ANOMALOUS FERMIONIC OCCUPANCY FOR HIGH-Tc SUPERCONDUCTING LAYERED MATERIALS

1992 ◽  
Vol 06 (15) ◽  
pp. 935-942 ◽  
Author(s):  
G. CARMONA ◽  
R. M. MÉNDEZ-MORENO ◽  
S. OROZCO ◽  
M. A. ORTÍZ ◽  
M. MORENO ◽  
...  
Keyword(s):  
Copper Oxide ◽  
Cuprate Superconductors ◽  
Good Description ◽  
Layered Materials ◽  
High Tc ◽  
Infinite Slab ◽  
Fermion Pairs

Tighter-bound Cooper fermion pairs are obtained in a model with anomalous occupancy for fermions confined to an infinite slab mimicking the copper-oxide planes in cuprate superconductors. The model is applied to several typical high T c superconductors. T c values in this model are higher than those obtained with normal occupancy. Small but nonzero values for the anomalous occupancy parameter give a remarkably good description of the data.

MINIMAL ANOMALOUS OCCUPANCY IN HIGH-Tc SUPERCONDUCTIVITY

1993 ◽  
Vol 07 (24n25) ◽  
pp. 1601-1609 ◽  
Author(s):  
R.M. MÉNDEZ-MORENO ◽  
M. MORENO ◽  
S. OROZCO ◽  
M.A. ORTÍZ
Keyword(s):  
Critical Temperature ◽  
Copper Oxide ◽  
Cuprate Superconductors ◽  
Normal Limit ◽  
Good Description ◽  
Energy Scale ◽  
Oxide Superconductors ◽  
High Tc ◽  
Copper Oxide Superconductors ◽  
Fermion Gas

A study of a minimal anomalous occupancy is carried out when a small gap occurs near the Fermi surface. A limit which tends softly to the normal occupancy can be introduced. This framework is applied to a quasi-bidimensional fermion gas which can mimick the copper oxide planes in cuprate superconductors. The energy scale implied by this minimally anomalous occupancy (the soft normal limit) for high-T c cuprate superconductors is of the order of the Debye energy. Yet this anomalous occupancy framework overcomes the phonon barrier and a good description for the critical temperature of a representative set of high-T c copper oxide superconductors is obtained.

High Resolution Electron Microscopy of internal interfaces in layered materials

1990 ◽  
Vol 48 (4) ◽  
pp. 320-321
Author(s):  
Yoichi Ishida ◽  
Hideki Ichinose ◽  
Yutaka Takahashi ◽  
Jin-yeh Wang
Keyword(s):  
Grain Boundaries ◽  
Mirror Symmetry ◽  
Functional Materials ◽  
High Resolution Electron Microscopy ◽  
Layered Materials ◽  
Plane Boundary ◽  
Chemical Information ◽  
Layer Plane ◽  
High Tc ◽  
Cubic Metals

Layered materials draw attention in recent years in response to the world-wide drive to discover new functional materials. High-Tc superconducting oxide is one example. Internal interfaces in such layered materials differ significantly from those of cubic metals. They are often parallel to the layer of the neighboring crystals in sintered samples(layer plane boundary), while periodically ordered interfaces with the two neighboring crystals in mirror symmetry to each other are relatively rare. Consequently, the atomistic features of the interface differ significantly from those of cubic metals. In this paper grain boundaries in sintered high-Tc superconducting oxides, joined interfaces between engineering ceramics with metals, and polytype interfaces in vapor-deposited bicrystal are examined to collect atomic information of the interfaces in layered materials. The analysis proved that they are not neccessarily more complicated than that of simple grain boundaries in cubic metals. The interfaces are majorly layer plane type which is parallel to the compound layer. Secondly, chemical information is often available, which helps the interpretation of the interface atomic structure.

ENERGY BAND OVERLAPPING IN HIGH-Tc SUPERCONDUCTORS

1996 ◽  
Vol 10 (30) ◽  
pp. 1483-1490 ◽  
Author(s):  
M. MORENO ◽  
R. M. MÉNDEZ-MORENO ◽  
M. A. ORTIZ ◽  
S. OROZCO
Keyword(s):  
Weak Coupling ◽  
Cuprate Superconductors ◽  
Weak Coupling Limit ◽  
Band Model ◽  
Coupling Constant ◽  
High Tc Superconductors ◽  
Energy Bands ◽  
Effective Coupling ◽  
High Tc ◽  
Two Band Model

Multi-band superconductors are analyzed and the relevance of overlapping energy bands to the high-T c of these materials is studied. Within the BCS framework, a two band model with generalized Fermi surface topologies is developed. Values of the overlapped occupancy parameters for typical cuprate superconductors are obtained as a function of the ratio R and the effective coupling constant, λ, in the weak-coupling limit. The overlap scale is of the order or lower than the cutoff (Debye) energy. The typical behavior of the isotope effect is obtained. As these superconductors have transition temperatures above the phonon barrier, the results of this approach are important to the generic understanding of the high-T c superconducting mechanism.

scholarly journals EFFECTS OF c-AXIS HOPPING IN THE INTERLAYER TUNNELING MODEL OF HIGH-Tc LAYERED CUPRATES

1999 ◽  
Vol 13 (13) ◽  
pp. 1619-1632
Author(s):  
BIPLAB CHATTOPADHYAY ◽  
A. N. DAS
Keyword(s):  
Experimental Data ◽  
Transition Temperature ◽  
Cuprate Superconductors ◽  
Interlayer Coupling ◽  
Superconducting Gap ◽  
Tunneling Model ◽  
High Tc ◽  
Optimal Doping ◽  
Pair Tunneling ◽  
Layered Cuprates

We consider the interlayer pair-tunneling model for layered cuprates, including an effective single particle hopping along the c-axis. A phenomenological suppression of the c-axis hopping matrix element, by the pseudogap in cuprate superconductors, is incorporated. At optimal doping, quantities characteristic to the superconducting state, such as the transition temperature and the superconducting gap are calculated. Results from our calculations are consistent with the experimental observations with the noteworthy point that, the superconducting gap as a function of temperature shows excellent match to the experimental data. Predictions within the model, regarding T c variation with interlayer coupling, are natural outcomes which could be tested further.

Optical studies on the high Tc cuprate superconductors

1991 ◽  
Vol 43 (3) ◽  
pp. 4075
Author(s):  
Jiro Tanaka ◽  
Masaaki Shimizu ◽  
Koji Kamiya ◽  
Satoru Miyamoto ◽  
Yukio Tanaka
Keyword(s):  
Cuprate Superconductors ◽  
Optical Studies ◽  
High Tc

scholarly journals Flux Penetration Effects in High-Tc SQUIDs

1989 ◽  
Vol 42 (4) ◽  
pp. 401
Author(s):  
GJ SIoggett ◽  
lK Harvey ◽  
L Wieczorek ◽  
RE Binks ◽  
R Driver
Keyword(s):  
Magnetic Field ◽  
Copper Oxide ◽  
Direct Measurement ◽  
Barium Copper Oxide ◽  
Break Junction ◽  
Flux Penetration ◽  
High Tc ◽  
Bulk Ybco ◽  
Barium Copper ◽  
Yttrium Barium

Two experiments pertaining to the effects of intergranular flux penetration in high-Tc yttrium-barium-copper oxide (YBCO) SQUIDs are described. The first is a direct measurement of the flux noise of bulk YBCO exposed to the earth's magnetic field, and the second involves the fabrication and testing of break junction d.c. SQUIDs. Implications of a number of undesirable effects seen in these experiments are discussed.

ChemInform Abstract: NMR and NQR Studies in High-Tc Oxides: Yttrium Barium Copper Oxide, YBa2Cu3Oy (y = 6.0-6.91)

ChemInform ◽  
1990 ◽  
Vol 21 (3) ◽  
Author(s):  
H. YASUOKA ◽  
T. SHIMIZU ◽  
T. IMAI ◽  
S. SASAKI ◽  
Y. UEDA ◽  
...  
Keyword(s):  
Yttrium Barium Copper Oxide ◽  
Copper Oxide ◽  
Barium Copper Oxide ◽  
High Tc ◽  
Barium Copper ◽  
Yttrium Barium
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