The Mean Field Bound for the Order Parameter of Bernoulli Percolation

1987 ◽  
pp. 49-71 ◽  
Author(s):  
J. T. Chayes ◽  
L. Chayes
Keyword(s):  
Order Parameter ◽  
Mean Field ◽  
The Mean ◽  
Mean Field Bound

scholarly journals DISORDER INDUCED BCS-BEC CROSSOVER

2012 ◽  
Vol 11 ◽  
pp. 120-126 ◽  
Author(s):  
AYAN KHAN
Keyword(s):  
Order Parameter ◽  
Chemical Potential ◽  
Random Potential ◽  
Mean Field ◽  
Superconducting Order Parameter ◽  
Interesting Issue ◽  
Coupled Equations ◽  
Weak Regime ◽  
The Mean ◽  
Superconducting Fluctuations

Of late, the study of BCS-BEC crossover in the presence of weak random impurity is an interesting issue. In this proceedings we study the effect of this disorder which is included through the Nozières and Smith-Rink theory of superconducting fluctuations. In the weak regime, the random potential leaves an effect on the superconducting order parameter but it spares the chemical potential. Here we present the exact behavior of the mean field quantities as a function of the disorder by self-consistently solving the coupled equations.

CRITICAL DIMENSIONS OF SYSTEMS WITH JOINT MULTICRITICAL AND LIFSHITZ-POINT-LIKE BEHAVIOR

2011 ◽  
Vol 25 (22) ◽  
pp. 1839-1845 ◽  
Author(s):  
ARTEM V. BABICH ◽  
LESYA N. KITCENKO ◽  
VYACHESLAV F. KLEPIKOV
Keyword(s):  
Field Theory ◽  
Critical Phenomena ◽  
Critical Points ◽  
Order Parameter ◽  
Mean Field Theory ◽  
Mean Field ◽  
Critical Dimensions ◽  
Lifshitz Point ◽  
The Mean ◽  
Derivatives Of

In this article, we consider a model that allows one to describe critical phenomena in systems with higher powers and derivatives of order parameter. The systems considered have critical points with joint multicritical and Lifshitz-point-like properties. We assess the lower and upper critical dimensions of these systems. These calculation enable us to find the fluctuation region where the mean field theory description does not work.

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

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.

scholarly journals Multi-mode excitation drives disorder during the ultrafast melting of a C4-symmetry-broken phase

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
Daniel Perez-Salinas ◽  
Allan S. Johnson ◽  
Dharmalingam Prabhakaran ◽  
Simon Wall
Keyword(s):  
Phase Transitions ◽  
Order Parameter ◽  
Landau Theory ◽  
Mean Field ◽  
Atomic Scale ◽  
Time Dependent ◽  
Ginzburg Landau ◽  
Mode Excitation ◽  
The Mean ◽  
Multi Mode

AbstractSpontaneous C4-symmetry breaking phases are ubiquitous in layered quantum materials, and often compete with other phases such as superconductivity. Preferential suppression of the symmetry broken phases by light has been used to explain non-equilibrium light induced superconductivity, metallicity, and the creation of metastable states. Key to understanding how these phases emerge is understanding how C4 symmetry is restored. A leading approach is based on time-dependent Ginzburg-Landau theory, which explains the coherence response seen in many systems. However, we show that, for the case of the single layered manganite La0.5Sr1.5MnO4, the theory fails. Instead, we find an ultrafast inhomogeneous disordering transition in which the mean-field order parameter no longer reflects the atomic-scale state of the system. Our results suggest that disorder may be common to light-induced phase transitions, and methods beyond the mean-field are necessary for understanding and manipulating photoinduced phases.

A FIRST ORDER PHASE TRANSITION IN ISING FERRIMAGNETS

1995 ◽  
Vol 09 (21) ◽  
pp. 1347-1351 ◽  
Author(s):  
HASAN M. AL MUKADAM ◽  
DIMO I. UZUNOV
Keyword(s):  
Phase Transition ◽  
Order Parameter ◽  
Mean Field Theory ◽  
Mean Field ◽  
First Order ◽  
First Order Phase Transition ◽  
Exchange Constants ◽  
The Mean ◽  
First Order Phase ◽  
Ising Spins

The mean field theory is used for the analysis of a two-sublattice system of Ising spins, which describes ferro-, antiferro-, and ferrimagnetic orderings. It is proven that the phase transition in these systems is of a first order when the exchange constants of the sublattices are different. The free energy, the order parameter profiles and the latent heat of the phase transition are calculated for almost equivalent sublattices.

EXCESS CONDUCTIVITY IN THE MEAN FIELD AND PARACOHERENCE REGIMES OF (La1.6Y0.4)Ba2Ca0.8Cu4.8Oz SUPERCONDUCTORS

2006 ◽  
Vol 20 (02n03) ◽  
pp. 111-122 ◽  
Author(s):  
P. K. NAYAK ◽  
S. RAVI
Keyword(s):  
Heisenberg Model ◽  
Order Parameter ◽  
Mean Field ◽  
Excess Conductivity ◽  
Temperature Variations ◽  
Phase Fluctuations ◽  
Higher Temperature ◽  
The Mean ◽  
Breaking Time ◽  
Mean Field Regime

The temperature variations of electrical resistivity have been measured on pure and 5 wt% Ag doped ( La 1.6 Y 0.4) Ba 2 Ca 0.8 Cu 4.8 O z superconductors. These data were analyzed in terms of fluctuation-induced excess conductivity in the mean field regime by using the Aslamazov–Larkin (AL), Lawrence–Doniach (LD) and Maki–Thompson (MT) models. The fluctuations in the amplitude of order parameter are found to be two dimensional in nature in the mean field region. The estimated values of the average phase breaking time τϕ (100 K) are found to be 3.9×10-16 s and 4.6×10-16 s for pure and Ag doped samples respectively. The resistivity data were also analyzed in terms of excess conductivity due to phase fluctuations of the order parameter in the paracoherence region. The critical exponent is found to be mostly comparable to that of the 3D XY ferromagnet in the vicinity of zero resistivity temperature and the diluted Heisenberg model at a higher temperature.

ANTIFERROMAGNETISM AND HOLE CONCENTRATION IN THE LINEAR SPIN WAVE APPROXIMATION OF THE t-J MODEL

1994 ◽  
Vol 08 (02) ◽  
pp. 131-136 ◽  
Author(s):  
A. BELKASRI ◽  
J.L. RICHARD
Keyword(s):  
Spin Wave ◽  
Order Parameter ◽  
Degrees Of Freedom ◽  
Hole Concentration ◽  
Mean Field ◽  
Field Approximation ◽  
Mean Field Approximation ◽  
Antiferromagnetic State ◽  
Wave Approximation ◽  
The Mean

The interplay between antiferromagnetic state and low doping regime is studied within the framework of the t-J model. The staggered magnetization is calculated in the mean field approximation by separating spin and charge degrees of freedom. We have obtained that this order parameter decreases with increasing doping and vanishes for some critical hole concentration.

A QUANTUM SIMULATOR FOR PROBING MOTT LOBES VIA THE AC JOSEPHSON EFFECT

2013 ◽  
Vol 11 (05) ◽  
pp. 1350049
Author(s):  
MING-XIA HUO ◽  
YING LI ◽  
ZHI SONG ◽  
CHANG-PU SUN
Keyword(s):  
Field Theory ◽  
Order Parameter ◽  
Mean Field Theory ◽  
Mean Field ◽  
Finite Size ◽  
Weak Field ◽  
Josephson Current ◽  
Theory Approach ◽  
The Mean ◽  
Quantum Simulator

In this paper, we propose to directly detect Mott lobes, i.e. the order parameter 〈a〉, describing the Mott insulator (MI) to superfluid (SF) quantum phase transition of the Bose–Hubbard (BH) model. By weakly coupling the system to an environment in the SF phase, the U(1) symmetry breaking of the system is simulated, and the order parameter can be read from the AC Josephson current between the system and the environment. The relation between the order parameter and the Josephson current is obtained from both the mean-field theory approach and an exact numerical simulation of a finite-size example. Our numerical simulations show that the profile of the order parameter read from the Josephson current is different from it predicted by the mean-field theory, but similar to it in a system whose U(1) symmetry is broken by a weak field proportional to a + a†. This proposal is feasible in optical lattices.

Calculation of the tilt angle and susceptibility for the α–β transition in quartz using a mean field model

2017 ◽  
Vol 31 (09) ◽  
pp. 1750092 ◽  
Author(s):  
H. Yurtseven ◽  
U. Ipekoğlu ◽  
S. Ateş
Keyword(s):  
Experimental Data ◽  
Phase Transition ◽  
Temperature Dependence ◽  
Tilt Angle ◽  
Phenomenological Model ◽  
Order Parameter ◽  
Field Model ◽  
Mean Field ◽  
Mean Field Model ◽  
The Mean

Tilt angle (order parameter) and the susceptibility are calculated as a function of temperature for the [Formula: see text]–[Formula: see text] transition in quartz using a Landau phenomenological model. The tilt angle as obtained from the model is fitted to the experimental data from the literature and the temperature dependence of the tilt angle susceptibility is predicted close to the [Formula: see text]–[Formula: see text] transition in quartz. Our results show that the mean field model explains the observed behavior of the [Formula: see text]–[Formula: see text] phase transition in quartz adequately and it can be applied to some related materials.

scholarly journals Order parameter effect critical fields and current of Y1–xPrx:123 superconductors

2018 ◽  
Vol 35 (4) ◽  
pp. 838-845
Author(s):  
A. Sedky ◽  
S.A. Amin
Keyword(s):  
Order Parameter ◽  
Mean Field ◽  
Interlayer Coupling ◽  
Critical Fields ◽  
Logarithmic Plot ◽  
The Mean ◽  
Cu Ions ◽  
Coherence Lengths ◽  
Reduced Temperature ◽  
2D To 3D

Abstract Fluctuation induced conductivity by Pr substitution at Y sites of Y1-xPrx:123 superconductors is reported. It is found that the mean field temperature Tcmf, deduced from the peak of dρ/dT versus T plot, gradually decreases by increasing Pr up to 0.40. The order parameter dimensionality (OPD) is estimated from the slope of the logarithmic plot between excess conductivity Δσ and reduced temperature є. Interestingly, the crossover from 2D to 3D is obtained for samples with Pr = 0.00, 0.10 and 0.20, while with increasing Pr up to 0.40, the crossover from 0D to quasi-2D is obtained. On the other hand, the calculated values of interlayer coupling, coherence lengths, critical fields and critical current decrease with increasing Pr up to 0.20, but with the further increase of Pr, up to 0.40, they increase. The hole carriers/Cu ions anisotropy and G-L parameter gradually increase with Pr up to 0.40. Our results are discussed in terms of the effects of Pr substitution at Y site, such as oxygen rearrangements, anisotropy, hybridization and localization of holes in the overdoped region.

Sign in / Sign up

Export Citation Format

Share Document