Effects of non-equilibrium structure and temperature on photoinduced changes in optical transmission of Y Ba2 Cu3 O6,35 film

Sharp (∼ 25%) photoinduced changes in the optical transmission of the Y Ba2 Cu3 O6,35 film, which are non-linearly dependent on the irradiation time, are found at low temperatures. T<125 K, and low light flows (∼ 1013 photon/cm2 centre dot s). The conditions are studied under which the non-linear changes in transmission transform into a linear law. The analysis of the effect based on correlation between the optic transition intensity and the changing electron (hole) concentration in the Cu O2 plane permits the conclusion that (i) the degree of the sample ortho-nonequilibrium is the critical condition for effective photo pumping of the carriers under low-dose irradiation at low temperatures, (ii) the photopumping enhances the relaxation to the equilibrium ortho-ordering in the Cu Ox chains under the condition of non-linear photoinduced changes, (iii) on photodoping with light flows above the metallization threshold, two channels of the electron transition from Cu O2 to Cu Ox are in simultaneous operation - one is for the photoelectrons and the other is for the electron from the Fermi level of the Cu O2 plane. At 125 K the heavily pumped film undergoes a structural order-disorder transition during which the photopumped electrons (holes) are released as the temperature rises