Electron-phonon coupling, oxygen isotope effect, and superconductivity in Ba sub 1-x K sub x BiO sub 3

Conference · Mon Jan 01 04:00:00 EST 1990

OSTI ID:5752572

Loong, C K; Hinks, D G; Degani, M H; Price, D L; Jorgensen, J D; Mitchell, A W ^[1]; Jin, W; Dabrowski, B; Richards, D R; Zheng, Y ^[2]; Vashishta, P; Kalia, R K ^[3]

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1. Argonne National Lab., IL (USA)
2. Science and Technology Center for Superconductivity (USA)
3. Louisiana State Univ., Baton Rouge, LA (USA)

The phonon spectra of superconducting Ba{sub 1-x}K{sub x}Bi{sup 16}O{sub 3} and Ba{sub 1-x}K{sub x}Bi{sup 16}O{sub 3} (x=0.4) and insulating Ba{sub 1-x}K{sub x}BiO{sub 3} (x=0, 0.2) are studied by inelastic neutron scattering (INS) and molecular dynamics (MD) simulations. The phonon densities-of-states (DOS) of the insulating materials exhibit peaks at 15, 35, 43, 63 and 70 MeV. In superconducting Ba{sub 1-x}K{sub x}BiO{sub 3}, the phonon spectrum softens and is comprised of three broad bands around 15, 30 and 60 MeV. The reference isotope-effect exponent of Ba{sub 0.6}K{sub 0.4}BiO{sub 3}, determined from the mass variation of the first frequency moment of the phonon DOS, is close to the oxygen isotope-effect exponent obtained from {Tc} measurements. Using the INS and MD results and a model for the spectral function {alpha}{sup 2} ({omega})F({omega}), the energy gap, critical temperature, electron tunneling spectra and the oxygen isotope-effect exponent are calculated based on the BCS-Eliashberg theory. The results indicate that Ba{sub 1-x}K{sub x}Bi{sup 16}O{sub 3} is a BCS weak-coupling superconductor. The high {Tc} (30 K) results from large electron-phonon coupling matrix elements involving high-energy oxygen optic phonons. 24 refs., 8 figs.

• Research Organization: Argonne National Lab., IL (USA)
• Sponsoring Organization: DOE; NSF; USDOE, Washington, DC (USA); National Science Foundation, Washington, DC (USA)
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 5752572
• Report Number(s): ANL/CP-72358; CONF-901291--1; ON: DE91011159; CNN: DMR88-09854
• Country of Publication: United States
• Language: English

Related Subjects

426001* -- Engineering-- Superconducting Devices & Circuits-- (1990-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
BARIUM OXIDES
BISMUTH COMPOUNDS
BISMUTH OXIDES
CHALCOGENIDES
ENERGY GAP
ENERGY-LEVEL DENSITY
GORKOV-ELIASHBERG THEORY
INELASTIC SCATTERING
ISOTOPE EFFECTS
ISOTOPES
MATHEMATICAL MODELS
NEUTRON SPECTRA
NUCLEAR MODELS
OXIDES
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PHONONS
PHYSICAL PROPERTIES
QUASI PARTICLES
SCATTERING
SPECTRA
SUPERCONDUCTORS
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE
TUNNEL EFFECT
WEAK-COUPLING MODEL