Interplay of superconductivity and antiferromagnetism in SmRh4B4

A microscopic theory of interplay of superconductivity and antiferromagnetism in rare earth ternary systems is developed from first principles for less than half filledf atomic shells. Self consistent equations for the superconducting order parameter Δ and magnetic order parameter Γ, are derived using a Green’s function technique and equation of motion method. The theory is applied to explain the experimental results in the antiferromagnetic superconductor SmRh₄B₄. The present model explains true coexistence of superconductivity and antiferromagnetism and the suppression of superconductivity by antiferromagnetism. The behaviour of superconducting order parameter (Δ), magnetic order parameter (Γ), the specific heat, the density of states, free energy and critical field (H _c) is also studied for the system SmRh₄B₄.     

Persistence of superconductivity in magnetically ordered SmRh4B4

Measurements of the thermal conductivity and the electrical resistivity between 50 mK and 4 K in zero magnetic field and in fields exceeding the superconducting critical field H_c2 indicate the persistance of bulk superconductivity in magnetically ordered SmRh₄B₄.     

Magnetic field dependence of the neutron scattering from ErRh4B4

Magnetism in the reentrant superconductor ErRh₄B₄ has been studied by neutron scattering as a function of an applied magnetic field. For a temperature of 1.69 K long-range ferromagnetism is found in fields higher than 1 kOe. Considerable hysteresis is found in the neutron scattering intensity vs magnetic field curve and long-range order with a small Er moment remains when the field is reduced to small values.     

Elastic scattering of B on B in the energy range from 4 to 15 MeV

Angular distributions (at E_c.m. = 4, 6.5 and 10.5 MeV) and excitation functions (at 30°, 60° and 90°) are given for the elastic scattering of ¹⁰B on ¹⁰B. The results of an optical model (OM) analysis are presented and discussed. In the energy range covered the Sommerfeld parameter η varies from 4.4 to 2.3.     

On the range of the nucleon-antinucleon interaction

The range of theN¯N interaction is re-examined. We find that differences in theN¯N models do have an influence on the region where annihilation predominantly takes place. AN¯N model derived consistently within meson theory leads to an annihilation range around 1 fm in spite of the small Compton wavelength of the exchanged baryons usually advocated in range arguments.     

Pion-nucleus interaction and the range of πN forces

We examine several definitions for the ranges r_πN of the pion-nucleon (πN) forces and conclude that 0.25 ≦ r_πN ≦ 0.5 fm. We investigate two consequences of the finite range of the p-wave πN interaction: the additional spatial extension of the p-wave π-nucleus optical potential and the quenching of the Lorentz-Lorenz effect. For 0.25 ≦ r_πN ≦ 0.5 fm (i) the additional extension of the p-wave optical potential gives negligible contributions to shifts and widths in π-mesic atoms and (ii) the Lorentz-Lorenz effect is largely quenched making nuclear correlations hard to detect by mesic atoms measurements.     

Finite interaction range spin glass in the Ising model

Using the Ising model and the random-field approximation, it is demonstrated that, in amorphous diluted magnets and crystalline metal alloys, the nearest neighbor interaction promotes a superparamagnetic state, which is followed by “freezing” of the magnetic moments of clusters and by transition into a macrospin glass state (cluster spin glass) as the temperature decreases. A theoretical magnetic phase diagram is constructed.     

Triplet exciton energy and the magnitude of the charge-transfer interaction inside dimers in the Alkali-TCNQ salts

The optical absorption spectra of several crystalline anion radiacal salts have been analyzed recently within the frame of the model Hamiltonian of electrons and intramolecular excitons and vibrations in the limit of strong interaction of the excitonic and vibrational motions with the unpaired electrons. In the present work the magnitude of the intermolecular charge transfer interaction inside dimers in the Alkali TCNQ salts is deduced from the knowledge of the experimental triplet exciton energy and the constants characterizing the electronic, excitonic and vibrational properties of TCNQ molecules. Perturbation calculation is used to derive a formula for the triplet exciton energy.     

Optical properties of Nd3+ pairs in LiYF4-existence of a short range interaction

Optical studies of Bridgman grown LiYF₄ crystals weakly doped with Nd³⁺ have been made in the vicinity of the ⁴I_9/2→⁴G_5/2 transition. By selective excitation with a narrow pulsed laser or with a CW monomode laser, excitation spectra and dynamical characteristics of infrared and ultraviolet (up-converted) fluorescences produced by satellites associated with Nd³⁺ pairs have been obtained. From the results, an assignment of the satellites to the various classes of pairs has been possible. The existence of a short range interaction, probably superexchange, has been proved which confirms previous observations in another fluoride compound, LaF₃.     

Effect of head-tail ratio and the range of the head-head interaction in amphiphilic self-assembly

We investigate cluster autocorrelations, critical micelle concentration (CMC), and size distribution for amphiphiles of the type H_xT_y as a function of the amphiphilic factor α = for a fixed length l = x + y using a combination of reptation and kink-jump Monte Carlo (MC) moves in a two-dimensional (2D) square lattice. We find that the CMC decreases monotonically as a function of the α-parameter. For a fixed chain length l of the molecule, the symmetric molecules of the type H_l/2T_l/2 with α = 1 tend to form circular micelles with relatively narrow distribution in cluster sizes. As we decrease the α-parameter to introduce head-tail asymmetry, the size distribution becomes polydisperse with occurrences of more elongated micelles. A calculation of the cluster autocorrelation function reveals that for the same chain length, symmetric amphiphiles take significantly less time to equilibrate and therefore simulation of much longer molecules is possible. Next we study the effect of the head-head repulsion term beyond next nearest neighbors. In general, the presence of a longer-range repulsive interaction reduces the average size of the micelles. We also notice that for l = 5, while H₂T₃ molecules produces spherical micelles, the H₁T₄ molecules( α = 0.25) often form vesicles. Our systematic studies bring out relevant information for controlling shapes and sizes of micelles to be used as templates in the design of self-assembled nanostructures.     

Effective range analysis of low-energy nucleon-antinucleon interaction

An effective range expansion is developed for the N$\text{N}$ system incorporating annihilation, charge-exchange and Coulomb interaction. By fitting the LEAR data on elastic scattering and charge-exchange differential cross sections the N$\text{N}$ scattering lengths and effective ranges are obtained. These solutions reproduce also the data on antiprotonic hydrogen, antineutron-proton total and annihilation cross sections and the behavior of the forward amplitude real-to-imaginary ratio.     

Investigation of GaAs Schottky barrier diodes in the THz range

The properties of GaAs Schottky barrier diodes as video detectors and mixing elements were investigated in the frequency range from 0.8–2.5 THz. For the most sensitive diode, the video responsivity and system noise temperature were measured as a function of incident laser power. The highest video responsivity was 2,000 V/W at 214m and 60 V/W at 118m. For five diodes differing in doping, capacitance, series resistance and anode diameter, the system noise temperature was measured at 214m and 118m. The best single sideband (SSB) values are 12,300 K and 24,200 K at 214m and 118m, respectively. The system noise temperature versus frequency is given over the range from 0.5–3 THz for two specific diodes demonstrating that the sharpness of the I–V characteristics is only of secondary importance for mixer perfomance at such high frequencies.     

Short range order and the development of long range order in Ni4Mo

The short-range ordered structure present in quenched Ni₄Mo and the initial development of the long-range-ordered structure have been studied using single crystal X-ray diffuse scattering techniques. Measurements of the diffuse X-ray intensities were made in a volume in reciprocal space for the f.c.c. alloy resulting in a quantitative determination of the three dimensional local-order parameters. The local-order parameters were used for a computer simulation of the atomic configuration.The local atomic arrangements for the quenched alloy consist of a strong preference for no molybdenum atom pairs as first neighbors. The atoms tend to satisfy the long-range-ordered structure of Ni₄Mo in which there are no Mo-Mo pairs as first neighbors, only one Mo atom as second neighbors and six or more as third neighbors. A rodlike morphology consisting of a strong preference for 200 and 400 Mo-Mo pairs exists on ordering for 5 min at 650°C. This result is similar to the rodlike morphology present in dilute Ni-W alloys and explains the [100] streaking of the short-range order peaks observed in the diffraction studies.     

Scaling of dynamics with the range of interaction in short-range attractive colloids

We numerically study the dependence of the dynamics on the range of interaction Delta for the short-range square well potential. We find that, for small Delta, dynamics scale exactly in the same way as thermodynamics, both for Newtonian and Brownian microscopic dynamics. For interaction ranges from a few percent down to the Baxter limit, the relative location of the attractive-glass line and the liquid-gas line does not depend on Delta. This proves that, in this class of potentials, disordered arrested states (gels) can be generated only as a result of a kinetically arrested phase separation.     

The need for long range components in the effective nuclear interaction

It is shown that if one uses single particle energies from experiment and a delta residual interaction it is not possible to obtain the energy of the giant dipole and spurious states of ²⁰⁸Pb, and at the same time obtain reasonable results for the low lying two-particle spectra of ²¹⁰Pb or ²¹⁰Po. Related to the above problem, the isobaric analog state of ²⁰⁸Pb (in ²⁰⁸Bi) comes much too low in calculations using realistic interactions. It is noted here that the above difficulties can be overcome, phenomenologically at least, by adding to the effective interaction some long range repulsive components. The Bansal-French and the Schiffer interactions are examples of these. However, the dipole-dipole component of the Schiffer interaction gives much too large a splitting between the dipole state and spurious state.     

Effects of long range Coulomb interaction on the Peierls instability

The Peierls instability is studied for a one-dimensional tight-binding model of conduction electrons in the half-filled case. The long range Coulomb interaction as well as the electron-phonon coupling are taken into account. It is found that the Peierls distortion is hindered by the long wavelength charge fluctuations due to the Coulomb interaction.     

One-dimensional relativistic motion of two bodies with a constant magnitude of the interaction force

The relativistic linear motion of two bodies with a constant magnitude of the interaction force is considered. Inelastic and elastic collisions of these bodies are investigated. A mathematically exact model of the relativistic oscillator is constructed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 66–69, July, 1982.