Asymmetric phases in the mean-field theory of the axial next-nearest-neighbor Ising model

1991 ◽  
Vol 43 (10) ◽  
pp. 8487-8490 ◽  
Author(s):  
Carlos S. O. Yokoi
Keyword(s):  
Field Theory ◽  
Ising Model ◽  
Nearest Neighbor ◽  
Mean Field Theory ◽  
Mean Field ◽  
The Mean

scholarly journals MEAN-FIELD TRANSITION TEMPERATURE OF STRONGLY DISORDERED SUPERCONDUCTORS

2000 ◽  
Vol 14 (06) ◽  
pp. 575-587 ◽  
Author(s):  
IGOR F. HERBUT
Keyword(s):  
Field Theory ◽  
Transition Temperature ◽  
Nearest Neighbor ◽  
Mean Field Theory ◽  
Mean Field ◽  
Localized States ◽  
Effective Theory ◽  
The Mean ◽  
Field Transition ◽  
Infinite Range

I discuss the mean-field theory of superconductivity in a strongly disordered system of fermions with short-range attraction. It is argued that in this limit the effective theory at low energies is equivalent to the disordered Bose–Hubbard model, and I consider both the infinite-range and the "nearest-neighbor" hopping of bosons between the localized states. In the infinite-range case the mean-field theory is exact, and the superconducting gap is uniform in space, while in the latter case, the gap becomes highly non-uniform in space, but, surprisingly, is finite everywhere at T < T MF . I find that the mean-field transition temperature T MF > 0 always, and argue that the superconductor–insulator transition at T = 0 in models with net attraction between fermions is in the universality class of "dirty-bosons".

Tricritical phenomena in an Ising model with nearest- and next-nearest-neighbor interactions

1977 ◽  
Vol 55 (13) ◽  
pp. 1125-1133 ◽  
Author(s):  
M. Plischke ◽  
D. Zobin
Keyword(s):  
Field Theory ◽  
High Temperature ◽  
Ising Model ◽  
Nearest Neighbor ◽  
Tricritical Point ◽  
Mean Field Theory ◽  
Mean Field ◽  
Temperature Series ◽  
Bcc Lattice ◽  
Ferromagnetic Interactions

We report on the analysis of low and high temperature series for the Ising model with nearest-neighbor antiferromagnetic and next-nearest-neighbor ferromagnetic interactions on the bcc lattice. The high temperature series are complete to β7, the low temperature series to u37. We determine the phase diagram, locate the tricritical point, and estimate the tricritical exponents. The tricritical exponents are only in fair agreement with the predictions of tricritical mean field theory.

scholarly journals Evidence of exactness of the mean-field theory in the nonextensive regime of long-range classical spin models

2000 ◽  
Vol 61 (17) ◽  
pp. 11521-11528 ◽  
Author(s):  
Sergio A. Cannas ◽  
A. C. N. de Magalhães ◽  
Francisco A. Tamarit
Keyword(s):  
Field Theory ◽  
Long Range ◽  
Mean Field Theory ◽  
Mean Field ◽  
Spin Models ◽  
Classical Spin ◽  
The Mean ◽  
Classical Spin Models

Mean field theory of the orientational properties of (J = 1) hydrogen molecules on the surface of Grafoil

1979 ◽  
Vol 57 (11) ◽  
pp. 1852-1869 ◽  
Author(s):  
A. B. Harris ◽  
A. J. Berlinsky
Keyword(s):  
Field Theory ◽  
Model Comparison ◽  
Nearest Neighbor ◽  
Mean Field Theory ◽  
Computer Calculation ◽  
Mean Field ◽  
Free Energy Calculations ◽  
Axially Symmetric ◽  
Hydrogen Molecules ◽  
Ordered Phases

A mean field theory is developed which is applicable to the orientational behavior of (J = 1) hydrogen molecules on the surface of Grafoil. The hydrogen molecules are assumed to form a triangular lattice in a weak, axially symmetric crystal field, Vc. perpendicular to the substrate and to interact via the electric quadrupole–quadrupole interaction with nearest-neighbor coupling constant Γ. Free energy calculations for the various possible ordered phases are presented, and a Landau expansion is used to investigate the phase boundary between the disordered and ordered phases. A computer calculation, based on the iterative method of James, is used to determine the lines of transition between ordered phases. For almost all values of Vc < 22.5Γ, the disordered to ordered state phase transition is continuous. Four distinct types of ordered phases are found — a four-sublattice phase, two two-sublattice phases, and a one-sublattice phase which resembles an X–Y model. Comparison is made to the recent nmr data of Kubik and Hardy for H2 and D2 on Grafoil.

On the mean-field theory of spin glasses

1980 ◽  
Vol 13 (3) ◽  
pp. 403-418 ◽  
Author(s):  
A Blandin ◽  
M Gabay ◽  
T Garel
Keyword(s):  
Field Theory ◽  
Spin Glasses ◽  
Mean Field Theory ◽  
Mean Field ◽  
The Mean
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