Dynamics of charge carriers in cuprates

Detailed photoinduced infrared absorption studies of semiconducting Y1Ba2Cu3O6+y (y<0.2) and La2CuO4 were carried out. We observed two broad absorptions, one at ∼ 0.13 eV and the other at ∼ 0.62 eV in the photoinduced absorption spectrum of Y1Ba2Cu3O6+y in contrast to the previous photoexcitation results. We found that the lower energy peak positions in both Y1Ba2Cu3O6+y and La2CuO4 abruptly change at T - Tc of the corresponding superconducting phase. The amount of energy shift seems to be related to the pairing energy. Carrier recombination dynamics studies suggest that the ground state of photocarriers in the CuO2 plane at T < Tc is remarkably different from that observed a T > Tc.