Phonon anomalies and range of superconducting energy gaps from infrared studies of YBa/sub 2/Cu/sub 3/O/sub 7/minus//delta//

Journal Article · Tue Aug 01 04:00:00 EDT 1989 · Phys. Rev. B: Condens. Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.40.2170· OSTI ID:5947278

Genzel, L; Wittlin, A; Bauer, M; Cardona, M; Schonherr, E; Simon, A

The infrared reflectivity of sintered YBa/sub 2/Cu/sub 3/O/sub 7/minus//delta//, prepared under carefully controlled oxidation conditions, has been measured between 20 and 10 000 cm/sup /minus/1/ at temperatures between 10 and 300 K. In this paper we analyze in detail the temperature- and frequency-dependent far-infrared part of the spectrum. A Kramers-Kronig analysis allows us to compare the phonon part of the spectra with lattice-dynamical calculations. There is fairly good agreement concerning the assigned eigenfrequencies. The oscillator strengths of the experimentally observed phonons, however, are all stronger than those from a lattice-dynamics model which assumes ionic charges close to the formal ones. This is especially so for the lowest phonon found at 155 cm/sup /minus/1/ which shows a strength /ital S/=60/plus minus/5 being about 15 times higher than theoretically expected. A possible origin of this effect is discussed qualitatively in terms of a Cu(1)-O(IV) charge shift during the vibration induced by the polarization field. The electronic background of the spectra has been analyzed by a Mattis-Bardeen type of dielectric response below /ital T//sub /ital c//. The best fit yielded, for low /ital T/, a gap distribution in the range from about 160 to 370 cm/sup /minus/1/, corresponding to 2/Delta/(0)//ital k//sub /ital B//T/sub c/ values between 2.6 and 6.0.

• Research Organization: Max-Planck-Institut fur Festkorperforschung, Heisenbergstrasse 1, D-7000 Stuttgart 80, Federal Republic of Germany (DE)
• OSTI ID: 5947278
• Journal Information: Phys. Rev. B: Condens. Matter; (United States), Journal Name: Phys. Rev. B: Condens. Matter; (United States) Vol. 40:4; ISSN PRBMD
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
656100 -- Condensed Matter Physics-- Superconductivity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
BARIUM OXIDES
CHALCOGENIDES
COPPER COMPOUNDS
COPPER OXIDES
CORRELATIONS
ELECTROMAGNETIC RADIATION
ENERGY GAP
FAR INFRARED RADIATION
INFRARED RADIATION
KRAMERS-KRONIG CORRELATION
MATERIALS
OPTICAL PROPERTIES
OSCILLATOR STRENGTHS
OXIDES
OXYGEN COMPOUNDS
PHONONS
PHYSICAL PROPERTIES
PROBES
QUASI PARTICLES
RADIATIONS
REFLECTIVITY
SINTERED MATERIALS
SUPERCONDUCTORS
SURFACE PROPERTIES
TRANSITION ELEMENT COMPOUNDS
YTTRIUM COMPOUNDS
YTTRIUM OXIDES