Origin of the anomalous photovoltaic signal in Y-Ba-Cu-O

The temperature and polarization dependence, and anisotropy of the laser-generated voltage response in Y-Ba-Cu-O under no-current-bias conditions were examined. It was found that the photogenerated current flowed predominantly along the c axis of the Y-Ba-Cu-O crystal, and was laser-polarization independent. The strong temperature dependence observed indicated that the signal was related to the 240-K structural transformation which was also responsible for other anomalies in the early days of Y-Ba-Cu-O research. The anomalous photovoltaic response is due to an asymmetry along the c axis of the Y-Ba-Cu-O orthorhombic crystalline structure.