Superconductivity in model cuprate as an S=1 pseudomagnon condensation

We make use of the S=1 pseudospin formalism to describe the charge degree of freedom in a model high-$T_c$ cuprate with the on-site Hilbert space reduced to the three effective valence centers, nominally Cu$^{1+,\,2+,\,3+}$. Starting with a parent cuprate as an analogue of the quantum paramagnet ground state and using the Schwinger boson technique we found the pseudospin spectrum and conditions for the pseudomagnon condensation with phase transition to a superconducting state.Comment: Version to be published in JLT

Asymptotics of quasi-classical localized states in 2D system of charged hard-core bosons

The continuous quasi-classical two-sublattice approximation is constructed for the 2D system of charged hard-core bosons to explore metastable inhomogeneous states analogous to inhomogeneous localized excitations in magnetic systems. The types of localized excitations are determined by asymptotic analysis and compared with numerical results. Depending on the homogeneous ground state, the excitations are the ferro and antiferro type vortices, the skyrmion-like topological excitations or linear domain walls.Comment: 5 pages, 2 figure

On closed rotating worlds

A new solution for the stationary closed world with rigid rotation is obtained for the spinning fluid source. It is found that the spin and vorticity are locally balanced. This model qualitatively shows that the local rotation of the cosmological matter can be indeed related to the global cosmic vorticity, provided the total angular momentum of the closed world is vanishing.Comment: 10 pages, Revtex, to appear in Phys. Rev. D6

Nonrelativistic Multiferroicity in the Nonstoichiometric Spin s=1/2 Spiral Chain Cuprate LiCu2O2

We argue for a recently observed puzzling multiferroic behavior in s=1/2 1D chain cuprate LiCu2O2 with edge-shared arrangement of CuO4 plaquettes and incommensurate spiral spin ordering can be consistently explained if one takes into account the nonrelativistic exchange-induced electric polarization on the Cu2+ centers substituting for the positions native for the Cu1+ ions. These substituent centers are proved to be an effective probe of the spin incommensurability and magnetic field effects.Comment: 4 pages, 4 figure

Critical Behavior of a 2D Spin-Pseudospin Model in a Strong Exchange Limit

We study the 2D static spin-pseudospin model equivalent to the dilute frustrated antiferromagnetic Ising model with charge impurities. We present the results of classical Monte Carlo simulation on a square lattice with periodic boundary conditions in a “strong” exchange limit. In the framework of the finite-size scaling theory we obtained the static critical exponents for the specific heat α and the correlation length ν for a wide range of the local density–density interaction parameter ∆ and charge density n. It was shown that the system exhibits non-universal critical behavior depending on these parameters. © 2020 Polish Academy of Sciences. All rights reserved.Russian Foundation for Basic Research, RFBR: 18-32-00837/18Ministry of Education and Science of the Russian Federation, Minobrnauka: 2277, 5719Government Council on Grants, Russian FederationThe research was supported by the Government of the Russian Federation, Program 02.A03.21.0006 and by the Ministry of Education and Science of the Russian Federation, projects No. 2277 and 5719 by RFBR according to the research project No. 18-32-00837/18, scholarship of the president of the Russian Federation No. SP-2278.2019.1

Origin of Magnetoresistance Anomalies in Antiferromagnetic YBa2Cu3O6+x

Specific d-wave angular dependence of the in-plane magnetoresistance in antiferromagnetic tetragonal YBa2Cu3O6+x (x ∼ 0.3) on the orientation of the external magnetic field within the (a,b) plane is assigned to the effective hole transport through the low-lying excited pure oxygen doublet O2peu state in CuO4 plaquette, rather than the ground b1g(dx(2)-y(2)) state. The external magnetic field is believed to determine the orientation of the strong exchange field for the spin-triplet b1geu:3Eu state of the hole CuO4 center and owing to the spin-orbit coupling results in a specific orbital polarization of the Eu doublet. Namely, this gives rise to the spatial d-wave like anisotropy of the hole transport. The experimental data allow to estimate the parameter of the effective spin Hamiltonian. © 2002 Elsevier Science Ltd. All rights reserved.The research described in this publication was made possible in part by CRDF grant No. REC-005. The authors acknowledge a partial support from the Russian Ministry of Education, grant E00-3.4-280, and Russian Foundation for Basic Researches, grant 01-02-96404. One of us (A.S.M.) would like to thank for hospitality Max-Planck Institute für Physik komplexer Systeme and Institut für Festkörper-und Werkstofforschung Dresden where part of this work was made

Lattice Model for water-solute mixtures

A lattice model for the study of mixtures of associating liquids is proposed. Solvent and solute are modeled by adapting the associating lattice gas (ALG) model. The nature of interaction solute/solvent is controlled by tuning the energy interactions between the patches of ALG model. We have studied three set of parameters, resulting on, hydrophilic, inert and hydrophobic interactions. Extensive Monte Carlo simulations were carried out and the behavior of pure components and the excess properties of the mixtures have been studied. The pure components: water (solvent) and solute, have quite similar phase diagrams, presenting: gas, low density liquid, and high density liquid phases. In the case of solute, the regions of coexistence are substantially reduced when compared with both the water and the standard ALG models. A numerical procedure has been developed in order to attain series of results at constant pressure from simulations of the lattice gas model in the grand canonical ensemble. The excess properties of the mixtures: volume and enthalpy as the function of the solute fraction have been studied for different interaction parameters of the model. Our model is able to reproduce qualitatively well the excess volume and enthalpy for different aqueous solutions. For the hydrophilic case, we show that the model is able to reproduce the excess volume and enthalpy of mixtures of small alcohols and amines. The inert case reproduces the behavior of large alcohols such as, propanol, butanol and pentanol. For last case (hydrophobic), the excess properties reproduce the behavior of ionic liquids in aqueous solution.Comment: 28 pages, 13 figure