The Ground-State Phase Diagram of 2D Spin–Pseudospin System

Panov, Yu. D.; Moskvin, A. S.; Chikov, A. A.; Budrin, K. S.

doi:10.1007/s10909-017-1743-9

Cited by 23 publications

(29 citation statements)

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“…In the limit ∆ → −∞ it reduces to the S = 1 2 Ising model with fixed magnetization. At ∆ > 0 the results can be compared with the Blume-Capel model [27,28,29] or with the Blume-Emery-Griffiths model [30].An analysis of the ground state (GS) phase diagrams was done within the mean field approach [24,25]. It was shown, that the five GS phases are realized in two limits.…”

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confidence: 99%

Phase diagrams of a 2D Ising spin-pseudospin model

Panov

Ulitko

Budrin

et al. 2019

Journal of Magnetism and Magnetic Materials

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We consider the competition of magnetic and charge ordering in high-Tc cuprates within the framework of the simplified static 2D spin-pseudospin model. This model is equivalent to the 2D dilute antiferromagnetic (AFM) Ising model with charged impurities. We present the mean-field results for the system under study and make a brief comparison with classical Monte Carlo (MC) calculations. Numerical simulations show that the cases of strong exchange and strong charge correlation differ qualitatively. For a strong exchange, the AFM phase is unstable with respect to the phase separation (PS) into the charge and spin subsystems, which behave like immiscible quantum liquids. An analytical expression was obtained for the PS temperature.The Hamiltonian of the static spin-pseudospin model is:where S zi is a z-projection of the on-site pseudospin S = 1 and σ zi = P 0i s zi /s is a normalized z-projection of conventional spin s = 1/2 operator, multiplied by the projection operator P 0i = 1 − S 2 iz . The ∆ = U/2 is the on-site correlation and V > 0 is the inter-site density-density interaction, J =J/s 2 > 0 is the Cu 2+ −Cu 2+ Ising spin exchange coupling, h =h/s is the external magnetic field, µ is the chemical potential, so we assume the total charge constraint, nN = S zi = const, where n is the density of doped charge. The sums run over the sites of a 2D square lattice, ij means the nearest neighbors. This spin-pseudospin model generalizes the 2D dilute AFM Ising model with charged impurities. In the limit ∆ → −∞ it reduces to the S = 1 2 Ising model with fixed magnetization. At ∆ > 0 the results can be compared with the Blume-Capel model [27,28,29] or with the Blume-Emery-Griffiths model [30].An analysis of the ground state (GS) phase diagrams was done within the mean field approach [24,25]. It was shown, that the five GS phases are realized in two limits. In a weak exchange limit, atJ < V , all the GS phases (COI, COII, COIII, FIM) correspond to the charge ordering (CO) of a checker-board type at mean charge density n. While the COI phase is the charge-ordered one without spin centers, the COII and COIII phases are diluted by the non-interacting spins distributed in one sublattice only. This ferrimagnetic spin ordering is a result of the mean-field approach, so the classical MC calculations show a paramagnetic response at low temperatures. The FIM phase is also formally ferrimagnetic. Here the AFM spin ordering is diluted by the non-interacting charges distributed in one sublattice. In a strong exchange limit, atJ > V , there are only COI phase and AFM phase with the charges distributed in both sublattices. The absence of charge transfer in the Hamiltonian (1) is the most important limitation of our present model for comparison with the actual phase diagram of cuprates. But, as shown in [31], the accounting for two-particle transport enriches the GS phase diagram of the spin-pseudospin model with superfluid and supersolid phases competing with CO phases.The paper is organized as follows. We present the mean-field result...

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confidence: 99%

Phase diagrams of a 2D Ising spin-pseudospin model

Panov

Ulitko

Budrin

et al. 2019

Journal of Magnetism and Magnetic Materials

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“…The MFA analysis [3] gives five GS solutions or phases of spin-pseudospin system. The energies and structural characteristics in terms of the on-site charge and spin densities for these phases are given in Table I.…”

Section: The Modelmentioning

confidence: 99%

“…In cuprates, the competition of static magnetic order, bulk superconductivity and charge-density waves has attracted a lot of attention over the years, but its nature remains a challenge [1]. Earlier we suggested a simplified static 2D spin-pseudospin model [2,3] which takes into account both conventional Heisenberg spin exchange coupling and the on-site and inter-site charge correlations. A detailed qualitative and quantitative analysis of the spincharge competition within the model with the ground state (GS) and temperature phase diagrams was done in the mean field approximation (MFA).…”

Section: Introductionmentioning

confidence: 99%

Phase Separation in the Ground State of the Model 2D Spin-Pseudospin System

et al. 2018

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We addressed a simplified static 2D spin-pseudospin model which takes into account both conventional Heisenberg spin exchange coupling and the on-site and inter-site charge correlations. Classical Monte-Carlo calculations for large square lattices show that homogeneous ground state solutions found in a mean-field approximation are unstable with respect to phase separation with the charge and spin subsystems behaving like immiscible quantum liquids. For instance, with lowering the temperature one can observe two sequential phase transitions: first, antiferromagnetic ordering in the spin subsystem diluted by randomly distributed charges, then, the charge condensation in the charge droplets. Thermodynamic properties and phase diagram of the 2D spin-pseudospin system are studied by Monte-Carlo simulation with a special attention given to the role played by the on-site correlation.

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Section: The Modelmentioning

confidence: 99%

“…In cuprates, the competition of static magnetic order, bulk superconductivity and charge-density waves has attracted a lot of attention over the years, but its nature remains a challenge [1]. Earlier we suggested a simplified static 2D spin-pseudospin model [2,3] which takes into account both conventional Heisenberg spin exchange coupling and the on-site and inter-site charge correlations. A detailed qualitative and quantitative analysis of the spin-charge competition within the model with the ground state (GS) and temperature phase diagrams was done in the mean field approximation (MFA).…”

Section: Introductionmentioning

confidence: 99%

Unconventional phase separation in the model 2D spin-pseudospin system

et al. 2018

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Abstract. The competition of charge and spin orderings is a challenging problem for strongly correlated systems, in particular, for high-T c cuprates. We addressed a simplified static 2D spin-pseudospin model which takes into account both conventional spin exchange coupling and the on-site and inter-site charge correlations. Classical Monte-Carlo calculations for large square lattices show that homogeneous ground state antiferromagnetic solutions found in a mean-field approximation are unstable with respect to phase separation into the charge and spin subsystems behaving like immiscible quantum liquids. In this case, with lowering of a temperature one can observe two sequential phase transitions: first, antiferromagnetic ordering in the spin subsystem diluted by randomly distributed charges, then, the charge condensation in the charge droplets. The inhomogeneous droplet phase reduces the energy of the system and changes the diagram of the ground states. On the other hand, the ground state energy of charge-ordered state in a mean-field approximation exactly matches the numerical Monte-Carlo calculations. The doped charges in this case are distributed randomly over a system in the whole temperature range. Various thermodynamic properties of the 2D spin-pseudospin system are studied by Monte-Carlo simulation.

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The Ground-State Phase Diagram of 2D Spin–Pseudospin System

Cited by 23 publications

References 4 publications

Phase diagrams of a 2D Ising spin-pseudospin model

Phase diagrams of a 2D Ising spin-pseudospin model

Phase Separation in the Ground State of the Model 2D Spin-Pseudospin System

Unconventional phase separation in the model 2D spin-pseudospin system

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