Photogeneration of Self-Localized Polarons in YBa2 Cu307-delta and La2 Cu04

摘要

Photoinduced infrared absorption measurements of YBa2Cu3O7-delta (delta=0.75) and La2CuO4 are reported. We have observed photoinduced infrared active vibrational modes and associated phonon bleachings which indicate the formation of a localized structural distortion in the Cu-O plane around the photogenerated carriers. In both materials, an associated electronic transition indicates that this structural distortion causes the formation of a self-localized electronic state in the energy gap. The photoinduced distortion and the associated self-localized gap state demonstrate that the photoexcitations are relatively long-lived polarons (or bipolarons). The dynamic mass associated with the distortion is smaller in YBa2Cu3O7-delta than in La2CuO4 (smaller dynamic mass implies a longer range distortion). Since these features are not observed in the isostructural compound, La2NiO4, we suggest that polaron (or bipolaron) formation may play an important role in the high temperature superconductivity. Superconductor, Polarons, Infrared, Superconductors. (MJM)