Gauge-invariant and current-continuous microscopic ac quantum transport theoryJianQiao Zhang, ZhenYu Yin, Xiao Zheng, ChiYung Yam and GuanHua ChenEur. Phys. J. B, 86 10 (2013) 423DOI: https://doi.org/10.1140/epjb/e2013-40325-7