Theory of upper critical field, fluctuation conductivity, and fluctuation specific heat for high-Tcsuperconductors in a magnetic field

1989 ◽  
Vol 39 (1) ◽  
pp. 278-286 ◽  
Author(s):  
C. T. Rieck ◽  
Th. Wölkhausen ◽  
D. Fay ◽  
L. Tewordt
Keyword(s):  
Magnetic Field ◽  
Specific Heat ◽  
Critical Field ◽  
Upper Critical Field ◽  
Field Fluctuation ◽  
Fluctuation Conductivity

Upper critical field, fluctuation conductivity, and dimensionality ofYBa2Cu3O7−x

1988 ◽  
Vol 37 (13) ◽  
pp. 7861-7864 ◽  
Author(s):  
B. Oh ◽  
K. Char ◽  
A. D. Kent ◽  
M. Naito ◽  
M. R. Beasley ◽  
...  
Keyword(s):  
Critical Field ◽  
Upper Critical Field ◽  
Field Fluctuation ◽  
Fluctuation Conductivity

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.

UPPER CRITICAL FIELD OF UNCONVENTIONAL SUPERCONDUCTORS FROM CHEMICAL EQUILIBRIUM

1999 ◽  
Vol 13 (29n31) ◽  
pp. 3443-3448 ◽  
Author(s):  
A. KALLIO ◽  
J. HISSA ◽  
T. HÄYRYNEN ◽  
V. BRÄYSY
Keyword(s):  
Magnetic Field ◽  
Critical Field ◽  
Normal State ◽  
Chemical Equilibrium ◽  
Critical Density ◽  
Upper Critical Field ◽  
Universal Function ◽  
Zero Magnetic Field ◽  
Mathematical Treatment ◽  
Critical Fields

We have shown previously that many normal state properties of high Tc superconductors in zero magnetic field can be understood in terms of a single universal function f(t) in the scaled variable t=T/T*, where T* is connected with temperature independent gap 2Δ=2kBT*, which gives the binding energy of a pair in analogy with dissociation of molecules. The function f(t) determines the fraction of bosons (B++) and fermions (h+) at temperature T and it is obtained from the mathematical treatment of chemical equilibrium with respect to the reaction B++⇌ 2h+. Since for magnetic fields of reasonable strength the Zeeman energy is much smaller than the pseudo gap Δ~100K-800K, the function f(t) in the normal state is largely independent of magnetic field. The main effect of the magnetic field is to increase the tendency for bosons to localize. This means that the critical density nL for delocalization in the ab-plane direction and the critical density for superfluidity nc (≳ nL) both increase with magnetic field. This causes the corresponding temperatures TBL(H) and Tc(H) to go down with the field. Assuming a power law dependence nc(H)/nc(0)=1+AHμ, the upper critical fields for several heavy fermion compounds are shown to fall into a single curve. The purpose here is to show that the upper critical field Hc2(y) (y=Tc(H)/Tc(0)) can be expressed in a simple way in terms of f(t). We show that this theory predicts all the shapes of Hc2(y) observed in several unconventinal superconductors such as Tl 2 Ba 2 CuO 6+δ, with Tc=15 K.

Upper critical field and fluctuation conductivity in Nb-doped strontium titanate thin films

2000 ◽  
Vol 62 (2) ◽  
pp. 1408-1413 ◽  
Author(s):  
Arnold Leitner ◽  
David Olaya ◽  
Charles T. Rogers ◽  
John C. Price
Keyword(s):  
Thin Films ◽  
Strontium Titanate ◽  
Critical Field ◽  
Upper Critical Field ◽  
Fluctuation Conductivity
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