scholarly journals Analytical study of holographic superconductors with exponential nonlinear electrodynamics

2016 ◽  
Vol 94 (12) ◽  
pp. 1372-1377 ◽  
Author(s):  
A. Sheykhi ◽  
F. Shaker
Keyword(s):  
Critical Temperature ◽  
Mean Field Theory ◽  
Mean Field ◽  
Nonlinear Electrodynamics ◽  
Analytical Relation ◽  
De Sitter ◽  
S Wave ◽  
Holographic Superconductors ◽  
Sturm Liouville ◽  
Good Agreement

Based on the Sturm–Liouville eigenvalue problem, we analytically study several properties of holographic s-wave superconductors with exponential nonlinear (EN) electrodynamics in the background of Schwarzschild anti-de Sitter black holes. We assume the probe limit in which the scalar and gauge fields do not back react on the background metric. We show that for this system, one can still obtain an analytical relation between the critical temperature and the charge density. Interestingly enough, we find that EN electrodynamics decreases the critical temperature, Tc, of the holographic superconductors compared to the linear Maxwell field. This implies that the nonlinear electrodynamics make the condensation harder. The analytical results obtained in this paper are in good agreement with the existing numerical results. We also compute the critical exponent near the critical temperature and find out that it is still 1/2, which seems to be a universal value in mean field theory.

scholarly journals SUPERCONDUCTIVITY IN THE 2D ATTRACTIVE HUBBARD MODEL WITHIN A FUNCTIONAL FIELD-THEORETICAL RG

2011 ◽  
Vol 25 (28) ◽  
pp. 3691-3706 ◽  
Author(s):  
EBERTH CORREA ◽  
HERMANN FREIRE ◽  
ALVARO FERRAZ
Keyword(s):  
Hubbard Model ◽  
Long Range ◽  
Quantum Monte Carlo ◽  
Mean Field Theory ◽  
Mean Field ◽  
S Wave ◽  
Energy Dynamics ◽  
Attractive Hubbard Model ◽  
Bare Interaction ◽  
Good Agreement

We apply the functional field-theoretical renormalization group methodology up to two-loop order to the 2D attractive Hubbard model for weak bare interaction. Since the momentum-resolved quasiparticle weight ZΛ(p) is always close to unity in the RG flow, higher-order quantum fluctuations do not affect crucially the low-energy dynamics in this case. As a result, we observe a s-wave singlet superconducting quasi-long-range order phase as a function of doping in good agreement with other numerical methods. To assess the role played by the fluctuations we compare the critical temperature Tc in which the quasi-long-range superconducting order phase takes place within our approach with mean-field theory and quantum Monte Carlo results.

scholarly journals HOLOGRAPHIC SUPERCONDUCTORS WITH WEYL CORRECTIONS VIA GAUGE/GRAVITY DUALITY

2013 ◽  
Vol 28 (19) ◽  
pp. 1350096 ◽  
Author(s):  
D. MOMENI ◽  
R. MYRZAKULOV ◽  
M. RAZA
Keyword(s):  
Mean Field Theory ◽  
Mean Field ◽  
P Wave ◽  
Matching Method ◽  
Expectation Value ◽  
Holographic Superconductors ◽  
The Mean ◽  
Gauge Gravity ◽  
Gravity Duality ◽  
Good Agreement

In this paper, we analytically investigate the properties of Weyl's corrected p-wave holographic superconductors by the matching method. The relation between the critical temperature Tc and the charge density ρ has been obtained as Tc ∝ ρ⅓ and the dependence of the expectation value of the condensation operator on the temperature has been found analytically in the form [Formula: see text]. The critical exponent of the condensation also comes out to be ½, which is the universal value in the mean field theory and which has nothing to do with the Weyl coupling γ. Our results are in very good agreement with the existing numerical results and have been obtained using the variational method.

scholarly journals Holographic superconductor with nonlinear Born–Infeld-type electrodynamics

2019 ◽  
Vol 34 (03n04) ◽  
pp. 1950019 ◽  
Author(s):  
S. I. Kruglov
Keyword(s):  
Critical Temperature ◽  
Order Parameter ◽  
Model Parameters ◽  
De Sitter ◽  
S Wave ◽  
Matching Method ◽  
Holographic Superconductor ◽  
Critical Temperatures ◽  
Sturm Liouville ◽  
Analytical Expressions

Holographic s-wave superconductors in the framework of nonlinear Born–Infeld-type electrodynamics are investigated in the background of Schwarzschild anti-de Sitter black holes. As particular cases, at some model parameters, we obtain results for Born–Infeld and exponential electrodynamics. We explore the analytical Sturm–Liouville eigenvalue problem in the probe limit where the scalar and electromagnetic fields do not affect the background metric. The critical temperatures of phase transitions and the order parameter are calculated which depend on the model parameters. We show that the critical exponent near the critical temperature is 1/2. Making use of the matching method, we derive analytical expressions for the condensation values and the critical temperature. The conductivity by the analytical method is calculated.

scholarly journals Effects of backreaction and exponential nonlinear electrodynamics on the holographic superconductors

2016 ◽  
Vol 26 (06) ◽  
pp. 1750050 ◽  
Author(s):  
A. Sheykhi ◽  
F. Shaker
Keyword(s):  
Mean Field ◽  
Nonlinear Electrodynamics ◽  
Gauge Fields ◽  
Holographic Superconductor ◽  
Nonlinear Parameters ◽  
Holographic Superconductors ◽  
Black Hole Background ◽  
Sturm Liouville ◽  
The Mean ◽  
Exponential Nonlinear Electrodynamics

We analytically study the properties of a [Formula: see text]-dimensional [Formula: see text]-wave holographic superconductor in the presence of exponential nonlinear (EN) electrodynamics. We consider the case in which the scalar and gauge fields back react on the background metric. Employing the analytical Sturm–Liouville method, we find that in the black hole background, the nonlinear electrodynamics correction will affect the properties of the holographic superconductors. We find that with increasing both backreaction and nonlinear parameters, the scalar hair condensation on the boundary will develop more difficult. We obtain the relation connecting the critical temperature with the charge density. Our analytical results support that, even in the presence of the nonlinear electrodynamics and backreaction, the phase transition for the holographic superconductor still belongs to the second-order and the critical exponent of the system always takes the mean-field value [Formula: see text].

Magnetic properties of NiAlxFe2−xO4 spinels: A mean field approach and high-temperature series expansions study

2018 ◽  
Vol 32 (07) ◽  
pp. 1850070 ◽  
Author(s):  
S. Salmi ◽  
R. Masrour ◽  
A. El Grini ◽  
K. Bouslykhane ◽  
A. Hourmatallah ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
High Temperature ◽  
Critical Temperature ◽  
Magnetic Measurement ◽  
Mean Field Theory ◽  
Mean Field ◽  
Exchange Interactions ◽  
Temperature Series ◽  
Series Expansions ◽  
Good Agreement

The magnetic properties of NiAl[Formula: see text]Fe[Formula: see text]O4 (NAFO) spinels were studied. Influence of Al doping on magnetic properties of NiFe2O4 spinel were examined. The exchange interactions in NAFO were obtained. The general expression of saturation magnetization and the critical temperature were obtained using mean field theory. The high-temperature series expansions combined with the Padé approximant are given to determine the critical temperature of NAFO. The critical exponent associated with the magnetic susceptibility [Formula: see text] was also deduced. The obtained results were in good agreement with magnetic measurement.

scholarly journals Magnetocaloric Effect in Nanosystems Based on Ferromagnets with Different Curie Temperatures

2021 ◽  
Vol 132 (1) ◽  
pp. 79-93
Author(s):  
M. A. Kuznetsov ◽  
A. B. Drovosekov ◽  
A. A. Fraerman
Keyword(s):  
Field Theory ◽  
Magnetocaloric Effect ◽  
Landau Theory ◽  
Mean Field Theory ◽  
Mean Field ◽  
Maxwell Relation ◽  
Magnetic Cooling ◽  
The Mean ◽  
Curie Temperatures ◽  
Good Agreement

Abstract The magnetocaloric effect in nanosystems based on exchange-coupled ferromagnets with different Curie temperatures is calculated within the mean-field theory. Good agreement between the results of the mean-field theory and the Landau theory, valid near the critical phase transition temperature, is demonstrated for a flat-layered Fe/Gd/Fe structure. We show that a high magnetic cooling efficiency in this system is attainable in principle and prove the validity of the Maxwell relation, enabling an experimental verification of the predictions made. The theory developed for flat-layered structures is generalized to a granular medium.

Bose Liquid Mean-Field Theory with Application to HeI

2019 ◽  
Vol 26 (02) ◽  
pp. 1950005
Author(s):  
Jan Maćkowiak
Keyword(s):  
Field Theory ◽  
Heat Capacity ◽  
Temperature Dependence ◽  
Mean Field Theory ◽  
Mean Field ◽  
Liquid Structure ◽  
Experimental Plot ◽  
Bose Liquid ◽  
Ordered Motion ◽  
Good Agreement

A mean-field theory is developed for a Bose liquid enclosed in a large vessel 𝒱. In accord with liquid structure concepts of Mitus et al., the liquid in 𝒱 is assumed to consist of adjacent macroscopic subregions Λk. In each subregion the bosons perform a locally ordered motion with prevailing orientation k + x, which varies randomly when passing from one subregion to another. |k| is constant, whereas temperature dependence of |x| is governed by a mean-field theory (MFT). The theory is applied to simulate HeI heat capacity CV (T) at T > Tλ = 2.17 K and CV (T) singularity at [Formula: see text]. The MFT numerical heat capacity Cn(T) = ΔE/ΔT exhibits behaviour characteristic of a singularity at [Formula: see text]: rapid increase with decreasing ΔT. Apart from [Formula: see text], good agreement of Cn(T) with CV(T) experimental plot is also found above Tλ, at T ∊ (Tλ, 3K].

scholarly journals Evening out the spin and charge parity to increase $${T}_{c}$$ in $${{\rm{Sr}}}_{2}{{\rm{RuO}}}_{4}$$

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Swagata Acharya ◽  
Dimitar Pashov ◽  
Cédric Weber ◽  
Hyowon Park ◽  
Lorenzo Sponza ◽  
...  
Keyword(s):  
Critical Temperature ◽  
Degrees Of Freedom ◽  
Mean Field Theory ◽  
Mean Field ◽  
Spin Fluctuations ◽  
Charge Fluctuations ◽  
Ab Initio Theory ◽  
Charge Parity ◽  
Local Correlations ◽  
Critical Temperature Tc

AbstractUnconventional superconductivity in $${{\rm{Sr}}}_{2}{{\rm{RuO}}}_{4}$$Sr2RuO4 has been intensively studied for decades. However, the nature of pairing continues to be widely debated. Here we develop a detailed ab initio theory, coupling quasiparticle self-consistent GW approximation with dynamical mean field theory (DMFT), including both local and non-local correlations to address the subtle interplay among spin, charge and orbital degrees of freedom. We report that the superconducting instability has multiple triplet and singlet components. In the unstrained case the triplet eigenvalues are larger than the singlets. Under uniaxial strain, the triplet eigenvalues drop and the singlet components increase. This is concomitant with our observation of spin and charge fluctuations shifting closer to wave-vectors favoring singlet pairing. We identify a complex mechanism where charge fluctuations and spin fluctuations co-operate in the even-parity channel under strain leading to increment in critical temperature (Tc), thus proposing a novel mechanism for pushing the frontier of critical temperature (Tc) in unconventional ‘triplet’ superconductors.

MOTT TRANSITION IN THE HALF-FILLED HUBBARD MODEL ON THE HONEYCOMB LATTICE WITHIN COHERENT POTENTIAL APPROXIMATION

2013 ◽  
Vol 27 (07) ◽  
pp. 1350046 ◽  
Author(s):  
DUC ANH LE
Keyword(s):  
Hubbard Model ◽  
Quantum Monte Carlo ◽  
Mean Field Theory ◽  
Mean Field ◽  
Coulomb Repulsion ◽  
Mott Transition ◽  
Coherent Potential Approximation ◽  
Honeycomb Lattice ◽  
Potential Approximation ◽  
Good Agreement

Using the coherent potential approximation, we study zero-temperature Mott transition in the half-filled Hubbard model on the honeycomb lattice. Although a pseudogap is already present for the non-interacting case, the gap will not occur until the onsite Coulomb repulsion exceeds a critical value U ≈ 3.6t, where t is the hopping integral. When increasing U/t, the density of states at the Fermi energy first goes up gradually from zero and after reaching a maximum it goes down to zero again. Our calculated critical interaction UC/t is in very good agreement with the ones obtained by quantum Monte Carlo simulation and cluster dynamical mean-field theory.

THEORETICAL INVESTIGATION OF ASYMMETRIC SIMPLE EXCLUSION PROCESSES WITH OFF-RAMP ON THE BOUNDARIES

2012 ◽  
Vol 26 (24) ◽  
pp. 1250155 ◽  
Author(s):  
SONG XIAO ◽  
SHUYING WU ◽  
LIQIONG TANG ◽  
DONGSHENG ZHENG ◽  
JING SHANG
Keyword(s):  
Field Theory ◽  
Monte Carlo ◽  
Computer Simulations ◽  
Mean Field Theory ◽  
Mean Field ◽  
Exclusion Processes ◽  
Density Profiles ◽  
Asymmetric Simple Exclusion ◽  
Simple Exclusion ◽  
Good Agreement

In this letter, asymmetric simple exclusion processes with off-ramp on the boundaries have been studied by asymmetric simple exclusion processes (ASEPs). In this model, particles can only detach from a single off-ramp on the boundaries of the system. The phase diagrams and density profiles are calculated by approximate mean field theory and have shown good agreement with the extensive Monte Carlo computer simulations.

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