POLARONS AND BIPOLARONS IN OXIDES

The physical properties of Frohlich polarons and bipolarons are review ed in relation to the recent experimental study of the mid-infrared ab sorption spectra nf high-T-c cuprate superconductors, in particular, o f Nd2CuO4-y, YBa2Cu3O6+x and La2CuO4+x. The spectral region studied is of particular relevance for the open question of the presence of pola rons and bipolarons in these materials, since it coincides with the fr equency region where polaron and bipolaron absorption is to be expecte d. In our view, the optical absorption spectra as observed in the dope d cuprates are a manifestation of the polaron type relaxed excited fin al states.