First-principles calculation of the superconducting gap function due to electron-electron interaction for YBa/sub 2/Cu/sub 3/O/sub 7-//sub x/

Journal Article · Wed Feb 01 00:00:00 EST 1989 · Phys. Rev. B: Condens. Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.39.2217· OSTI ID:6757635

Chui, S T; Kasowski, R V; Hsu, W Y

We argue that because of the anisotropic nature of YBa/sub 2/Cu/sub 3/O/sub 7-//sub x/, one-dimensional-type charge- and spin-density fluctuations produce an effective attraction that overcomes the electron-electron Coulomb repulsion, but only at large distances. This effective attraction is further enhanced by band-structure effects such that a substantial superconducting transition temperature can be obtained. Without making any assumption of the symmetry of the gap function, we solve the Bardeen-Cooper-Schrieffer (BCS) superconducting gap equation for the six bands closest to the Fermi level. A highly anisotropic gap function with a maximum of about 0.11 eV is found. From the linearized gap equation, a transition temperature of about 0.035 eV is obtained. This is about one-quarter the maximum of the gap function, consistent with the experimental ratio of the transition temperature to the gap determined from tunneling, infrared, and nuclear quadrupole resonance measurements. The important participants to the superconducting pair come from electrons close to planar copper (Cu(2)) and chain oxygen (O(1) and O(4)) sites, consistent with recent quadrupole resonance measurements. Our calculation produces a coherence length of the order of 30 A in the xy direction, the same order of magnitude as the experimental result and considerably smaller than the conventional magnitude of ordinary BCS materials. Similar calculations for YBa/sub 2/Cu/sub 3/O/sub 6.5/ where periodic O vacancies are introduced along the one-dimensional Cu-O chains shows that the transition temperature is reduced by half.

• Research Organization: Bartol Research Institute, University of Delaware, Newark, Delaware 19716
• OSTI ID: 6757635
• Journal Information: Phys. Rev. B: Condens. Matter; (United States), Vol. 39:4
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BARIUM OXIDES
ELECTRON-ELECTRON COUPLING
SUPERCONDUCTIVITY
COPPER OXIDES
YTTRIUM OXIDES
ANISOTROPY
BCS THEORY
ENERGY GAP
FERMI LEVEL
INFRARED RADIATION
NUCLEAR QUADRUPOLE RESONANCE
SPIN WAVES
TRANSITION TEMPERATURE
WAVE FUNCTIONS
ALKALINE EARTH METAL COMPOUNDS
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CHALCOGENIDES
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ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELECTROMAGNETIC RADIATION
ENERGY LEVELS
FUNCTIONS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
RADIATIONS
RESONANCE
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
YTTRIUM COMPOUNDS
360204* - Ceramics
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656100 - Condensed Matter Physics- Superconductivity