Electron-energy-loss and optical-transmittance investigation of Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8

Journal Article · Sun Jul 01 00:00:00 EDT 1990 · Physical Review, B: Condensed Matter; (USA)

DOI:https://doi.org/10.1103/PhysRevB.42.420· OSTI ID:6826247

Wang, Y; Feng, G; Ritter, A L ^[1]

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1. Department of Physics, Virginia Tech, Blacksburg, Virginia 24061 (USA)

The energy-loss function Im({minus}1/{epsilon}) of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} has been measured over the range {ital E}{sub loss}=0.8 to 80 eV by transmission electron-energy-loss spectroscopy (EELS) (nonimaging). The energy and momentum resolution were 0.1 eV and 0.04 A{sup {minus}1}, respectively. The low-energy spectra ({ital E}{sub loss}{le}3 eV) were studied as a function of momentum transfer (0.1 A{sup {minus}1}{le}{ital q}{le}0.3 A{sup {minus}1}). A well-defined peak in the loss function at {ital E}{sub loss}{similar to}1 eV is observed to disperse with momentum proportional to {ital q}{sup 2}. This excitation is analyzed in terms of both an intracell, charge-transfer exciton model and the free-carrier (plasmon) model. The derived effective mass of the exciton {ital m}{sub tot}/{ital m}{congruent}1.0 is far too small for a localized exciton. Using the free-carrier model and random-phase-approximation expressions for the dispersion coefficient, the carrier density and carrier effective mass can be determined separately. From our data and similar measurements by Nuecker {ital et} {ital al}. (Phys. Rev. B 39, 12 379 (1989)), it is found that the effective mass roughly scales with carrier density. A heuristic model is introduced based on the assumption that low-energy gaps exist in portions of the Fermi surface due to structural instabilities. The model suggests how the effective mass could appear to scale with carrier density and why a single Drude term (with frequency-independent effective mass) does not describe the mid- to far-infrared optical spectra. Finally, the optical transmittance of the EELS sample was measured and the spectra analyzed in terms of the free-carrier model.

• OSTI ID: 6826247
• Journal Information: Physical Review, B: Condensed Matter; (USA), Vol. 42:1; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BISMUTH OXIDES
ELECTRONIC STRUCTURE
CALCIUM OXIDES
COPPER OXIDES
STRONTIUM OXIDES
CARRIER DENSITY
DISPERSION RELATIONS
EFFECTIVE MASS
ENERGY GAP
ENERGY-LOSS SPECTROSCOPY
EXCITONS
FERMI LEVEL
HIGH-TC SUPERCONDUCTORS
PLASMONS
RANDOM PHASE APPROXIMATION
ALKALINE EARTH METAL COMPOUNDS
BISMUTH COMPOUNDS
CALCIUM COMPOUNDS
CHALCOGENIDES
COPPER COMPOUNDS
ELECTRON SPECTROSCOPY
ENERGY LEVELS
MASS
OXIDES
OXYGEN COMPOUNDS
QUASI PARTICLES
SPECTROSCOPY
STRONTIUM COMPOUNDS
SUPERCONDUCTORS
TRANSITION ELEMENT COMPOUNDS
360204* - Ceramics
Cermets
& Refractories- Physical Properties