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Author (up) Fainstein, A.; Etchegoin, P.; Guimpel, J.
Title Raman study of photoinduced chain-fragment ordering in GdBa2Cu3Ox thin films Type Journal Article
Year 1998 Publication PHYSICAL REVIEW B Abbreviated Journal
Volume 58 Issue 14 Pages 9433-9439
Keywords
Abstract Raman scattering experiments on oxygen deficient GdBa2Cu3Ox thin films (x=6.53, 6.7, 6.8, and 6.93) as a function of photoexcitation and annealing induced oxygen disorder are presented. Raman lines, unambiguously assigned to copper and oxygen vibrations involving atoms at the end of Cu-O chains, are used as markers for the existence of short chain fragments. The dynamics of chain conjunction and fragmentation was monitored by the peak intensity dependences with photoexcitation time and annealing temperature. These results demonstrate the presence of photoassisted oxygen ordering in these high-T-c superconductors, and give definitive support for its ultimate role in the phenomena of persistent photoconductivity and photoinduced superconductivity. [S0163-1829(98)04037-5].
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ISSN 0163-1829 ISBN Medium
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Notes ISI:000076486700083 Approved no
Call Number BT @ hernan @ Serial 183
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Author (up) Nöllmann, M.; Shalom, D.; Etchegoin, P.; Sereni, J.G.
Title Photobleaching and reorientational dynamics of dyes in a nematic liquid crystal Type Journal Article
Year 1999 Publication Physical Review E Abbreviated Journal Phys. Rev. E
Volume 59 Issue Pages 1850
Keywords
Abstract The polarized fluorescence of excited dyes in a prototype nematic liquid crystal is studied as a function of temperature, polarization of the light, and laser wavelength. We show explicitly the coexistence of photobleaching and dye diffusion through the nematic host as two mechanisms influencing the magnitude of the fluorescence signal. In addition, we exhibit clear evidence of the presence of a torque at low input laser powers that twist the dye molecules with respect to the director orientation of the liquid crystal, if the dyes are resonantly excited. The fluorescence emission in this latter case is able to perceive the birefringence of the nematic liquid crystal host, and this is shown as clear oscillations in the polarized fluorescence as a function of temperature. Extensive qualitative comparisons of the experimental results with the mean-field Maier-Saupe theory of the nematic state are presented, and a model is proposed to account for the observations.
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Notes Approved no
Call Number BT @ pedrazp @ Serial 686
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