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.

ZERO FIELD EXCESS CONDUCTIVITY STUDIES IN THE Bi-Sr-Ca-Cu-O SYSTEM

1992 ◽  
Vol 06 (29) ◽  
pp. 1857-1865 ◽  
Author(s):  
S. RAVI ◽  
V. SESHU BAI
Keyword(s):  
Mean Field ◽  
Excess Conductivity ◽  
Zero Field ◽  
Pair Breaking ◽  
Field Region ◽  
Average Value ◽  
Two Samples ◽  
The Mean ◽  
Breaking Time

The excess conductivity (∆σ) data on several samples of 85 K phase and 110 K phase of Bi-Sr-Ca-Cu-O system were fitted to a sum of direct (AL) and indirect (MT) contribution of fluctuation induced excess conductivity, in the mean field region. The samples of the 85 K phase are of compositions Bi2Sr2CaCu2Oy, Bi2Sr2CaCu2Ag0.8Oy, and Bi2Sr2.14Ca0.86Cu2Oy with Tc (zero) of 78.9 K, 86.5 K and 81.8 K respectively. The two samples of 110 K phase with composition Bi1.2Pb0.3Sr1.5Ca2Cu3Oy were prepared from nitrate and citrate routes respectively and have Tc (zero) of 105.3 K and 102.9 K. We find from our analysis relatively strong pair-breaking effects in both 85 K and 110 K phases, indicating the contribution of Maki-Thompson term to the excess conductivity to be rather insignificant. The average value estimated for the phase-breaking time for the 85 K and 110 K phases are (3.7±0.5)×10−16s and(11.3±1.6)×10−16s respectively, at 100 K.

scholarly journals Two-term expansion of the ground state one-body density matrix of a mean-field Bose gas

2021 ◽  
Vol 60 (3) ◽  
Author(s):  
Phan Thành Nam ◽  
Marcin Napiórkowski
Keyword(s):  
Density Matrix ◽  
Ground State ◽  
Mean Field ◽  
Interaction Strength ◽  
Bose Gas ◽  
Body Density ◽  
The Mean ◽  
The One ◽  
Mean Field Regime ◽  
Number Of Particles

AbstractWe consider the homogeneous Bose gas on a unit torus in the mean-field regime when the interaction strength is proportional to the inverse of the particle number. In the limit when the number of particles becomes large, we derive a two-term expansion of the one-body density matrix of the ground state. The proof is based on a cubic correction to Bogoliubov’s approximation of the ground state energy and the ground state.

Modification of charge density wave fluctuations by charge perturbations

2002 ◽  
Vol 12 (9) ◽  
pp. 77-78
Author(s):  
S. N. Artemenko
Keyword(s):  
Electric Field ◽  
Linear Response ◽  
Chemical Potential ◽  
Density Wave ◽  
Mean Field ◽  
Phase Fluctuations ◽  
Fluctuation Dissipation ◽  
Fluctuation Dissipation Theorem ◽  
The Mean ◽  
Field Transition

Spectral density of fluctuations of the CDW phase are calculated taking into account electric field induced by phase fluctuations. The approach based upon the fluctuation-dissipation theorem (FDT) combined with equations of linear response of the CDW conductor is used. Fluctuating electric field is found to suppress fluctuations of the phase, while fluctuations of the electric potential are sizeable. This suggests that transition from the CDW to the normal state (which is usually observed well below the mean-field transition temperature) may he provoked by fluctuations of the chemical potential, rather than by destruction of the CDW coherence between conducting chains due to phase fluctuations.

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.

FLUCTUATION CONDUCTIVITY EFFECTS ON THERMOELECTRIC POWER OF GRANULAR Bi1.75Pb0.25Ca2Sr2Cu3O10 SUPERCONDUCTOR

1989 ◽  
Vol 03 (03) ◽  
pp. 241-248 ◽  
Author(s):  
CH. LAURENT ◽  
S.K. PATAPIS ◽  
S.M. GREEN ◽  
H.L. LUO ◽  
C. POLITIS ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
High Temperature ◽  
Thermoelectric Power ◽  
High Temperature Superconductivity ◽  
Mean Field ◽  
Temperature Derivative ◽  
Fluctuation Conductivity ◽  
Straight Line ◽  
The Mean ◽  
Mean Field Regime

We report precise measurements of the thermoelectric power (TEP) of granular superconducting Bi 1.75 Pb 0.25 Ca 2 Sr 2 Cu 3 O 10. The TEP is strictly linear at high temperature. Superconductivity fluctuations set in at about 140 K. From the temperature derivative of the excess TEP (with respect to a straight line at “high temperature”), the critical behavior is obtained in the mean field regime, and is found identical to that of the temperature derivative of the excess electrical resistivity.

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.

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