On intrinsic and extrinsic effects in the surface impedance of cuprate superconductors

1992 ◽  
Vol 5 (4) ◽  
pp. 331-337 ◽  
Author(s):  
J. Halbritter
Keyword(s):  
Surface Impedance ◽  
Cuprate Superconductors ◽  
Extrinsic Effects

Surface impedance measurements of cuprate superconductors: Nd1.85.85Ce0.15CuO4?? ?A case study

1994 ◽  
Vol 7 (2) ◽  
pp. 453-458 ◽  
Author(s):  
Steven M. Anlage ◽  
Dong -Ho Wu ◽  
Jian Mao ◽  
Sining Mao ◽  
X. X. Xi ◽  
...  
Keyword(s):  
Surface Impedance ◽  
Cuprate Superconductors ◽  
Impedance Measurements

On Extrinsic Effects in the Surface Impedance of Cuprate Superconductors

1992 ◽  
Vol 275 ◽  
Author(s):  
J. Halbritter
Keyword(s):  
Field Dependence ◽  
Surface Impedance ◽  
Cuprate Superconductors ◽  
Nonlinear Effects ◽  
Weighting Factor ◽  
Weak Links ◽  
Flux Flow ◽  
Unique Method ◽  
Rf Devices ◽  
Thin Seam

ABSTRACTPresently, the rf surface impedance Z of cuprate superconductors is still shrinking with material improvements, which is shown clearly by Z = Z1+Zres still dominated by extrinsic properties summarized in Zres. We present evidence that Zres is due to the large leakage current jbi and the small critical current jcj of weak links. The latter destroys the intrinsic shielding from a λ1 -thin seam λJ deep into the bulk. This causes rf residual losses Rres ≈ (ΩμO)2λJ3 σb1/2. Rres stays finite at T≃O by σb1(T→O)≈σb1(αjb1) being amplified by (λj/λ1>103 as a weighting factor. An appropriate measure of weak links is the grain boundary resistance Rbn(∝ρ(O)) enhancing λj ∝ Rbn and Rres ∝ Rbn2. Thus, Zres is minimal for minimal extrapolated normal conducting resistivity ρ(T→O).To identify the weak links as new entity the H-field dependence is most helpful, because at very low fields Hc1J∝ 1/λJ Josephson fluxons penetrate into the weak links. These Josephson fluxons show negligible flux flow or flux creep, and enhance Zres by λJ(H, T) ∝ l/√Jjc (H, T). The measured JcJ (H, T) - and Jbl - values explain Zres quantitatively as well as in temperature ∝ ( a+ Tn) (n ≈ 1, T<Tc/2) and in field ∝ (b + Hn) (n≈1, H>Hc1J) dependence being thus a unique method to obtain the different Hc1-values. The strength of the field dependence d Zres/dH ∝ Zres (Hc1J*)/Hc2J(T) is not only a measure of Zres and HC2j(T) but is crucial for nonlinear effects and (fluxon) noise also, which limits the performance of rf devices.

Quantitative structure determination of interfaces through Z-contrast imaging and electron energy loss spectroscopy

1996 ◽  
Vol 54 ◽  
pp. 104-105
Author(s):  
S. J. Pennycook ◽  
P. D. Nellist ◽  
N. D. Browning ◽  
P. A. Langjahr ◽  
M. Rühle
Keyword(s):  
Grain Boundaries ◽  
Cuprate Superconductors ◽  
Structure Refinement ◽  
3D Structure ◽  
Real Space ◽  
Contrast Imaging ◽  
Coordination Polyhedra ◽  
Burgers Vector ◽  
Z Contrast ◽  
Contrast Image

The simultaneous use of Z-contrast imaging with parallel detection EELS in the STEM provides a powerful means for determining the atomic structure of grain boundaries. The incoherent Z-contrast image of the high atomic number columns can be directly inverted to their real space arrangement, without the use of preconceived structure models. Positions and intensities may be accurately quantified through a maximum entropy analysis. Light elements that are not visible in the Z-contrast image can be studied through EELS; their coordination polyhedra determined from the spectral fine structure. It even appears feasible to contemplate 3D structure refinement through multiple scattering calculations.The power of this approach is illustrated by the recent study of a series of SrTiC>3 bicrystals, which has provided significant insight into some of the basic issues of grain boundaries in ceramics. Figure 1 shows the structural units deduced from a set of 24°, 36° and 65° symmetric boundaries, and 24° and 45° asymmetric boundaries. It can be seen that apart from unit cells and fragments from the perfect crystal, only three units are needed to construct any arbitrary tilt boundary. For symmetric boundaries, only two units are required, each having the same Burgers, vector of a<100>. Both units are pentagons, on either the Sr or Ti sublattice, and both contain two columns of the other sublattice, imaging in positions too close for the atoms in each column to be coplanar. Each column was therefore assumed to be half full, with the pair forming a single zig-zag column. For asymmetric boundaries, crystal geometry requires two types of dislocations; the additional unit was found to have a Burgers’ vector of a<110>. Such a unit is a larger source of strain, and is especially important to the transport characteristics of cuprate superconductors. These zig-zag columns avoid the problem of like-ion repulsion; they have also been seen in TiO2 and YBa2Cu3O7-x and may be a general feature of ionic materials.

CRITICAL STATE MODEL FOR CUPRATE SUPERCONDUCTORS

1988 ◽  
Vol 49 (C8) ◽  
pp. C8-2231-C8-2232
Author(s):  
A. M. Portis ◽  
M. Stalder ◽  
G. Stefanicki ◽  
F. Waldner ◽  
M. Warden
Keyword(s):  
Critical State ◽  
Cuprate Superconductors ◽  
Critical State Model ◽  
State Model

PONDEROMOTIVE EFFECT OF ELECTROMAGNETIC WAVES ON THIN VIBRATORS WITH WEAKLY PERTURBED SURFACE IMPEDANCE

2020 ◽  
Vol 79 (14) ◽  
pp. 1205-1215
Author(s):  
Yu. M. Penkin ◽  
V. A. Katrich ◽  
M. V. Nesterenko ◽  
S. L. Berdnik
Keyword(s):  
Surface Impedance ◽  
Electromagnetic Waves
Sign in / Sign up

Export Citation Format

Share Document