The phase diagram of the O(4) Higgs-fermion lattice model in the mean field approximation

A model for the description of two-subsystem Heisenberg ferrimagnet with frustrated intersubsystem exchange and competition between exchange interactions in a subsystem is proposed. The conditions of the existence of noncollinear Yafet-Kittel state and partially ordered magnetic structure are investigated. The phase diagram of competition parameter vs temperature is obtained in the mean field approximation. The peculiarities of the succesive magnetic phase transitions are considered.

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A MEAN FIELD STUDY OF THE PHASE TRANSITIONS IN A CLASS OF SYSTEMS WITH COMPLEX ORDER PARAMETERS

International Journal of Modern Physics B ◽

10.1142/s0217979294001688 ◽

1994 ◽

Vol 08 (28) ◽

pp. 3963-3986

Author(s):

EVGENIA J. BLAGOEVA

Keyword(s):

Phase Diagram ◽

Phase Transitions ◽

Order Parameter ◽

Mean Field ◽

Field Approximation ◽

Mean Field Approximation ◽

Unconventional Superconductors ◽

Complex Order ◽

The Mean ◽

Expansion Coefficients

A generalized Landau free energy for a complex order parameter expanded up to sixth-order is investigated using group theoretical arguments and the mean-field approximation. Results for the phase transitions that occur are presented. The phase diagram for all allowed values of the expansion coefficients is constructed with an emphasis placed on the influence of the anisotropy in the order parameter space. The results can be used in discussions of unconventional superconductors and modulated structural and magnetic orderings.

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Inhomogeneous chiral condensates in low-energy color-superconductivity models of QCD

10.21248/gups.62534 ◽

2021 ◽

Author(s):

◽

Philip Lakaschus

Keyword(s):

Phase Diagram ◽

Mean Field ◽

Field Approximation ◽

Chiral Condensate ◽

Dispersion Relations ◽

Mean Field Approximation ◽

Color Superconductivity ◽

Diquark Model ◽

Coexistence Phase ◽

The Mean

This thesis explores the phase diagrams of the Nambu--Jona-Lasinio (NJL) and quark-meson (QM) model in the mean-field approximation and beyond. The focus lies in the investigation of the interplay between inhomogeneous chiral condensates and two-flavor color superconductivity. In the first part of this thesis, we study the NJL model with 2SC diquarks in the mean-field approximation and determine the dispersion relations for quasiparticle excitations for generic spatial modulations of the chiral condensate in the presence of a homogeneous 2SC-diquark condensate, provided that the dispersion relations in the absence of color superconductivity are known. We then compare two different Ansätze for the chiral order parameter, the chiral density wave (CDW) and the real-kink crystal (RKC). For both Ansätze we find for specific diquark couplings a so-called coexistence phase where both the inhomogeneous chiral condensate and the diquark condensate coexist. Increasing the diquark coupling disfavors the coexistence phase in favor of a pure diquark phase. On the other hand, decreasing the diquark coupling favors the inhomogeneous phase over the coexistence phase. In the second part of this thesis the functional renormalization group is employed to study the phase diagram of the quark-meson-diquark model. We observe that the region of the phase diagram found in previous studies, where the entropy density takes on unphysical negative values, vanishes when including diquark degrees of freedom. Furthermore, we perform a stability analysis of the homogeneous phase and compare the results with those of previous studies. We find that an increasing diquark coupling leads to a smaller region of instability as the 2SC phase extends to a smaller chemical potential. We also find a region where simultaneously an instability occurs and a non-vanishing diquark condensate forms, which is an indication of the existence of a coexistence phase in accordance with the results of the first part of this work.

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Modulated Phases on the FCC(110) Surfaces with Adsorbate-Induced Reconstructions

Surface Review and Letters ◽

10.1142/s0218625x03005268 ◽

2003 ◽

Vol 10 (02n03) ◽

pp. 189-194

Author(s):

Min Kang ◽

Makoto Kaburagi

Keyword(s):

Phase Diagram ◽

Monte Carlo ◽

Correlation Function ◽

Nearest Neighbor ◽

Mean Field ◽

Field Approximation ◽

Mean Field Approximation ◽

Modulated Phases ◽

The Mean ◽

Beg Model

We theoretically investigate the fcc(110) surfaces with missing row reconstructions induced by adatoms using the Blume–Emmery–Griffith (BEG) model. In the model, Kij is introduced to denote interactions between surface atoms and Jij to describe interactions between dipoles. The investigation by the mean field approximation has predicted that there appear modulated phases on the surfaces as the next-nearest-neighbor (NNN) and the nearest-neighbor (NN) interactions along the [001] direction become competitive. In this study, Monte Carlo simulations are performed to confirm the prediction. A correlation function defined by concentration operators in wave vector q space is calculated. The results show that the concentration modulations appear. The temperature versus the ratio of the NNN interaction K2 to the NN interaction K1 phase diagram is obtained. The possible features of the modulated phases in experiments are discussed.

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Phase Diagram of the Attractive Kane-Mele-Hubbard Model at Half Filling

Atoms ◽

10.3390/atoms8030058 ◽

2020 ◽

Vol 8 (3) ◽

pp. 58

Author(s):

Zlatko Koinov

Keyword(s):

Phase Diagram ◽

Optical Lattices ◽

Nearest Neighbor ◽

Mean Field ◽

Field Approximation ◽

Mean Field Approximation ◽

Recent Developments ◽

Topological States ◽

Half Filling ◽

The Mean

Motivated by recent developments in the experimental study of ultracold atoms in graphene-like honeycomb optical lattices, we investigate superconductivity of the attractive Kane-Mele-Habbard (KMH) model with the next-nearest-neighbor (NNN) hoping at half filling. The mean-field approximation is used to study the phase diagram which interpolates the trivial and the non-trivial topological states. It is shown that: (a) when the NNN hoping is taken into account, one has to introduce two mean-field gap equations for the two sublattices, instead of a single gap when the NNN hopping is neglected, and (b) in the non-trivial topological region the phase diagram with the NNN hopping is significantly different compared to the phase diagram calculated previously, but without the NNN term. We also discuss the superconducting instability of the attractive KMH model that is driven by condensation of Cooperons.

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Mean-field Solution of the mixed spin-1 and spin-5/2Ising system with different single-ion anisotropies

Baghdad Science Journal ◽

10.21123/bsj.6.4.784-789 ◽

2009 ◽

Vol 6 (4) ◽

pp. 784-789

Author(s):

Baghdad Science Journal

Keyword(s):

Phase Diagram ◽

Ground State ◽

Mean Field ◽

Field Approximation ◽

Mean Field Approximation ◽

Two Dimensional ◽

Ground State Phase Diagram ◽

Mixed Spin ◽

Bogoliubov Inequality ◽

The Mean

The mixed-spin ferrimagnetic Ising system consists of two-dimensional sublattices A and B with spin values and respectively .By used the mean-field approximation MFA of Ising model to find magnetism( ).In order to determined the best stabile magnetism , Gibbs free energy employ a variational method based on the Bogoliubov inequality .The ground-state (Phase diagram) structure of our system can easily be determined at , we find six phases with different spins values depend on the effect of a single-ion anisotropies .these lead to determined the second , first orders transition ,and the tricritical points as well as the compensation phenomenon .

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PHASE DIAGRAM OF TWO-FLAVOR QUARK MATTER: GLUONIC PHASE AT NONZERO TEMPERATURE

Modern Physics Letters A ◽

10.1142/s0217732309030400 ◽

2009 ◽

Vol 24 (09) ◽

pp. 647-658

Author(s):

O. KIRIYAMA

Keyword(s):

Phase Diagram ◽

Quark Matter ◽

Mean Field ◽

Field Approximation ◽

Mean Field Approximation ◽

Nonzero Temperature ◽

Self Consistent ◽

Consistent Manner ◽

Cylindrical Phase ◽

The Mean

The phase structure of neutral two-flavor quark matter at nonzero temperature is studied. Our analysis is performed within the framework of a gauged Nambu–Jona-Lasinio model and the mean-field approximation. We compute the free energy of the gluonic phase (gluonic cylindrical phase II) in a self-consistent manner and investigate the phase transition from the gluonic phase to the 2SC/g2SC/NQ phases. We briefly consider the phase diagram in the plane of coupling strength versus temperature and discuss the mixed phase consisting of the normal quark and 2SC phases.

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New statistical lattice model with double honeycomb symmetry

International Journal of Modern Physics B ◽

10.1142/s0217979214500866 ◽

2014 ◽

Vol 28 (15) ◽

pp. 1450086 ◽

Cited By ~ 3

Author(s):

S. Naji ◽

A. Belhaj ◽

H. Labrim ◽

M. Bhihi ◽

A. Benyoussef ◽

...

Keyword(s):

Ground State ◽

Lattice Model ◽

Present Model ◽

Hexagonal Lattice ◽

Mean Field ◽

Field Approximation ◽

Hexagonal Structure ◽

Mean Field Approximation ◽

Two Dimensional Materials ◽

The Mean

Inspired from the connection between Lie symmetries and two-dimensional materials, we propose a new statistical lattice model based on a double hexagonal structure appearing in the G2 symmetry. We first construct an Ising-1/2 model, with spin values σ = ±1, exhibiting such a symmetry. The corresponding ground state shows the ferromagnetic, the antiferromagnetic, the partial ferrimagnetic and the topological ferrimagnetic phases depending on the exchange couplings. Then, we examine the phase diagrams and the magnetization using the mean field approximation (MFA). Among others, it has been suggested that the present model could be localized between systems involving the triangular and the single hexagonal lattice geometries.

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