Far-infrared optical properties of high-temperature superconductors

Thesis/Dissertation · Sun Jan 01 04:00:00 EST 1989

OSTI ID:5962939

Rao, A M

Far infrared spectroscopy was used to investigate the optical properties of La{sub 2}CuO{sub 4} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} compounds. Room temperature reflectance measurements were carried out on La{sub 2-x}Sr{sub x}CuO{sub 4} polycrystalline pellets as a function of Sr concentration (z) and the spectra were analyzed using the effective medium approximation in which the anisotropy of the dielectric functions perpendicular and parallel to the CuO{sub 2} planes was taken into account. In this way, the origin of the spurious 0.4 eV peak obtained by others as a result of a Kramers-Kronig transformations of pellet data was explained. Neglecting the small orthorhombic distortion, a tetragonal crystal structure was considered and the ir-active in-plane (E{sub u} symmetry) and the out-of-plane (A{sub 2u} symmetry) phonon modes were established. The ab-plane Drude parameters and the dc conductivity ({sigma}{sub 0}) as a function of x were also obtained. Room temperature polarized reflectance measurements on single crystal La{sub 2}CuO{sub 4} revealed that the in-plane phonon frequencies could be reliably obtained from the polycrystalline samples, while the out-of-plane single-crystal data showed an additional mode than that observed in the pellet data. The presence of the extra mode may be due to the doubling of the tetragonal unit cell or due to the orthorhombic splitting of the zone centered phonons and theoretical work is in progress to verify the origin of the extra mode. Kramers-Kronig (KK) derived dielectric functions of the polarized La{sub 2}CuO{sub 4+y} reflectivity spectra does not show the 0.4 eV peak obtained from the KK transforms of the pellet data by others. The infrared reflectance of Bi{sub 2} Sr{sub 2}CaCu{sub 2} O{sub 8} thin films on SrTiO{sub 3} (001) substrates were studied as a function of temperature and a fit based on the Leplea's theory to the 5 K reflectance spectrum yields.

• Research Organization: Kentucky Univ., Lexington, KY (USA)
• OSTI ID: 5962939
• 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
AMBIENT TEMPERATURE
BISMUTH COMPOUNDS
BISMUTH OXIDES
CALCIUM COMPOUNDS
CALCIUM OXIDES
CHALCOGENIDES
COPPER COMPOUNDS
COPPER OXIDES
CORRELATIONS
CRYSTAL STRUCTURE
ELECTROMAGNETIC RADIATION
FAR INFRARED RADIATION
FILMS
INFRARED RADIATION
INFRARED SPECTRA
KRAMERS-KRONIG CORRELATION
LANTHANUM COMPOUNDS
LANTHANUM OXIDES
OPTICAL PROPERTIES
OXIDES
OXYGEN COMPOUNDS
PHONONS
PHYSICAL PROPERTIES
QUASI PARTICLES
RADIATIONS
RARE EARTH COMPOUNDS
SPECTRA
SPECTROSCOPY
STRONTIUM COMPOUNDS
STRONTIUM OXIDES
SUPERCONDUCTING FILMS
THIN FILMS
TRANSITION ELEMENT COMPOUNDS