Effect of symmetry of the electron states of HTSC on the current-voltage characteristics of SIS junctions

The current-voltage (IV) characteristics of SIS junctions are calculated in the framework of a multiband model with an anisotropic effective order parameter of HTSC. The results of calculations show that the shape of the IV characteristic and of the density of electron states changes significantly depending on the parameters of the model. A theoretical explanation is proposed for the experimentally observed s-like behavior of the IV characteristics of SIN and SIS junctions with BSCCO-type superconductors. The dependence of the superconducting peak asymmetry on the mutual arrangement of the bands is analyzed. The difference between the obtained results and the results of one-band models with the s and d symmetries of the order parameter is discussed.     

Heavy doping effects on donor-acceptor spectra of polar semiconductors at low temperatures

The heavy doping effects on donor-acceptor (DA)-pair spectra at small DA-pair distances R are investigated, basing on an effective screened impurity potential model given by Morgan and on the results of the R-dependent electron (hole)—longitudinal optical phonon interaction energy obtained by Kartheuser et al. It is suggested that the deviation of the electron—hole recombination energy by dense impurities (or at small R), found from the energy of the emitted photon for a zero-phonon transition, results from the band-gap narrowing effect.At large R, we have found that the energy gap of the pure ZnSe crystal is equal to 2.827 eV, in good agreement with observed results. Finally, at small R, our numerical results applied to ZnSe doped with ln and Li impurities are compared with other theories and with observed results.     

Prediction of the attenuation of road traffic noise with distance

A method is described of calculating the sound pressure level received from single, representative light and heavy vehicles after propagation over terrain composed of various combinations of hard ground and grass-land. These results are then used to derive correction contours for the attenuation with distance of the L_eq level received from streams of each class of vehicle. The results apply to conditions where the boundary between the soft and hard areas is parallel to the traffic stream and the soft ground is on the receiver side. Various positions of the boundary are considered. A simple prediction method for L_eq is developed, incorporating the distance corrections. Similar calculations are carried out for the attenuation with distance of the L₁₀ noise index for a representative stream of vehicles. Based on these results simple prediction equations for the excess attenuation are proposed in terms of the receiver position and the proportion of soft ground below the propagation path.     

Effects of finite size and shape on scattering and thermodynamic quantities at 2D Ising critical points

Using recent results by Cardy based on the conformal invariance of critical correlation functions we calculate universal results for scattering functions S(k), susceptibilities, correlation lengths and specific heat correction terms for finite Ising systems in two dimensions with circular and rectangular shapes and free boundary conditions. Our results specify the effect of shape on these quantities at the critical point. In particular, the half-width and lineshape of the scattering function is found to be strongly influenced by geometry. For a circle, S(k) follows the infinite system behavior 1/k^2−η, η = 0.25 only for very large k. For a substantial range of intermediate k values it is well represented by 1/k^2−η_app, with an “apparent” exponent η_app. We also discuss the probable influence of end, edge and domain wall effects on the correlation lengths, susceptibilities and specific heat correction terms. The application of our results to experimental systems and other theoretical models is considered.     

Green function method study of the anisotropic ferromagnetic Heisenberg model on a square lattice

We study the phase diagram of the anisotropic ferromagnetic Heisenberg model on a square lattice. We use the double-time Green’s function method within the Callen decoupling approximation. The dependence of the Curie temperature T_c on the spin S and on the anisotropy parameter Δ (Δ=0 and 1 correspond to the isotropic Heisenberg and Ising model, respectively) is obtained explicitly. Our results are in agreement with results obtained from other theoretical approaches.     

Improvement of a quantum monte carlo method

Quantum Monte Carlo simulations based on the Trotter formula exp(−βH)= lim_M→∞[exp(−gbA/M)exp(−gbB/M)]^M, H=A+B, involve extrapolating the finite M results to the M=∞ limit. New ways to perform this extrapolation are discussed. Data from an older simulation are reanalysed with the new method. For the one-dimensional isotropic ferromagnet our results now agree with other results in the literature. For the one-dimensional isotropic antiferromagnet, the critical exponent of the staggered susceptibility is consistent with 1.     

Two Types of Electronic States in One-Dimensional Crystals of Finite Length

Exact and general results on the electronic states in one-dimensional crystals bounded at τ and τ+L, where L=Na, N is a positive integer, and a is the potential period, are presented. Corresponding to each energy band of the Bloch wave, there are N−1 states in the finite crystal whose energies are dependent on L but not on τ and map the energy band exactly. There is always one and only one electronic state corresponding to each band gap of the Bloch wave, whose energy is dependent on τ but not on L. This state is either a constant-energy confined band-edge state or a surface state in the band gap.     

Asymptotics of the cross section of the electron loss by fast ions in light media

The dependence of the single electron loss cross section on the nuclear charge Z of a projectile and on the nuclear charge Zt of a target atom for fast collisions is studied theoretically using the plane-wave Born approximation and the sum rule. The results of calculations for fast singly and triply charged ions show that the single electron loss cross section increases monotonically as Z and Zt increase. This can be used to interpolate cross sections of processes if there are no experimental data. The results of calculations compare with the experimental and theoretical data of other authors.     

Monte Carlo simulation of a confined hard ellipse fluid

The structural and thermodynamic properties of a confined hard ellipse fluid are studied using Monte Carlo simulation. The angular, average number densities and order parameters of hard ellipses confined between hard parallel walls are obtained for various bulk densities, aspect ratios and wall separations. The results show that the effect of the existence of the wall on the molecular fluid structure, either on their directions or their locations, with respect to the bulk, especially close to the walls, is significant. For this system the pressure is also obtained and it is shown that the average density at the wall is proportional to the pressure, βP=〈ρ_w〉. Our simulation results show that the order parameters depend on the number of the particles in the box unless it exceeds thousand.     

Symplectic large-N theory of topological heavy-fermion semiconductors

The electronic properties of three different oxides (ZnO, SnO₂ and SiO₂) are investigated within many-body perturbation theory in the G ⁰ W ⁰ approximation. The frequency dependence of the dielectric function is either approximated using two different well-established plasmon-pole models (one of which enforces the fulfillment of the f-sum rule) or treated explicitly by means of the contour-deformation approach. Comparing these results, it is found that the plasmon-pole model enforcing the f-sum rule gives less accurate results for all three oxides. The calculated electronic properties are also compared with the available experimental data and previous ab initio results, focusing on the d state binding energies. The G ⁰ W ⁰ approach leads to significantly improved band gaps with respect to calculations based on the density functional theory in the local density approximation.     

GeneralizedM-diffusion model of molecular rotations

The widely usedM-model of rotational diffusion of molecules in fluid phases is generalized. The ordinaryM-model assumes that intermolecular collisions causeinstantaneous changes in the orientation of an otherwise free rotor. The present scheme takes cognizance of the ubiquitous intermolecular torques which should make the molecular orientation a continuously variable random function of time. It is assumed here that the component of the angular velocity, which is conjugate to the angle specifying the orientation of the molecule, is a stationary Gaussian-Markov process. The ordinaryM-model emerges then as a special case of the more general treatment presented here. The results derived for the dipole correlation function of a linear rotor on the basis of the generalized scheme are applied to a series of infrared data. The observed agreement is highly satisfactory. The present analysis affords a justification for the Gordon scheme which generalizes theM-model by assigning to the mean rate of collision anad-hoc dependence on the angular speed of the rotor. It is argued also that the model treated here incorporates certain memory effects which are ignored in the ordinaryM-model, and may yield, in some cases, results which are similar to those based on certain memory function formalisms.     

The role of isospin on the N=Z line

The role played by isospin in nuclear structure phenomena encountered on the N=Z line is discussed. New results on Coulomb energy differences (CED) at high spin for odd-A nuclei in the f _7/2 shell are presented and interpreted in the framework of a simple Cranked Shell Model treatment involving an exact numerical diagonalisation. Results for the CED between the A=46 even-even mirror pairs are also discussed. The CED between the T=1 states in N=Z odd-odd nuclei and their isobaric analogues are suggested as a possible probe of np pairing on the N=Z line. First results from a numerical diagonalization of IBM-4 are cited.     

Linear polarization studies of the high-resolution absorption spectrum of palladiumporphin

The results of linear polarization measurements on the vibronic bands in the S₁ ← S₀ absorption spectrum of palladiumporphin (PdP) are reported. The experiments have been performed at 1.2 K on single crystals of dilute solutions of PdP in n-octane, n-nonane, and n-decane. The symmetries of a number of bands are assigned. From a comparison of the results with those found for the free base porphin it is concluded that the crystal field has a relatively high effective symmetry and that the optical transition moments run through pairs of opposite nitrogen atoms. The manifestation in the polarized absorption spectra of different sites is discussed. It is finally shown that the 180-cm^?1 Jahn-Teller active vibration in zincporphin has b_1g symmetry.     

Interpretation of the photoemission spectrum of chemisorbed carbon monoxide on Ni (100)

Cluster model calculations suggest that the molecular orbitals of CO are significantly perturbed upon chemisorption on Ni. The CO-Ni interaction is found to involve the Ni-d electrons in addition to the s-and p-derived states, contrary to some earlier suggestions. Based on our results, a new interpretation is proposed for the observed photoemission spectra of CO on Ni, which is consistent with the large bonding and relaxation shifts in other systems.     

On some low-temperature properties of (La, Ce)B6 alloys

Some recent experimental data on the magnetic susceptibility and the low-temperature magnetization of the (La, Ce)B₆ system are discussed in the light of the theoretical results. A value of the s-f exchange constant J is estimated which is also consistent with the results obtained from both the Kondo effect and the RKKY interaction.     

Analytical approach to the Curie temperature Tc(S,d) of spin-S Ising model on d-dimensional hypercubic lattice

An effective mean-field theory based on cumulant expansion (EMFC) is applied to the spin-S Ising model on general d-dimensional hypercubic lattice. It gives straightforwardly the analytical expressions T_c^(ν)(S,d) that approach the Curie temperature order by order. For general d, the results up to fifth order are given. Numerical results up to seventh order for d=2,3,4 are presented.     

Rayleigh scattering fromn=3 states of hydrogenlike atoms

An exact analytic evaluation of the Kramers-Heisenberg matrix elements for Rayleigh scattering fromn=3 states of hydrogenlike atoms is performed in the nonrelativistic dipole approximation, using the Green's function method. The results are given separately for each subshell. The possibility of 3s?3d transitions is also considered. The dependence on the photon energy is contained in six invariant amplitudes. The formulas needed for the evaluation of the various cross sections are presented. The numerical results are contained in tables from which partial and total cross sections can be easily built, covering the energy range from zero up to 20 times theK threshold energy. In the vicinity of Balmerα frequency the cross section is large and comparable with that for excitedn=2 states, confirming an earlier hypothesis of Röhr. At other energies the cross sections forn=2 andn=3 states are comparable, too. The results should be useful in plasma diagnostics.     

Implications of an ionic model of SiO2

As a test of an ionic model of SiO₂, we have computed the silicon Kβ and L_2,3 X-ray emission bands using ionic wave functions for idealized β-cristobalite and results from an earlier tight-binding fit to the valence bands. Good agreement with experiment is obtained except for a high energy feature in the L_2,3 spectrum. It is noted that the “ionic” O^2? wave functions are very diffuse and have considerable amplitude on neighboring sites. Orthogonalization to silicon s and p cores leads to 3s and 3p-like behavior about the silicons; however, there is no d core to orthogonalize to, so the d-like behavior about the silicons is not properly described. Some explict 3d admixture appears necessary to describe the upper L_2,3 feature. The Compton scattering results of Rosenberg et al. are discussed in the context of our results.