DETERMINATIONS OF UPPER CRITICAL FIELDS IN CONTINUOUS GINZBURG–LANDAU MODEL

2004 ◽  
Vol 15 (06) ◽  
pp. 783-807
Author(s):  
L. WANG ◽  
H. S. LIM ◽  
C. K. ONG
Keyword(s):  
Critical Field ◽  
Eigenvalue Problems ◽  
Upper Critical Field ◽  
Critical Fields ◽  
Ginzburg Landau ◽  
Direction Parallel ◽  
Landau Model ◽  
The Magnetic Field ◽  
Good Agreement

Novel procedures to determine the parallel upper critical field Bc2 (one-dimensional, 1D) have been proposed within a continuous Ginzburg–Landau model. Unlike conventional methods, where Bc2 is obtained through the determination of the smallest eigenvalue of an appropriate eigen equation, the square of the magnetic field is treated as eigenvalue problems by two procedures so that the upper critical field can be directly deduced. The two procedures proposed are extended to determine the upper critical field in the c–a crystal plane (two-dimensional, 2D) with an arbitrary angle θ tilted from the c-axis. The calculated Bc2 from the two procedures are consistent with each other in both 1D and 2D cases. Moreover, the values of Bc2 near the direction parallel to the layers obtained in the 2D case well approximate the counterparts in the 1D case. The properties of the calculated Bc2 are in reasonably good agreement with existing theories and experiments. The profiles of the order parameters associated with Bc2 for both 1D and 2D cases are Gaussian-like, further validating the methodology proposed.

Ginzburg–Landau theory of the Abrikosov vortex state near the upper critical field

1982 ◽  
Vol 60 (3) ◽  
pp. 299-303 ◽  
Author(s):  
A. E. Jacobs
Keyword(s):  
Critical Field ◽  
Landau Theory ◽  
Upper Critical Field ◽  
Vortex State ◽  
Quantization Condition ◽  
Abrikosov Vortex ◽  
Ginzburg Landau ◽  
Type Ii Superconductors ◽  
Flux Quantization ◽  
The Magnetic Field

A method which preserves the flux-quantization condition in all orders of perturbation theory is applied to the Ginzburg–Landau theory of type-II superconductors near the upper critical field. Expansions are obtained for the order parameter, the magnetic field, and the free energy; previous results are verified and extended to one higher order in Hc2 – Ha.

ON THE SECOND CRITICAL FIELD FOR A GINZBURG–LANDAU MODEL WITH FERROMAGNETIC INTERACTIONS

2004 ◽  
Vol 16 (02) ◽  
pp. 147-174 ◽  
Author(s):  
STAN ALAMA ◽  
LIA BRONSARD
Keyword(s):  
Magnetic Field ◽  
Critical Field ◽  
Order Parameter ◽  
Upper Critical Field ◽  
Average Energy ◽  
Spin Coupling ◽  
P Wave ◽  
Ginzburg Landau ◽  
Landau Model ◽  
Second Critical Field

We consider a two-dimensional Ginzburg–Landau model for superconductors which exhibit ferromagnetic ordering in the superconducting phase, introduced by physicists to describe unconventional p-wave superconductors. In this model the magnetic field is directly coupled to a vector-valued order parameter in the energy functional. We show that one effect of spin coupling is to increase the second critical field Hc2, the value of the applied magnetic field at which superconductivity is lost in the bulk. Indeed, when the spin coupling is strong we show that the upper critical field is no longer present, confirming predictions in the physics literature. We treat the energy density as a measure, and show that the order parameter converges (as the Ginzburg–Landau parameter κ→∞) in an average sense to a constant determined by the average energy.

Critical Field Measurements on Superconducting Graphite-KHG Multilayers

1987 ◽  
Vol 103 ◽  
Author(s):  
A. Chaiken ◽  
P. M. Tedrow ◽  
G. Dresselhaus
Keyword(s):  
Critical Field ◽  
Qualitative Agreement ◽  
Field Measurements ◽  
Critical Fields ◽  
Ginzburg Landau ◽  
Landau Model ◽  
Anisotropic Superconductivity ◽  
Upper Critical Fields

ABSTRACTUpper critical fields of graphite-KHg multilayers with 10Å periodicity were measured as a function of angle and temperature. The Hc2 (θ, T) data were compared to the anisotropic Ginzburg-Landau model and were found to be in qualitative agreement, except at the lowest reduced temperatures, where significant deviations are found. The primary deviations from the anisotropic GL model are first, that the values of the critical field at the lowest temperatures are found to be higher than that predicted by the model, and secondly, the critical field anistropy ratio is found to be temperaturedependent. These deviations are discussed in light of more detailed models of anisotropic superconductivity.

ANGULAR DEPENDENCE OF UPPER CRITICAL FIELD FOR THE TWO-BAND SUPERCONDUCTOR Lu2Fe3Si5

2010 ◽  
Vol 24 (12) ◽  
pp. 1185-1190 ◽  
Author(s):  
MINXIA LIU ◽  
HAI HUANG
Keyword(s):  
Experimental Data ◽  
Angular Dependence ◽  
Critical Field ◽  
Landau Theory ◽  
Upper Critical Field ◽  
Ginzburg Landau ◽  
Theoretical Results ◽  
Good Agreement

Based on the two-band Ginzburg–Landau theory, we study the angular dependence of the upper critical field for the superconducting crystal Lu 2 Fe 3 Si 5. When θ=0 and θ=π/2, the theoretical results are in good agreement with the experimental data. Hence, the results support the existence of two-gap superconductivity in Lu 2 Fe 3 Si 5, previously suggested from experiments.

scholarly journals Multiband effects on the upper critical field angular dependence of 122-family iron pnictide superconductors

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
I. F. Llovo ◽  
C. Carballeira ◽  
D. Sóñora ◽  
A. Pereiro ◽  
J. J. Ponte ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Angular Dependence ◽  
Critical Field ◽  
Upper Critical Field ◽  
Single Band ◽  
Band Model ◽  
Cooper Pairs ◽  
Ginzburg Landau ◽  
Superconducting Fluctuations

AbstractDetailed measurements of the in-plane resistivity were performed in a high-quality Ba($$\hbox {Fe}_{1-x}\hbox {Co}_{{x}}$$ Fe 1 - x Co x )$$_2\hbox {As}_2$$ 2 As 2 ($$x=0.065$$ x = 0.065 ) single crystal, in magnetic fields up to 9 T and with different orientations $$\theta$$ θ relative to the crystal c axis. A significant $$\rho (T)_{H,\theta }$$ ρ ( T ) H , θ rounding is observed just above the superconducting critical temperature $$T_c$$ T c due to Cooper pairs created by superconducting fluctuations. These data are analyzed in terms of a generalization of the Aslamazov-Larkin approach, that extends its applicability to high reduced-temperatures and magnetic fields. This method allows us to carry out a criterion-independent determination of the angular dependence of the upper critical field, $$H_{c2}(\theta )$$ H c 2 ( θ ) . In spite of the relatively small anisotropy of this compound, it is found that $$H_{c2}(\theta )$$ H c 2 ( θ ) presents a significant deviation from the single-band 3D anisotropic Ginzburg-Landau (3D-aGL) approach, particularly for large $$\theta$$ θ (typically above $$\sim 60^o$$ ∼ 60 o ). These results are interpreted in terms of the multiband nature of these materials, in contrast with other proposals for similar $$H_{c2}(\theta )$$ H c 2 ( θ ) anomalies. Our results are also consistent with an effective anisotropy factor almost temperature independent near $$T_c$$ T c , a result that differs from the ones obtained by using a single-band model.

Vortex Lattice Structure of High Temperature Superconductors

2003 ◽  
Vol 17 (18n20) ◽  
pp. 3415-3422
Author(s):  
Shi-Ping Zhou ◽  
Hao-Chen Du ◽  
Hong-Yin Liao
Keyword(s):  
High Temperature ◽  
Transition Temperature ◽  
Critical Field ◽  
Vortex Lattice ◽  
Lattice Structure ◽  
High Temperature Superconductors ◽  
Upper Critical Field ◽  
Ginzburg Landau ◽  
Landau Model ◽  
Upward Curvature

We study vortex lattice structure of high temperature superconductors by using the Ginzburg–Landau model. The structure of the vortex lattice is oblique at the temperatures well below the transition temperature Tc, where the mixed s–d state is expected to have the lowest energy. Whereas, very close to Tc, the dx2-y2 wave is slightly lower in energy, and a triangular vortex lattice recovers. The coexistence and the coupling between the s- and d-waves account for the upward curvature of the upper critical field curve HC2(T).

CRITICAL FIELD AND MAGNETORESISTANCE OF SINGLE CRYSTAL TmNi2B2C

1999 ◽  
Vol 13 (29n31) ◽  
pp. 3715-3717 ◽  
Author(s):  
D. G. NAUGLE ◽  
K. D. D. RATHNAYAKA ◽  
K. CLARK ◽  
P. C. CANFIELD
Keyword(s):  
Magnetic Field ◽  
Transition Temperature ◽  
Single Crystal ◽  
Critical Field ◽  
Superconducting Transition Temperature ◽  
Magnetic Transition ◽  
Upper Critical Field ◽  
Superconducting Transition ◽  
Large Anisotropy ◽  
The Magnetic Field

In-plane resistance as a function of magnitude and direction of the magnetic field and the temperature has been measured for TmNi2B2C from above the superconducting transition temperature at 10.7 K to below the magnetic transition TN=1.5 K. The superconducting upper critical field HC2(T) exhibits a large anisotropy and structure in the vicinity of TN. The magnetoresistance above TC is large and changes sign as the direction of the magnetic field is rotated from in-plane to parallel with the c-axis.

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