Photoinduced Self-Localized Structural Distortions in YBa2Cu3O7-delta: Direct Evidence of Polarons or Bipolarons
CALIFORNIA UNIV SANTA BARBARA DEPT OF CHEMISTRY
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Photoinduced infrared absorption measurements of YBa2Cu307-delta delta0.75 in the spectral region from 150cm to 4000 cm are reported. We observed photoinduced infrared active vibrations IRAV modes, associated phonon bleachings, and an electronic transition from a localized gap state peaked at 1050cm 0.13 eV. The spectral features indicate a local tetragonal to orthorhombic distortion in the Cu-O plane around the photoinduced charge carriers in YBa2Cu307-delta is smaller than La2CuO4. The photoinduced structural distortion and the associated self-localized gap state demonstrate that the photoexcitations are relatively long lived polarons or bipolarons.
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