Influence of impurities on the metallization of inert gases at high pressures

It is shown that the introduction of heavy inert gas impurities into the condensed phase of a lighter inert gas can significantly change the kinetic properties of the latter at high pressures. The electronic structure of the ordered Ar₁₅Xe solid solution is calculated. Doping of the condensed phase of a light inert gas with atoms of a heavier inert gas may become a new convenient tool in high-pressure experiments.     

Variational technique for calculating electron transport using isolated molecules

A variational technique for calculating steady-state nonequilibrium electron transport through an isolated molecule is proposed. It is shown that the Gutzwiller trial variational wave function can be added with an auxiliary variational parameter to satisfy inhomogeneous boundary conditions. The I–V characteristic of a junction in the regime of strong Coulomb correlations is constructed that is in good agreement with the experimental data on nitrosubstituted oligo(phenyleneethynylene) molecules. A strong rise in the correlation amplification of a molecule’s magnetic susceptibility is observed near the peak in the current.     

Magnetization dynamics in isolated Ising chains

The Glauber dynamics of an Ising chain or ring is shown to be determined by two characteristic times: τ₁ for relaxation of the average magnetization per spin and τ₂ for dynamical spontaneous symmetry breaking. An analytical solution for magnetization dynamics in a finite chain with fixed spins at both ends is found by the method of images. This solution is then used to calculate the spin-spin correlation functions for rings and chains. At low temperatures, since τ₁ ? τ₂, there must exist a range of times when the chain is in one of two ordered states.     

Magnetic structure and phase diagram of Sr<Subscript>5</Subscript>Rh<Subscript>4</Subscript>O<Subscript>12</Subscript> frustrated Ising magnet

The magnetic structure of Sr₅Rh₄O₁₂ is based on Ising chains of rhodium ions with a variable valence, Rh³⁺-Rh⁴⁺. The ordering in the chains is assumed to be ferromagnetic. It has been shown that the magnetic structure and phase diagram of Sr₅Rh₄O₁₂ are well described in a model taking into account weak antiferromagnetic interactions between the nearest and next-nearest neighbors on the triangular lattice of ferromagnetic Ising chains. The ground state at low temperatures is the two-sublattice stripe phase; this phase in the magnetic field is transformed to the ferrimagnetic phase and, then, to the ferromagnetic phase. Small plateaus can be observed in the region of the transition from the ferrimagnetic phase to the ferromagnetic one.     

Correlation mechanism of negative differential resistance for tunneling through a molecule

A model for electron transport through a single molecule with two electronic states, one of which is strongly hybridized with contacts and the other is localized, has been investigated. A solution for this model in the limit of strong intramolecular Coulomb interaction is found. A mechanism of negative differential resistance caused by strong intramolecular correlations is revealed.     

Low-energy excitations of Yb As in a magnetic field

We discuss the effects of an applied magnetic field on the low-energy excitations in the low temperature phase of Yb₄As₃. We show also why the magnetic interaction of the Yb³⁺ ions is nearly of an isotropic Heisenberg spin-1/2 type. A small anisotropy due to an intrachain dipolar interaction leads to the opening of a gap when a magnetic field is applied. The model agrees with available experimental data. Simple experiments are suggested in order to further test the present theory. Received 3 February 1999     

Variational model for one-dimensional quantum magnets

A new variational technique for investigation of the ground state and correlation functions in 1D quantum magnets is proposed. A spin Hamiltonian is reduced to a fermionic representation by the Jordan–Wigner transformation. The ground state is described by a new non-local trial wave function, and the total energy is calculated in an analytic form as a function of two variational parameters. This approach is demonstrated with an example of the XXZ-chain of spin-1/2 under a staggered magnetic field. Generalizations and applications of the variational technique for low-dimensional magnetic systems are discussed.     

The ground state of a strongly correlated fermion system in a magnetic field

A new variational method is used to investigate the ground state of the Hubbard model with a half-filled band for a one-dimensional chain, a planar square lattice, and a simple cubic lattice. A metamagnetic transition is found to occur in a one-dimensional chain and a simple square lattice. A simple cubic lattice does not undergo the metamagnetic transition.     

Electronic structure of layered compounds

The electronic structure of the intercalated graphite compounds XC₆ (X = Ca, Sr, Ba, Yb, and La) has been studied using the linearized augmented plane-wave method. It has been found that the electronic structure of the carbon layers in these compounds is qualitatively different from a two-dimensional graphite structure. A lower critical superconducting-transition temperature in YbC₆, as compared with that in CaC₆, at a higher electron density in the carbon layers can be explained by the strong hybridization of the p states of carbon and the d states of ytterbium near the Fermi level. An increase in the critical temperature would be expected in the compounds XC₆ with Group III metals, for example, in LaC₆.     

Steplike magnetization in a spin-chain system:Ca3Co2O6

Because of a ferromagnetic in-chain coupling between Co3+ ions at trigonal sites, Co2O6 chains are considered as large rigid spin moments. The antiferromagnetic Ising model on the triangular lattice is applied to describe an interchain ordering. An evolution of metastable states in a sweeping magnetic field is investigated by the single-flip technique. At the first approximation two steps in the magnetization curve and a plateau at 1/3 of the saturation magnetization are found. Four steps in magnetization are determined in high-order approximations in agreement with experimental results.