scholarly journals Fluctuation conductivity in two-band superconductor SmFeAsO0.8F0.2

2015 ◽  
Vol 33 (3) ◽  
pp. 644-648 ◽  
Author(s):  
I.N. Askerzade ◽  
R. T. Tagiyeva Askerbeyli
Keyword(s):  
Magnetic Field ◽  
Landau Theory ◽  
Three Dimensional ◽  
Band Model ◽  
Ginzburg Landau ◽  
Band Theory ◽  
Fluctuation Conductivity ◽  
Temperature Dependences ◽  
Two Band Model ◽  
Good Agreement

Abstract In this study we have calculated the fluctuation conductivity near critical temperature of SmFeAsO0.8F0.2 superconductor using two-band Ginzburg-Landau theory. It was illustrated that in the absence of external magnetic field, the two-band model reduced to a single effective band theory with modified temperature dependences. The calculations revealed three-dimensional character of fluctuations of conductivity in the new Fe-based superconductor SmFeAsO0.8F0.2. It has been shown that such a model is in good agreement with experimental data for this compound.

GINZBURG–LANDAU THEORY OF A d-WAVE SUPERCONDUCTOR WITH MASS ANISOTROPY — PAIRING SYMMETRY AND VORTEX STRUCTURES

1996 ◽  
Vol 10 (22) ◽  
pp. 2699-2721 ◽  
Author(s):  
JI-HAI XU ◽  
YONG REN ◽  
C. S. TING
Keyword(s):  
Magnetic Field ◽  
Vortex Lattice ◽  
Landau Theory ◽  
Mass Parameter ◽  
Vortex Structures ◽  
Pairing Symmetry ◽  
Single Vortex ◽  
Ginzburg Landau ◽  
D Wave ◽  
Good Agreement

YBa 2 Cu 3 O 7 (YBCO) exhibits a large anisotropy between the a (or y) and b (or x) axes in the CuO2 planes. This anisotropy can be modeled by introducing an anisotropic mass parameter λ = mx /my. Assuming a d-wave pairing interaction together with a repulsive on-site Coulomb interaction, we developed a Ginzburg–Landau theory for a d-wave superconductor with mass anisotropy in the presence of a magnetic field. We show that the order parameter always has s + d symmetry. The vortex structures for λ = 1 and λ > 1 have been numerically studied. For high T c cuprates with tetragonal structure (λ = 1), the vortex shows a four-fold symmetry and the vortex lattice may have oblique or triangular structure depending on the strength of the applied magnetic field, temperature, and the other parameters. For YBCO we choose λ = 2, the single vortex has an elliptic shape, and the vortex lattice always shows an oblique structure. All these results are in good agreement with experimental measurements.

scholarly journals POINT-CONTACT SPECTROSCOPY OF MAGNESIUM DIBORIDE WITH DIFFERENT COUNTER-ELECTRODES

2003 ◽  
Vol 17 (27n28) ◽  
pp. 1405-1416
Author(s):  
A. I. D'YACHENKO ◽  
V. YU. TARENKOV ◽  
M. A. BELOGOLOVSKII ◽  
V. N. VARYUKHIN ◽  
A. V. ABAL'OSHEV ◽  
...  
Keyword(s):  
Andreev Reflection ◽  
Magnesium Diboride ◽  
Three Dimensional ◽  
Point Contact ◽  
Band Model ◽  
Counter Electrodes ◽  
Break Junctions ◽  
Point Contact Spectroscopy ◽  
Dc Current ◽  
Two Band Model

We report on tunneling and Andreev-reflection conductance spectra of 39 K superconducting magnesium diboride, obtained with Pb and Au counter-electrodes. Two distinct steps at close to 2.7 and 7.1 meV appear in a low-resistance metallic-type Au–MgB 2 junction characteristic, whereas a tunneling-like spectrum measured for the same junction, annealed by the application of DC current, exhibits only a rounded contribution of the larger gap. Junctions with a superconducting lead counter-electrode pressed into a bulk MgB 2 sample reveal two conductance peaks that are interpreted as the result of the formation of a highly-transmitting break junctions inside the magnesium diboride ceramic. Our results strongly support the two-band model with two different gap values on quasi-two-dimensional σ (7.1 meV) and three-dimensional π (2.7 meV) Fermi surface sheets of MgB 2.

scholarly journals Описание колоссального магнитосопротивления La-=SUB=-1.2-=/SUB=-Sr-=SUB=-1.8-=/SUB=-Mn-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=- на основе "спин-поляронного" и "ориентационного" механизмов проводимости в парамагнитной области температур

2020 ◽  
Vol 62 (5) ◽  
pp. 669
Author(s):  
С.А. Гудин ◽  
Н.И. Солин
Keyword(s):  
Magnetic Field ◽  
Colossal Magnetoresistance ◽  
Main Role ◽  
Spin Polaron ◽  
Temperature Range ◽  
Conduction Mechanisms ◽  
Theoretical Investigations ◽  
Temperature Dependences ◽  
The Magnetic Field ◽  
Good Agreement

Experimental and theoretical investigations of the resistance of the La1.2Sr1.8Mn2O7 single crystal in magnetic fields from 0 to 90 kOe and in the temperature range from 75 to 300 K has been studied. The magnetoresistance is determined by the “spin-polaron” and “orientation” conduction mechanisms. Using the method of separating contributions to the magnetoresistance from several conduction mechanisms, the observed magnetoresistance of La1.2Sr1.8Mn2O7 manganite in the temperature range of 75-300 K is described, good agreement between the calculated and experimental data is obtained. In a magnetic field of 0 and 90 kOe, the temperature dependences of the size of the spin polaron (in relative units) are calculated for the temperature range 75–300 K. It is shown, that the КМС value is determined by an increase in the linear size of the spin polaron (along the magnetic field), i.e. the main role in the magnitude of the colossal magnetoresistance is made by the change in the size of the magnetic inhomogeneities of the crystal.

TEMPERATURE DEPENDENCE OF THE CRITICAL CURRENT DENSITY OF SUPERCONDUCTORS IN TWO-BAND GINZBURG–LANDAU THEORY: APPLICATION TO MgB2

2004 ◽  
Vol 18 (13) ◽  
pp. 1931-1936 ◽  
Author(s):  
I. N. ASKERZADE
Keyword(s):  
Critical Current Density ◽  
Temperature Dependence ◽  
Critical Current ◽  
Current Density ◽  
Magnesium Diboride ◽  
Landau Theory ◽  
Ginzburg Landau ◽  
Theory Application ◽  
Gl Theory ◽  
Good Agreement

Temperature dependence of the critical current density j c (T) for the superconducting magnesium diboride MgB 2 is studied in the vicinity of T c by using a two-band Ginzburg–Landau (G–L) theory. The result is in good agreement with experimental data for a bulk MgB 2. Comparision of obtained results with single-band GL theory are presented.

scholarly journals Specific heat jump of two-band superconductor KFe2As2 using Ginzburg-Landau theory

2014 ◽  
Vol 32 (3) ◽  
pp. 465-469 ◽  
Author(s):  
I. Askerzade
Keyword(s):  
Specific Heat ◽  
Order Parameter ◽  
Landau Theory ◽  
Energy Functional ◽  
Order Parameters ◽  
Ginzburg Landau ◽  
Specific Heat Jump ◽  
Nonlinear Temperature Dependence ◽  
Nonlinear Temperature ◽  
Good Agreement

AbstractIn this study specific heat jump using two-gap Ginzburg-Landau (GL) theory has been calculated. In contrast to the previous approaches, we have taken into account intergradient order parameters interaction in the GL free energy functional. The thermodynamic magnetic field revealed nonlinear temperature dependence due to interband interaction between order parameters and their gradients. The calculations showed that the specific heat jump in two-order parameter superconductors was smaller than that of single-order parameter superconductors. It has been shown that such a model is in good agreement with experimental data for KFe2As2 superconductors.

Ginzburg–Landau Theory for Two-Band Isotropic s-Wave Superconductors

2003 ◽  
Vol 17 (16) ◽  
pp. 3001-3020 ◽  
Author(s):  
I. N. Askerzade
Keyword(s):  
Magnetic Field ◽  
Critical Field ◽  
Landau Theory ◽  
Upper Critical Field ◽  
Single Band ◽  
S Wave ◽  
Ginzburg Landau ◽  
Surface Magnetic Field ◽  
Specific Heat Jump ◽  
Gl Theory

Temperature dependence of the upper critical field Hc2(T), lower critical field Hc1(T) and thermodynamic magnetic field Hcm(T) are studied in the vicinity of Tc using a two-band Ginzburg–Landau (GL) theory. The results are shown to be in a good agreement with experimental data for the superconducting magnesium diboride (MgB2) and non-magnetic borocarbides LuNi 2 B 2 C ( YNi 2 B 2 C ). In addition, two-band GL theory was applied for the calculation of specific heat jump, which is smaller than in single-band GL theory. Peculiarities of Little–Parks effect in two-band GL theory are studied also. It is shown that the quantization of the magnetic flux and the relation between surface magnetic field Hc3(T) and upper critical field Hc2(T) are the same as in single band GL theory.

Dynamics of vortex–antivortex creation and annihilation in current-driven mesoscopic superconducting squares

2015 ◽  
Vol 29 (35n36) ◽  
pp. 1550247
Author(s):  
Xiao-Meng Liang ◽  
Guo-Qiao Zha
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Landau Theory ◽  
Symmetric Case ◽  
Time Dependent ◽  
Dynamical Process ◽  
Applied Bias ◽  
Ginzburg Landau ◽  
Dc Drive ◽  
Vortex Velocity

In this paper, based on the time-dependent Ginzburg–Landau theory, we study the dynamics of vortex–antivortex (V–Av) pairs in a mesoscopic superconducting square with a small hole under applied bias currents. For the sample with a centered hole, a V–Av pair can nucleate at the hole edges and moves in opposite directions perpendicular to applied constant DC drive. The influence of the external magnetic field on the (anti)vortex velocity and the lifetime of V–Av pairs is mainly investigated. Different modes in the dynamical process of the V–Av collision and annihilation are identified. Moreover, in the case when the hole is displaced from the center of the square, the V–Av dynamics behaves quite differently from the symmetric case due to the shift of the V–Av creation point.

scholarly journals Persistence of superconductivity in thin shells beyond Hc1

2016 ◽  
Vol 18 (04) ◽  
pp. 1550047 ◽  
Author(s):  
Andres Contreras ◽  
Xavier Lamy
Keyword(s):  
Magnetic Field ◽  
Model Problem ◽  
Landau Theory ◽  
Normal Component ◽  
Mean Field ◽  
Compact Surface ◽  
Thin Shells ◽  
Symmetric Model ◽  
Ginzburg Landau ◽  
Zero Locus

In Ginzburg–Landau theory, a strong magnetic field is responsible for the breakdown of superconductivity. This work is concerned with the identification of the region where superconductivity persists, in a thin shell superconductor modeled by a compact surface [Formula: see text], as the intensity [Formula: see text] of the external magnetic field is raised above [Formula: see text]. Using a mean field reduction approach devised by Sandier and Serfaty as the Ginzburg–Landau parameter [Formula: see text] goes to infinity, we are led to studying a two-sided obstacle problem. We show that superconductivity survives in a neighborhood of size [Formula: see text] of the zero locus of the normal component [Formula: see text] of the field. We also describe intermediate regimes, focusing first on a symmetric model problem. In the general case, we prove that a striking phenomenon we call freezing of the boundary takes place: one component of the superconductivity region is insensitive to small changes in the field.

scholarly journals Reliability of the Ginzburg–Landau Theory in the BCS-BEC Crossover by Including Gaussian Fluctuations for 3D Attractive Fermions

2021 ◽  
Vol 6 (4) ◽  
pp. 49
Author(s):  
Filippo Pascucci ◽  
Andrea Perali ◽  
Luca Salasnich
Keyword(s):  
Landau Theory ◽  
Landau Equation ◽  
Three Dimensional ◽  
Einstein Condensate ◽  
Unitary Limit ◽  
Ginzburg Landau ◽  
Gaussian Fluctuations ◽  
Bose Einstein Condensate ◽  
Bose Einstein ◽  
Physical Quantities

We calculate the parameters of the Ginzburg–Landau (GL) equation of a three-dimensional attractive Fermi gas around the superfluid critical temperature. We compare different levels of approximation throughout the Bardeen–Cooper–Schrieffer (BCS) to the Bose–Einstein Condensate (BEC) regime. We show that the inclusion of Gaussian fluctuations strongly modifies the values of the Ginzburg–Landau parameters approaching the BEC regime of the crossover. We investigate the reliability of the Ginzburg–Landau theory, with fluctuations, studying the behavior of the coherence length and of the critical rotational frequencies throughout the BCS-BEC crossover. The effect of the Gaussian fluctuations gives qualitative correct trends of the considered physical quantities from the BCS regime up to the unitary limit of the BCS-BEC crossover. Approaching the BEC regime, the Ginzburg–Landau equation with the inclusion of Gaussian fluctuations turns out to be unreliable.

Sign in / Sign up

Export Citation Format

Share Document