Positron-annihilation momentum density in superconductors

Journal Article · Thu Feb 01 04:00:00 EST 1990 · Physical Review, B: Condensed Matter; (USA)

DOI:https://doi.org/10.1103/PhysRevB.41.1789· OSTI ID:7160780

Benedek, R ^[1]; Schuettler, H ^[2]

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1. Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (USA)
2. Center for Simulational Physics, Department of Physics and Astronomy, University of Georgia, Athens, Georgia 30602 (USA) Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (USA)

The origin of the dramatic shifts observed in the temperature dependence of positron-annihilation characteristics (particularly lifetime and Doppler-broadening line shape) near {ital T}{sub {ital c}} in the cuprates is not presently clear. Both intrinsic and extrinsic (i.e., defect-related) mechanisms have been proposed. To help clarify whether Cooper pairing is responsible for these shifts, we present an approximate formulation of the positron characteristics in a BCS superconductor. Relations are derived for the zeroth- and first-order terms in the ladder summation for the two-photon momentum density, with electron propagators represented in the Nambu-Gorkov form. The momentum densities in the normal and superconducting states differ appreciably only within the pairing shell centered at {ital p}{sub {ital F}}. Numerical calculations are performed for two- and three-dimensional models. The differences increase with increasing {Delta}/{mu} but are relatively small in the first-order calculation. We also estimate an upper bound to the effect of BCS pairing on the positron characteristics, including terms to all orders in the electron-positron interaction. Based on comparisons of our model calculations with experiment, it seems unlikely that BCS pairing is responsible for the measured shifts in positron properties near {ital T}{sub {ital c}}.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 7160780
• Journal Information: Physical Review, B: Condensed Matter; (USA), Journal Name: Physical Review, B: Condensed Matter; (USA) Vol. 41:4; ISSN 0163-1829; ISSN PRBMD
• Country of Publication: United States
• Language: English

Related Subjects

656100* -- Condensed Matter Physics-- Superconductivity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ANNIHILATION
ANTILEPTONS
ANTIMATTER
ANTIPARTICLES
BASIC INTERACTIONS
BCS THEORY
DOPPLER EFFECT
ELECTROMAGNETIC INTERACTIONS
ELEMENTARY PARTICLES
FERMIONS
INTERACTIONS
LEPTONS
LIFETIME
PHASE TRANSFORMATIONS
POSITRONS
SOLIDS
SUPERCONDUCTORS