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arXiv:2109.12231 · Physics of the Solid State

Phase Diagram of Semi-Hard-Core Bosons on a Square Lattice

V. V. Konev, Yu. D. Panov

Published Sep 1, 2021• 1 citation
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Abstract

Abstract Phase diagrams of charged “semi-hard-core” bosons are studied in the mean field approximation. An increase in the parameter of local correlations is shown to lead to the transformation of the phase diagram of the system from the form characteristic of “hard-core” bosons to the limiting form with a parabolic dependence of the critical temperature of charge ordering on the boson concentration. The evolution between these limiting cases is dependent on the ratio between the model parameters and is accompanied by various effects, such as the change in the phase transition type, the appearance of new order–order transition, and the appearance of new critical points.

DOI
10.1134/s1063783421090195

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Abstract Phase diagrams of charged “semi-hard-core” bosons are studied in the mean field approximation. An increase in the parameter of local correlations is shown to lead to the transformation of the phase diagram of the system from the form characteristic of “hard-core” bosons to the limiting form with a parabolic dependence of the critical temperature of charge ordering on the boson concentration. The evolution between these limiting cases is dependent on the ratio between the model parameters and is accompanied by various effects, such as the change in the phase transition type, the appearance of new order–order transition, and the appearance of new critical points.
We investigated the phase diagrams of a system of charged semi-hardcore bosons in the mean-field approximation. It is shown that an increase in the local correlation parameter leads to the transformation of the phase diagram of the system from the form characteristic of hard-core bosons to the limit form with a parabolic dependence of the critical temperature of the charge ordering on the boson concentration. The evolution between these limiting cases depends on the ratio of the model parameters and is accompanied by various effects, including a change in the type of phase transition, the appearance of new order-order transitions, and the appearance of new critical points.
Abstract Neighboring correlations are considered for a two-dimensional hard-core boson model on square lattice within Bethe approximation for the clusters consisting of two and four nodes. Explicit equations are derived for the determination of critical temperatures of charge and superfluid ordering and their solutions are considered for various ratios of the parameter of between-centers charge correlations to the transfer integral. It is demonstrated that assumption of neighboring correlations for the temperatures of charge ordering results in the appearance of the critical concentration of bosons, which restricts the existence domain of the solutions of charge ordering type. In the case of superfluid ordering with the assumption of neighboring correlations, the critical temperature is reduced up to zero values at half filling. A phase diagram of the hard-core boson model is constructed with the assumption of phase separation within Maxwell construction and it is shown that consideration of neighboring correlations within Bethe approximation quantitatively approximates the form of phase diagram to the results of Monte Carlo quantum method.
The authors consider a model of charged semi-hard-core bosons on a square lattice with possible occupation number ni=0,1,2 {{n}_{i}} = 0,1,2~ni​=0,1,2  at each site. Temperature phase diagrams of the model are obtained using quantum Monte Carlo calculations, and the effect of local charge correlations is studied. It is shown that local charge correlations increase the role of quantum fluctuations in the formation of phase states.
The work considers a model of charged "semi-hard-core" bosons on a square lattice with a possible filling number at each node, ranging from 0 to 2. Temperature phase diagrams of the model are obtained using numerical Monte Carlo quantum simulation methods, and the influence of local charge correlations is examined. Comparison with results from mean-field methods shows that local charge correlations contribute to an increased role of quantum fluctuations in the formation of phase states.
Phase transitions are investigated in the Bose-Fermi-Hubbard model in the mean field and hard-core boson approximations for the case of infinitely small fermion transfer and repulsive on-site boson-fermion interaction.The behavior of the Bose-Einstein condensate order parameter and grand canonical potential is analyzed as functions of the chemical potential of bosons at zero temperature.The possibility of change of order of the phase transition to the superfluid phase in the regime of fixed values of the chemical potentials of Bose-and Fermi-particles is established.The relevant phase diagrams are built.
We determine the finite-temperature phase diagram of the square lattice hard-core boson Hubbard model with nearest neighbor repulsion using quantum Monte Carlo simulations. This model is equivalent to an anisotropic spin-1/2 XXZ model in a magnetic field. We present the rich phase diagram with a first order transition between a solid and superfluid phase, instead of a previously conjectured supersolid and a tricritical end point to phase separation. Unusual reentrant behavior with ordering upon increasing the temperature is found, similar to the Pomeranchuk effect in 3He.