Current-Induced Reversible Resistance Jumps in La0.8Ca0.2MnO3 Microbridge*Supported by the National Natural Science Foundation of China under Grant Nos U1332205, 11404169 and 11274153, the Natural Science Foundation of Jiangsu Province under Grant No BK20140450, and the Huaian Science and Technology (Industry) Project under Grant No HAG2014043. (May 2016)