Photovoltaic effect in iron-based SmO_0.7F_0.3FeAs superconductors

A remarkable photovoltaic effect in an iron-based SmO_0.7F_0.3FeAs–Ag system has been observed in the temperature range from 50 to 300 K. An interface potential exists directly from the superconductor to the metal electrode, which provides the separation force for the photo-induced electron–hole pairs. The mechanism of this interface potential is completely different below and above the superconducting transition temperature and has been discussed in terms of the proximity effect and Schottky barrier, respectively. In contrast to that found in the YBCO-Ag system, a photovoltaic effect of opposite polarity is obtained in a SmO_0.7F_0.3FeAs–Ag system at a normal state, consistent with the different type of charge carriers in these two superconductors. A very fast laser response (7.5 ms) may open a door to new device applications such as optical sensors. (paper)