d sup 9 spin-polaron theory of high- T sub c superconductivity

Journal Article · Sun Mar 01 04:00:00 EST 1992 · Physical Review, B: Condensed Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.45.5585· OSTI ID:5000576

Wood, R F; Cooke, J F ^[1]

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1. Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6032 (United States)

The results of further studies of a {ital d}{sup 9} spin-polaron model of high-{ital T}{sub {ital c}} superconductivity are reported. Calculations of their formation energies suggest that spin polarons involving the Cu {ital d}{sup 9} configuration and O 2{ital p}{sigma} orbitals in the CuO{sub 2} planes should form readily in the high-{ital T}{sub {ital c}} superconductors. Estimates of their radii and effective masses indicate that they are small spin polarons with masses {similar to} four times the band effective mass. Formation of spin polarons destroys the long-range antiferromagnetic (AF) ordering but repair of the AF order locally provides a pairing mechanism. Parametrized AF band calculations for a CuO{sub 2} plane show how a Mott-Hubbard (MH) gap opens as a consequence of an electron repulsion energy {ital U} at the Cu sites. The parameters are chosen to give agreement with the measured density of states, the magnetic moment per Cu site, and other data. Variation of the hole concentration by Sr doping in La{sub 2{minus}{ital x}}Sr{sub {ital x}}CuO{sub 4} and O depletion in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} moves the Fermi level relative to the MH band edge. Approximate expressions for the gap and {ital T}{sub {ital c}} within the framework of a Cooper-pairing approach are derived and then solved using information from the band calculations. The proximity of the Fermi level to the MH band edge and the interplay of O 2{ital p}{sigma} and 2{ital p}{pi} bands and/or localization effects can provide good fits to the variations of {ital T}{sub {ital c}} with {ital x} in La{sub 2{minus}{ital x}}Sr{sub {ital x}}CuO{sub 4} and YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}}. The in-plane gap is either {ital s}- or {ital d}-like but anisotropic in either case. A discussion of various aspects and implications of the model is given.

• DOE Contract Number: AC05-84OR21400
• OSTI ID: 5000576
• Journal Information: Physical Review, B: Condensed Matter; (United States), Journal Name: Physical Review, B: Condensed Matter; (United States) Vol. 45:10; ISSN PRBMD; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360207* -- Ceramics
Cermets
& Refractories-- Superconducting Properties-- (1992-)
ALKALINE EARTH METAL COMPOUNDS
ALLOYS
ANTIFERROMAGNETISM
BARIUM COMPOUNDS
BARIUM OXIDES
BCS THEORY
CHALCOGENIDES
COOPER PAIRS
COPPER COMPOUNDS
COPPER OXIDES
D STATES
EFFECTIVE MASS
ENERGY LEVELS
FERMI LEVEL
HIGH-TC SUPERCONDUCTORS
HOLES
LANTHANUM COMPOUNDS
LANTHANUM OXIDES
MAGNETISM
MASS
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
P STATES
PEROVSKITE
PEROVSKITES
PHYSICAL PROPERTIES
POLARONS
QUASI PARTICLES
RARE EARTH COMPOUNDS
STRONTIUM ADDITIONS
STRONTIUM ALLOYS
SUBSTOICHIOMETRY
SUPERCONDUCTORS
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
TRANSITION TEMPERATURE
YTTRIUM COMPOUNDS
YTTRIUM OXIDES