PHOTOINDUCED CHANGES IN RAMAN-SPECTRA OF YBA2CU3O6.4 FILMS

The evolution of Raman spectra with illumination has been studied in Y Ba2Cu3O6.4 films at temperatures between 5-300 K. Low laser power has always been used to avoid local overheating, which was controlled by m easuring the local temperature by the Stokes/anti-Stokes ratio. Three important photoinduced effects have been found: (i) the enhancement of the intensity of the observed phonon modes: (Cu(2) at 141 cm-1, O(2)- O(3) at 338 cm-1, and O(4) at 488 cm-1), which may be related to the o rdering of oxygen vacancies, (ii) the increase of the electronic scatt ering background for low Raman frequencies omega, which is in agreemen t with the enhancement of the static conductivity sigma(omega --> 0) a fter illumination, and (iii) the suppression of the intensity of the t wo-magnon band, which may be caused by the increase of charge carriers due to photodoping.