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Photoinduced absorption measurements of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ ($\ensuremath{\delta}=0.75$) from 150 to 4000 ${\mathrm{cm}}^{\ensuremath{-}1}$ are reported. We observed photoinduced infrared-active vibrational modes, associated phonon bleachings, and an electronic transition from a self-localized gap state. The results indicate a local tetragonal to orthorhombic distortion around the charge carriers. The dynamic mass associated with the distortion is smaller in $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ than in ${\mathrm{La}}_{2}$Cu${\mathrm{O}}_{4}$. The photoinduced structural distortion and the associated self-localized gap state demonstrate that the photoexcitations are polarons or bipolarons. Since these photoinduced absorption features are not observed in the isostructural compound ${\mathrm{La}}_{2}$Ni${\mathrm{O}}_{4}$ we conclude that polaron (or bipolaron) formation may play an important role in the high-temperature superconductivity.

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