H. X. Liang, L. Cheng, X. F. Zhai, N. Pan, H. L. Guo, J. Zhao, H. Zhang, L. Li, X. Q. Zhang, X. P. Wang, C. G. Zeng, Z. Y. Zhang, J. G. Hou, Giant photovoltaic effects driven by residual polar field within unit-cell-scale LaAlO3 films on SrTiO3