Holographic superconductors in IR modified Hořava–Lifshitz gravity

2016 ◽  
Vol 31 (19) ◽  
pp. 1650110 ◽  
Author(s):  
Jun-Wang Lu ◽  
Ya-Bo Wu ◽  
Jian Xiao ◽  
Cui-Juan Lu ◽  
Mo-Lin Liu
Keyword(s):  
Phase Transition ◽  
Energy Gap ◽  
Landau Theory ◽  
Mean Field Theory ◽  
Mean Field ◽  
Superconducting Phase ◽  
Ginzburg Landau ◽  
Holographic Superconductors ◽  
The Mean ◽  
Second Order Phase Transition

In the probe limit, we study the holographic [Formula: see text]- and [Formula: see text]-wave superconductors in the IR modified Hořava–Lifshitz gravity and obtain the effect of the gravity parameter [Formula: see text] on the condensate and the AC conductivity. Concretely, for the two models, the increasing [Formula: see text] makes the superconductor phase transition more difficult. Moreover, at the critical point, both systems undergo a second-order phase transition as expected from the mean field theory, and the superfluid density decreases with the temperature linearly, which is consistent with the Ginzburg–Landau theory. Meanwhile, the analytical results back up the numerical results. What is more, in the superconducting phase, the ratio of the energy gap to the critical temperature, i.e. [Formula: see text], decreases with the increasing [Formula: see text]. In addition, our results generalize the previous work on holographic superconductors in Hořava–Lifshitz gravity to some extent.

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.

FLUCTUATION EFFECTS IN A CLASS OF SYSTEMS WITH TWO ORDER PARAMETERS

1993 ◽  
Vol 07 (27) ◽  
pp. 1725-1731 ◽  
Author(s):  
L. DE CESARE ◽  
I. RABUFFO ◽  
D.I. UZUNOV
Keyword(s):  
Phase Transition ◽  
Renormalization Group ◽  
Phase Transitions ◽  
Order Phase Transition ◽  
Mean Field ◽  
Ising Models ◽  
Order Parameters ◽  
The Mean ◽  
Fluctuation Effects ◽  
Second Order Phase Transition

The phase transitions described by coupled spin -1/2 Ising models are investigated with the help of the mean field and the renormalization group theories. Results for the type of possible phase transitions and their fluctuation properties are presented. A fluctuation-induced second-order phase transition is predicted.

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.

Critical Behavior of Gd5Si2Ge1.9Ga0.1 near the Ferromagnetic-Paramagnetic Phase Transition

2013 ◽  
Vol 873 ◽  
pp. 855-860 ◽  
Author(s):  
Zeng Ru Zhao ◽  
Gao Feng Wang ◽  
Xue Feng Zhang
Keyword(s):  
Phase Transition ◽  
Critical Behavior ◽  
Scaling Law ◽  
Mean Field Theory ◽  
Mean Field ◽  
Entropy Change ◽  
Paramagnetic Phase ◽  
Range Type ◽  
Fisher Model ◽  
The Mean

The critical behavior near the ferromagnetic-paramagnetic phase transition in Gd5Si2Ge1.9Ga0.1 has been investigated using a method based on the field dependence of isothermal entropy change. The reliability of the critical exponents determined in such a way has been examined through various techniques, like constructing the modified Arrott plot, applying the scaling law on the isothermal magnetization curves, and comparing the values with those obtained from the Kouvel-Fisher model. The resulting values of the exponents were estimated to be = 0.45(2), = 1.31(5), = 3.9(2) and = 0.69(1), close to the values predicted by the mean field theory. Hence, we concluded that the exchange interaction is of long-range type.

scholarly journals Modeling the Magnetocaloric Effect of Nd0.67Ba0.33Mn0.98 Fe0.02O3 by the Mean Field Theory

2020 ◽  
Author(s):  
Mohamed Hsini ◽  
Sadok Zemni
Keyword(s):  
Field Theory ◽  
Phase Transition ◽  
Magnetic Properties ◽  
Magnetic Fields ◽  
Magnetocaloric Effect ◽  
Mean Field Theory ◽  
Mean Field ◽  
Entropy Change ◽  
Magnetization Curves ◽  
The Mean

In this paper, we have exploited the mean field theory combined with the Bean-Rodbell model to justify the magnetocaloric effect (MCE) in Nd0.67Ba0.33Mn0.98Fe0.02O3 sample. The simulation of some magnetic properties has been investigated. Modeling magnetization curves have been successfully achieved using this model. The second-order ferromagnetic-paramagnetic (FM-PM) phase transition of our system has been verified through the value of the parameter which controls the transition nature in the Bean-Rodbell model. Theoretical and experimental expressions, which have rated the magnetic entropy change ( − ∆ S M ) under various magnetic fields, have been derived. Theoretical ( − ∆ S M ) curves have been compared to the experimental ones.

scholarly journals Multiphase Organization Is a Second Phase Transition Within Multi-Component Biomolecular Condensates

2021 ◽  
Author(s):  
Konstantinos Mazarakos ◽  
Huan-Xiang Zhou
Keyword(s):  
Phase Transition ◽  
Mean Field Theory ◽  
Mean Field ◽  
Individual Species ◽  
Second Phase ◽  
Dense Phase ◽  
Main Driver ◽  
The Mean ◽  
Dynamics Simulations ◽  
The Individual

We present a mean-field theory for the multiphase organization of multi-component biomolecular condensates and validate the theory by molecular dynamics simulations of model mixtures. A first phase transition results in the separation of the dense phase from the bulk phase. In a second phase transition, the components in the dense phase demix to localize in separate regions that attach to each other. The second phase transition occurs when the strength of cross- species attraction goes below the mean strength of the self-attraction of the individual species and reaches a critical value. At a given strength of cross-species attraction, both of the phase transitions can be observed by decreasing temperature, leading first to phase separation and then to demixing of the dense phase. The theory and simulations establish the disparity in strength between self and cross-species attraction as a main driver for the multiphase organization of multi-component biomolecular condensates.

scholarly journals Quantum Mechanics and Superconductivity in a Magnetic Field

1993 ◽  
Vol 46 (3) ◽  
pp. 333 ◽  
Author(s):  
AH MacDonald ◽  
Hiroshi Akera ◽  
MR Norman
Keyword(s):  
Magnetic Field ◽  
Quantum Mechanics ◽  
Magnetic Fields ◽  
Landau Theory ◽  
Mean Field Theory ◽  
Mean Field ◽  
Point Of View ◽  
Ginzburg Landau ◽  
Accurate Picture ◽  
The Individual

The influence of a magnetic field on superconductivity is usually described either phenomenologically, using Ginzburg-Landau theory, or semiclassically, using Gor'kov theory. In this article we discuss the influence of magnetic fields on the mean-field theory of the superconducting instability from a completely quantum-mechanical point of view. The suppression of superconductivity by an external magnetic field is seen in this more physically accurate picture to be due to the impossibility, in quantum mechanics, of precisely specifying both the centre-of-mass state of a pair and the individual electron kinetic energies. We also discuss the possibility of novel aspects of superconductivity at extremely strong magnetic fields, where recent work has shown that the transition temperature may be enhanced rather than suppressed by a magnetic field and where a quantum treatment is essential.

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