibrium statistical mechanics of classical Coulomb fluids, the long-range tail of the Coulomb potential gives rise to the Stillinger–Lovett sum rules for the charge correlation functions. For the jellium model of mobile particles of charge q immersed in a neutralizing background, the Stillinger–Lovett sum rules give the charge and second moment of the screening cloud around a particle of the jellium. In this paper, we generalize these sum rules to the screening cloud induced around a pointlike guest charge Zq immersed in the bulk interior of the 2D jellium with the coupling constant Γ=β q ² (β is the inverse temperature), in the whole region of the thermodynamic stability of the guest charge amplitude Z>−2/Γ. The derivation is based on a mapping technique of the 2D jellium at the coupling Γ = (even positive integer) onto a discrete 1D anticommuting-field theory; we assume that the final results remain valid for all real values of Γ corresponding to the fluid regime. The generalized sum rules reproduce for arbitrary coupling Γ the standard Z=1 and the trivial Z=0 results. They are also checked in the Debye–Hückel limit Γ→0 and at the free-fermion point Γ=2. The generalized second-moment sum rule provides some exact information about possible sign oscillations of the induced charge density in space.     

Structure of turbulent flows of incompressible fluids and the parametrization of turbulence

The structure of stationary isotropic, homogeneous turbulence in an incompressible fluid with Re ≫ 1 set into motion by a force with amplitude f ₀ and spatial and temporal time scales of r ₀ and τ ₀, respectively, is examined. It is found that, depending on the magnitude of the force that sets the fluid into motion, three fundamentally different turbulent stationary states of the fluid can develop and the dimensionless parameters responsible for transitions from one state to another, γ=f ₀ τ ₀ ² /r ₀ and Γ=γ ^4/3 Re, are determined. It is shown that for γ≪1 and Γ≪1 a Kolmogorov spectrum with E(k)∝1/k ^5/3 develops in the inertial range. During the transition to turbulent flows driven by large amplitude forces f ₀, i.e., during the transition to a regime with γ≪1 and Γ ≫ 1, a segment of the spectrum with E(k)∝1/k ² develops near the viscous range and “detaches” the Kolmogorov spectrum from the viscous range. Further increases in the amplitude f ₀ of the force, i.e., approaching the parameter range with γ≫1 and Γ≫1, causes the entire inertial range to be “occupied” by a spectrum E(k)∝1/k ², and outside the inertial range, large scale structures with a characteristic size extending to γ ^2/5 r ₀ begin to be generated. In the regime with Γ≪1, the power dissipated per unit mass of fluid is independent of the viscosity, but on going to turbulent regimes with Γ≫1, the viscous losses begin to depend on the viscosity of the fluid. The “turn-off” of viscous dissipation for Γ≫1 shows that a drag crisis can occur simply as the source power is increased, without any further conditions. With this method for the excitation of turbulence, the Loitsyanskii integral diverges for arbitrary values of γ and Γ. A physical mechanism is proposed to explain the readjustment of the spectrum of the turbulent fluctuations at different γ and Γ. These results have all been obtained neglecting intermittency. Zh. éksp. Teor. Fiz. 116, 1630–1647 (November 1999)     

Electrical resistivity of noble and transition metals using Animalu's model potential

Calculations of the electrical resistivity of several solid noble and transition metals have been carried out using the transition metal model potential proposed by Animalu. It has been found that, except for Cu, Ag and Au, the calculated resistivities of solid transition metals are considerably below the experimental values indicating that the Animalu's model potential fails to account for the electrical resistivities of transition metals. The failure of the Animalu's model potential has been discussed.     

Phonon dispersion in scandium and yttrium

Phonon dispersion relations for Sc and Y are calculated along [0001] and [01$\text{1}$0] symmetry directions using Animalu transition metal model potential.     

Thermodynamics Properties of the Inner Horizon of?a?Kerr-Newman Black Hole

In this paper, we study the thermal properties of the inner horizon of a Kerr-Newman black hole. By adopting Damour-Ruffini method and the thin film model which is developed on the base of brick wall model suggested by ’t Hooft, we calculate the temperature and the entropy of the inner horizon of a Kerr-Newman black hole. We conclude that the temperature of inner horizon is positive and the entropy of the inner horizon is proportional to the area of the inner horizon. The cut-off factor is same as it in calculation of the entropy of the outer horizon, 90β. In addition, we write the integral and differential Bekenstein-Smarr formula as the parameters of the inner horizon. Then, we discuss that if the contribution of the inner horizon is taken into account to the total entropy of the black hole, the Nernst theorem can be satisfied. At last, We calculate the tunneling rate of the outer horizon Γ₊ and the inner horizon Γ₋. The total tunneling rate Γ should be the product of the rates of the outer and inner horizon, Γ=Γ₊⋅Γ₋. We find that the total tunneling rate is in agreement with the Parikh’s standard result, Γ→exp (ΔS _BH ), and there is no information loss.     

Near-IR laser inelastic electronic light scattering spectroscopy on transitions between ground and excited states of acceptor centers in GaAs and InP crystals

We report the development of a method for recording the low-temperature (T=6 K) near-IR inelastic light scattering spectra and the observation of electronic scattering on the transitions 1s _3/2(Γ₈) → 2s _3/2(Γ₈) between the ground and excited states of different shallow acceptor centers in a n-type semi-insulating crystal si-GaAs (n=1.0 × 10⁸ cm⁻³) and in a doped p-InP crystal (p=3.6×10¹⁷ cm⁻³). Moreover, a new line, associated with the transition 1s _3/2(Γ ₈) → 2p _3/2(Γ₈) and due to a dielectric local mode, recorded for the first time in the spectra of narrow-gap semiconductors, was found in the residual-frequency band in the p-InP spectrum between TO(Γ) and LO (Γ) phonons. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 5, 334–339 (10 March 1998)     

Current-voltage characteristics of SIS structures with localized states in the material of the barrier layer

Elastic resonant tunneling through a single localized state in an insulating layer (I-layer) situated in the constriction zone between two thick superconducting electrodes is investigated theoretically, and the current-voltage characteristic (IVC) of the structure is calculated. The accompanying analysis leads to the prediction that an appreciable current can flow through the structure, not at |eV|=2Δ (Δ is the modulus of the order parameter of the superconducting electrodes) as in the case of an ordinary SIS junction, but at |eV|⩾Δ, and also that the IVC can acquire segments of negative differential resistance in the case of tunneling through a single localized state. Averaging of the IVC over an ensemble of localized states distributed uniformly throughout the volume of the I-layer and with respect to the energy near the chemical potential min the limit Γ₀/Δ≫1 (Γ₀ is the half-width of the resonance line of the localized state) produces a smaller excess current than in a junction of the SNS type. It is shown that the IVC’s exhibit a transition from an excess current to a deficit current as Γ₀ decreases in the high-voltage range. Zh. éksp. Teor. Fiz. 114, 687–699 (August 1998)     

Higgs Boson Decay into Two Gluons and a <Emphasis Type="Italic">Z</Emphasis> Boson

Results for the one-loop calculation of the decay width Γ(H→ggZ) in the standard model with Higgs boson masses in the range 115 GeV<m _H <2m _W are presented. We find that among all the helicity amplitudes contributing to the width only those for which the gluons have the same polarization and the Z is longitudinally polarized contribute in any significant way. The calculation includes all contributions from the second and third generations, and kinematic cuts to enhance the H→ggZ signal. Compared to the width of H→gg, we find Γ(H→ggZ)/Γ(H→gg)≲10⁻⁴.     

Tunneling Effect of Two Horizons from a Reissner-Nordstrom Black Hole

The understanding of possible role played by the inner horizon of black holes in black hole thermodynamics is still somewhat incomplete. By adopting Damour-Ruffini method and the thin film model which is developed on the base of brick wall model suggested by ’t Hooft, we calculate the temperature and the entropy of the inner horizon of a R-N black hole. We conclude that the temperature of inner horizon is positive and the entropy of the inner horizon is proportional to the area of the inner horizon. In addition, the cut-off factor is 90β, which is same in calculation of the entropy of the outer horizon. So, we prove the existence of thermal characters of the inner horizon. Then, we discuss that if the contribution of the inner horizon is taken into account to the total entropy of the black hole, the Nernst theorem can be satisfied. At last, we study the tunneling effect including the inner horizon of the Reissner-Nordstrom black hole. We calculate the tunneling rate of the outer horizon Γ₊ and the inner horizon Γ₋. The total tunneling rate Γ should be the product of the rates of the outer and inner horizon, Γ=Γ₊⋅Γ₋. We find that the total tunneling rate is in agreement with the Parikh’s standard result, Γ→exp (ΔS _BH ), and there is no information loss.     

Appearance of resonant Γ-X mixing in gradient GaAs/AlAs short-period superlattices

We have experimentally investigated the low-temperature (10 K) luminescence and reflection spectra of a gradient GaAs/AlAs superlattice. We have examined the behavior of phonon satellites in the vicinity of the X-Γ resonance. Smooth passage through the resonance was achieved by scanning an exciting light beam along the surface of a gradient sample. Based on our experimental results, we have determined the functional dependence of the Γ-X mixing potential on the resonance detuning. Fiz. Tverd. Tela (St. Petersburg) 40, 822–823 (May 1998)     

A large sample study of spin relaxation and magnetometric sensitivity of paraffin-coated Cs vapor cells

We have manufactured more than 250 nominally identical paraffin-coated Cs vapor cells (28 mm inner diameter bulbs) for multi-channel atomic magnetometer applications. We describe our dedicated cell characterization apparatus. For each cell we have determined the intrinsic longitudinal, Γ ₀₁, and transverse, Γ ₀₂, relaxation rates. Our best cell shows Γ ₀₁/2π≈0.5 Hz, and Γ ₀₂/2π≈2 Hz. We find a strong correlation of both relaxation rates which we explain in terms of reservoir and spin exchange relaxation. For each cell we have determined the optimal combination of rf and laser powers which yield the highest sensitivity to magnetic field changes. Out of all produced cells, 90% are found to have magnetometric sensitivities in the range of 9 to 30 fT . Noise analysis shows that the magnetometers operated with such cells have a sensitivity close to the fundamental photon shot noise limit.     

Spontaneous-emission spectrum in a cavity: Doublet or triplet?

Summary The Green’s functions formalism together with the new algorithm in operating with ζ-functions has been used to obtain the three-peaked spectrum of spontaneous emission of an atom in a weakly damped cavity. The single-peaked spectrum and exponential decay law with the short (τ_s ~ 1/Γ _c) and long (τ₁ ~Γ _c/g ²) decay times have been shown to exist in the strongly damped cavity with its passive linewidthΓ _c.     

The quenching of nucleon yields in the nonmesonic weak decay of Λ -hypernuclei and the three-body weak decay process

Recent exclusive coincidence measurements of non-mesonic weak decays (NMWD) reported for the ratio of the partial decay width of neutron-induced-to-proton-induced NMWD, Γ_n/Γ_p , values of 0.45±0.11±0.03 and 0.51±0.13±0.04 for 5lam and ¹² _Λ C , respectively. These observations agree well with the improved theoretical Γ_n/Γ_p ratios which are in the range of 0.3-0.7. It appears that the long-standing discrepancy between the experimental and theoretical values of Γ_n/Γ_p has finally been solved. However, when compared to the results of intra-nuclear cascade (INC) calculations, the observed numbers of both single nucleons and coincident nucleon pairs are strongly quenched. The quenching of the proton yield observed previously has been interpreted as an increase of the Γ_n/Γ_p ratio. On the other hand, significant contributions from the two-nucleon-induced three-body process ΛNN → nNN are predicted. Indeed, the angular correlation of the emitted nucleon pairs in the NMWD of ¹² _Λ C showed not only decay events in back-to-back kinematics, but also events with non-back-to-back kinematics. In this paper we show that the difficulties to extract the correct Γ_n/Γ_p ratio from the proton spectra is related to the three-body weak-interaction process which strongly quenches the nucleon yields.     

Dimers on Surface Graphs and Spin Structures. II

In a previous paper [3], we showed how certain orientations of the edges of a graph Γ embedded in a closed oriented surface Σ can be understood as discrete spin structures on Σ. We then used this correspondence to give a geometric proof of the Pfaffian formula for the partition function of the dimer model on Γ. In the present article, we generalize these results to the case of compact oriented surfaces with boundary. We also show how the operations of cutting and gluing act on discrete spin structures and how they change the partition function. These operations allow to reformulate the dimer model as a quantum field theory on surface graphs.