[en] Optical reflectance spectra in the range 30-35000 cm/sup -1/ and 4-300 K are presented on several YBa/sub 2/Cu/sub x/O/sub y/ phases, as well as different forms of the superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ phases (polycrystalline pellets, textured pellets with ab-plane oriented surface, and single crystals)

[en] The infrared vibrational spectra of the organic quasi-one dimensional charge transfer salts quinolinium (TCNQ)₂ and triethylammonium (TCNQ)₂ change markedly upon irradiation by high energy neutrons. A reduction of the intensity of some totally symmetric modes and an increase of visibility of other modes are observed in the irradiated samples. The results are discussed in the framework of the electron-vibrational interaction theory. The doses required to obtain observable changes are relatively high and point rather to a model of simple electron coupled vibrational modes extended over a few molecules than to phase oscillations of a collective state with a long coherence length. (author)

[en] New results covering a wide frequency and temperature range are presented for the infrared properties of YBa₂Cu₃O/sub 7-//sub δ/ for light polarized in the ab plane. The normal-state optical conductivity can be described by two processes: a low-frequency Drude absorption that tracks the temperature dependence of the dc conductivity and a temperature-independent midinfrared band. In the superconducting state most of the oscillator strength of the Drude absorption moves to zero frequency and the reflectance spectrum is dominated by a plasma edge at 500 cm/sup -1/. A superconducting gap cannot be seen in our spectra

[en] Thoul, Similon, and Sudan answer to the Comment by Terry, Diamond, and Hahm

[en] (110)-oriented superlattices of YBCO/PrBCO were grown successfully by laser ablation. Perfect in-plane alignment of the c-axis on the entire substrate surface allowed us to study the anisotropy of physical properties of these superlattices. 11 refs., 3 figs

[en] Optical and neutron-diffraction studies of superconducting and nonsuperconducting samples of YBa₂Cu₃O/sub 7-//sub y/ are described. Superconducting samples, with y≅0.1, showed two strong electronic transitions, at 3000 cm/sup -1//0.37 eV and at 20 000 cm/sup -1//2.5 eV, which are interpreted as charge-transfer bands (i.e., excitons). Nonsuperconducting samples, with y≅0.8 (prepared by heating of superconducting samples in vacuum to deplete the oxygen content), did not show these features. Our measurements support an excitonic mechanism for the superconductivity in high-T/sub c/ copper oxide compounds

[en] Polycrystalline samples of YBa/sub 2/Cu/sub 3/O/sub 7-δ/ with a variety of surface treatments show differences in absolute reflectance and width of phonon lines. Samples that are not polished and are measured immediately after annealing have largely grains with the c axis normal to the surface. Such oriented samples show a gap-like depression of conductivity in the far infrared that sets in below the superconducting transition temperature but no true gap. Phonon lines at 195 cm/sup -1/ and at 155 cm/sup -1/ narrow in the superconducting state, in analogy with the effect of the electron phonon interaction in BCS superconductors. In the normal state the background conductivity is Drude like with a plasma frequency of 0.75 eV and a relaxation rate of 200 cm/sup -1/. The extrapolated far-infrared conductivity agrees with the measured dc conductivity. In the following paper, the authors report on recent improvements in the measurement of the far-infrared optical properties of polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7-δ/. Initial measurements of the reflectance of superconducting YBa/sub 2/Cu/sub 3/O/sub 7-δ/ in the far infrared revealed a complex reflectance spectrum with very strong optically active phonons. A study of oriented samples is useful in deciphering the unusual behaviour of this material in the far infrared and demonstrates some of the difficulties in interpreting reflectance measurements

[en] Polycrystalline samples of YBa₂Cu₃O/sub 7-//sub δ/ with a variety of surface treatments show differences in absolute reflectance and width of phonon lines. Samples that are not polished and are measured immediately after annealing have largely grains with the c axis normal to the surface. Such oriented samples show a gaplike depression of conductivity in the far infrared that sets in below the superconducting transition temperature but no true gap. Phonon lines at 195 cm/sup -1/ and at 155 cm/sup -1/ narrow in the superconducting state, in analogy with the effect of the electron-phonon interaction in Bardeen-Cooper-Schrieffer superconductors. In the normal state the background conductivity is Drudelike with a plasma frequency of 0.75 eV and a relaxation rate of 200 cm/sup -1/. The extrapolated far-infrared conductivity agrees with the measured dc conductivity

[en] We present reflectance data for the high-temperature superconductor YBa₂Cu₃O₇, and the Kramers-Kronig transformed conductivity from 50 to 900 cm/sup -1/. There is a rich phonon structure with peaks at 151, 191, 279, 310, 548, and 609 cm/sup -1/. The continuous background is Drude type at high temperature but below the superconducting transition there is a region of suppressed conductivity consistent with a superconducting gap with the weak-coupling BCS value. Also associated with superconductivity are changes to the low-lying phonons and a plasma-type edge at 60 cm/sup -1/

[en] Polarized reflectance spectra of pure and neutron irradiated samples of oriented quinolinium (TCNQ)² mosaics (containing up to 8% radiation-induced impurities) were measured in the mid-infrared region (400-200 cm^-₁) in order to get information about the change occurring at IR frequencies in conducting uniform-stack salts upon irradiation. With increasing defect concentration a uniform stack is practically changed into an island-type one