{ital c}-axis optical spectra and charge dynamics in La{sub 2{minus}{ital x}}Sr{sub {ital x}}CuO{sub 4}
- Department of Superconductivity, University of Tokyo, Yayoi 2-11-16, Bunkyo-ku, Tokyo 113 (Japan)
- Superconductivity Research Laboratory, ISTEC, Shinonome 1-10-13, Koto-ku, Tokyo 135 (Japan)
Out-of-plane ({ital c}-axis-polarized) optical reflectivity spectra and {ital c}-axis charge transport properties are studied for single crystals of a high-{ital T}{sub {ital c}} system La{sub 2{minus}{ital x}}Sr{sub {ital x}}CuO{sub 4} over a wide compositional range 0{le}{ital x}{le}0.30. The measurements are made at various temperatures in the normal and superconducting states over an energy range from 0.003 to 40 eV. The present study focuses on the evolution of the {ital c}-axis spectrum with doping and provides a full set of the optical and transport data on this single-layer system together with the previously published data of the in-plane spectra. As in the case of the in-plane spectrum, the spectral weight is transferred upon doping from the high- to low-energy region. Different from the in-plane spectrum the transferred weight forms a band which is centered at relatively high energy ({approximately} 2 eV) and does not appreciably move with increasing {ital x}. As a consequence, the {ital c}-axis optical conductivity [{sigma}{sub {ital c}}({omega})] is extremely small in the lowest-energy region ({lt}0.3 eV) until the compound is overdoped. Particularly, in the underdoped regime ({ital x}{lt}0.13) the low-energy {sigma}{sub {ital c}}({omega}) is too small to form a Drude peak, and is further suppressed with reducing temperature. This is in common with the pseudogap effect, observed for the bilayer system YBa{sub 2}Cu{sub 3}O{sub 6+{ital x}}, and is connected to the semiconducting {ital c}-axis resistivity. A Drude peak in {sigma}{sub {ital c}}({omega}) develops only in the highly doped compounds ({ital x}{ge}0.18). Only in the overdoped regime is {sigma}{sub {ital c}}({omega}) dominated by a sharp Drude term and the anisotropic resistivity {rho}{sub {ital c}}/{rho}{sub {ital ab}} almost constant over a wide temperature range, giving strong evidence for a three-dimensional metallic state.
- OSTI ID:
- 286172
- Journal Information:
- Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 21 Vol. 53; ISSN PRBMDO; ISSN 0163-1829
- Country of Publication:
- United States
- Language:
- English
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