Optical evidence for compatibility of antiferromagnetism and superconductivity in YBa2Cu3O6+x

The evolution of the spectral composition of the absorption in the 1.25-2.6 eV region for metallic films of YBa2Cu3O6+x with superconducting transition temperatures of T-c=51 and 74 K is measured as the films are cooled from 180 to 20 K. Particular attention is paid to the temperature effects in two absorption bands: the A band (similar or equal to1.8 eV), which reflects the appearance of holes dressed in antiferromagnetic (AFM) fluctuations, and the (A+J) band (similar or equal to2.15 eV), which reflects an additional (magnon) excitation of the short-range AFM order. It is found that the changes of these bands begin in the normal phase at T <T* in the temperature region corresponding to the opening of the pseudogap state, and the (A+J) magnon band arises in the pseudogap state even in the case when it is absent at room temperatures. At the superconducting transition the parameters of the bands stop changing, and the (A+J) magnon band is preserved in the superconducting state. The results are interpreted as evidence of a magnetic nature of the pseudogap state and for the compatibility of AFM short-range order with superconductivity. (C) 2000 American Institute of Physics. [S1063-777X(00)00511-9].