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The S = 1 pseudospin formalism was recently proposed to describe the charge degree of freedom in a model high-Tc cuprate with the on-site Hilbert space reduced to the three effective valence centers, nominally Cu1+;2+;3+. With small corrections the model becomes equivalent to a strongly anisotropic S = 1 quantum magnet in an external magnetic field. We have applied a generalized mean-field approach and quantum Monte-Carlo technique for the model 2D S = 1 system to find the ground state phase with its evolution under deviation from half-filling and different correlation functions. Special attention is given to the role played by the on-site correlation ("single-ion anisotropy"). [ABSTRACT FROM AUTHOR]

A theoretical analysis and a large amount of experimental data indicate that the structure of the valence hole states in doped cuprates is more complicated than assumed in the simple Zhang-Rice singlet model. In fact, we are dealing with a competition between a hybrid Cu 3d-O 2p b1g∝dx2-y2-state and purely oxygen nonbonding states with a2g- and eux,y∝px,y-symmetries. Thus, as a cluster analog of a Cu3+ ion, the ground state of a non-Zhang-Rice CuO45- hole center of this sort should be described by complicated 1A1g-1,3B2g-1,3Eu multiplet with a set of charge, orbital, and spin order parameters, some of which are well known (e.g., spin moment or 'ferromagnetic' Ising orbital momentum localized on oxygen ions) while others are unconventional or hidden (e.g., 'antiferromagnetic' ordering of Ising orbital momenta localized on four oxygen atoms or a combined spin-orbital-quadrupole ordering). The non-Zhang-Rice CuO45- centers are actually singlet-triplet pseudo-Jahn-Teller centers with strong vibron coupling to the lattice. The complicated structure of the ground-state multiplet of the hole centers shows up in many of the unusual properties of doped cuprates, in particular, their pseudo-gap phase. [ABSTRACT FROM AUTHOR]

Nominally electron doped antiferromagnetic tetragonal nonsuperconducting Nd2 – xCexCuO4 + δ(x=0.12) has been shown to manifest strong angular dependence of the in-plane magnetoresistance on the orientation of the external magnetic field within the ab plane in many aspects similar to that observed in hole doped YBa2Cu3O7 – δ and La2 – xSrxCuO4. Specific fourfold angular magnetoresistance anisotropy amounting to several percents was observed in oxygen annealed films at low temperatures and in an external magnetic field up to 5.5 T. The strong temperature dependence and fourfold symmetry observed in our sample points to a specific role of rare-earth (Nd) ions in magnetoresistance anisotropy. At low temperature T = 1.4 K, we observed the unusual transformation of magnetoresistance response with increasing the external magnetic field, which seems to be a manifestation of a combined effect of a crossover between first and second order spin-flop transitions and a field-dependent rare-earth contribution to quasiparticle magnetotransport. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

The main mechanism in homogeneous broadening and relaxation of crystal-field excitations for R-ions in cuprates is believed to be provided by the fluctuations of crystalline electric field induced by a static and dynamic charge inhomogeneity generic to doped cuprates. Such an inhomogeneity is assumed to be the result of topological phase separation. We address the generalized granular model as one of the model scenarios for describing the static and dynamic charge inhomogeneity in cuprates. The charge subsystem is believed to be similar to that of a Wigner crystal with melting transition and phononlike positional excitation modes. We consider a simple model of charge inhomogeneity that allows us to elucidate the main universal features of the density of CF states and the respective inhomogeneous broadening. The formal description of R-ion relaxation mainly coincides with that of the recently suggested magnetoelastic mechanism by Lovesey and Staub. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

A new approach to the study of phase separation in lanthanum manganites is proposed based on the combined investigation of their optical and magnetooptical characteristics providing information about the conducting and ferromagnetic regions, respectively. Effects of the [sup 18]O isotope substitution for [sup 16]O in the epitaxial films of (La[sub 0.5]Pr[sub 0.5])[sub 0.7]Ca[sub 0.3]MnO[sub 3] (grown on SrTiO[sub 3] or LaAlO[sub 3] substrates) upon the IR absorption spectra and the equatorial Kerr effect measured in the 1.5–3.8 eV range were studied. A giant drop in the temperature of maximum resistance of the film grown on SrTiO[sub 3] and disappearance of the metal-insulator transition in the film on LaAlO[sub 3] , observed upon the isotope exchange, are accompanied by a decrease in the contribution of free charge carriers to the absorption spectra, by the appearance of bands due to localized states, and by a decrease in magnitude of the equatorial Kerr effects. Measurements of the Kerr effect and the temperature variation of the optical transmission show evidence of the presence of ferromagnetic metal regions in the [sup 18]O-isotope-substituted (La[sub 0.5]Pr[sub 0.5])[sub 0.7]Ca[sub 0.3]MnO[sub 3]/LaAlO[sub 3] film at low temperatures, with a general semiconductor character of the resistivity behavior in the entire temperature range studied. Changes observed in the absorption spectra are explained based on a model of the pseudo-Jahn–Teller polar centers and phase separation. The optical and magnetooptical data show evidence of a percolation nature of the giant isotope effect in manganites. © 2001 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The High Energy Cosmic Ray Observatory (HERO) is an experimental design for the direct study of cosmic rays based on the use of an ultraheavy ionization calorimeter. The effective geometric factor of the facility will be at least 12 m sr for cosmic-ray protons and at least 16–20 m sr for nuclei and electrons. During 5–7 years of exposure, this mission will allow measuring the energy spectra of all common and rare cosmic-ray nuclei in the energy range of eV/particle with element-by-element resolution of the charge of nuclei and with sufficiently high energy resolution. It is planned to study not only the cosmic ray nuclei with charges , but also the superheavy nuclei beyond the iron peak, as well as high-energy electrons, positrons, and gamma rays. The main objectives, design appearance, and characteristics of the space mission are discussed. [ABSTRACT FROM AUTHOR]

The aim of the NUCLEON space experiment was to measure spectra of high-energy cosmic rays. Direct measurements of energy spectra of protons and nuclei of cosmic rays which allow separating particles in charge are required to solve important astrophysical problems. The satellite was launched on December 26, 2014, and operated for three years. Measured spectra of protons and alpha particles in the energy range of 2–500 TeV per particle have been presented. The results have been analyzed and compared to other experimental data for lower energies. The ratio of fluxes of protons and alpha particles is nearly constant in a wide range of magnetic rigidities (3–100 TV). Thus, the behavior of the ratio of the spectra is significantly different from a similar dependence in the region of lower magnetic rigidities measured in other experiments. One of the possible explanation of this effect can be given within a model with one close source. [ABSTRACT FROM AUTHOR]