Grzegorz Pawłowski

Publications (3)2.26 Total impact

• Source

  Available from: ArXiv

  Article: On the phase diagram of the zero-bandwidth extended Hubbard model with intersite magnetic interactions for strong on-site repulsion limit

  Szymon Murawski, Konrad Kapcia, Grzegorz Pawłowski, Stanisław Robaszkiewicz
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  ABSTRACT: In this report we have analyzed a simple effective model for a description of magnetically ordered insulators. The Hamiltonian considered consists of the effective on-site interaction (U) and the intersite Ising-like magnetic exchange interaction (J) between nearest neighbors. For the first time the phase diagrams of this model have been determined within Monte Carlo simulation on 2D-square lattice. They have been compared with results obtained within variational approach, which treats the on-site term exactly and the intersite interactions within mean-field approximation. We show within both approaches that, depending on the values of interaction parameters and the electron concentration, the system can exhibit not only homogeneous phases: (anti-)ferromagnetic (F) and nonordered (NO), but also phase separated states (PS: F-NO).
  09/2011;
• Article: Flat histogram Monte Carlo sampling for mechanical variables and conjugate thermodynamic fields with example applications to strongly correlated electronic systems.

  Georg Ganzenmüller, Grzegorz Pawłowski
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  ABSTRACT: We present a general and unifying framework for deriving Monte Carlo acceptance rules which facilitate flat histogram sampling. The framework yields uniform sampling rules for thermodynamic states given by the mechanically extensive variables appearing in the Hamiltonian. Likewise, Monte Carlo schemes which uniformly sample the thermodynamic fields that are conjugate to the mechanical variables can be derived within this framework. We apply these different, yet equivalent sampling schemes to the extended Hubbard model in the atomic limit with explicit electron spin. Results for the full density-of-states, the charge-order parameter distribution, and phase diagrams for different ratios of the on-site Hubbard repulsion and the intersite interaction are presented. A tricritical point at half-filling of the lattice is located using finite-size scaling techniques.
  Physical Review E 10/2008; 78(3 Pt 2):036703. · 2.26 Impact Factor
• Source

  Available from: arxiv.org

  Article: Effects of diagonal disorder on charge density wave and superconductivity in local pair systems

  Grzegorz Pawłowski, Stanisław Robaszkiewicz
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  ABSTRACT: We analyse the influence of diagonal disorder (random site energy) on charge density wave (CDW) and superconductivity (SS) in local pair systems which are described by the model of hard core charged bosons on a lattice. This problem was previously studied within the mean field approximation for the case of half-filled band (n=1). Here we extend that investigation to the case of arbitrary particle concentration (0<n<2) and examine the phase diagrams of the model and the behaviour of superfluid density (ρs) as a function of n and the increasing disorder. Depending on the strength of random on-site energies, the intersite density–density repulsion and the concentration, the model can exhibit several various phases, including homogeneous phases: CDW, SS and Bose-glass (NO) as well as the phase separated states: CDW–SS, CDW–NO and particle droplets. The obtained results for SS phase are in qualitative agreement with the available Monte-Carlo calculations for two-dimensional lattice.Also, in a definite range of parameters, the system exhibits the phenomena which we call a disorder induced superconductivity and a disorder induced charge ordering.
  Physica A: Statistical Mechanics and its Applications.