S. A. Fefelov, L. P. Kazakova, S. A. Kozyukhin, K. D. Tsendin, D. Arsova, V. Pamukchieva, “Current-voltage characteristics of thin Ge$_2$Sb$_2$Te$_5$ films taken using a measuring circuit with a current source”, Zhurnal Tekhnicheskoi Fiziki, 84:4 (2014), 80–84; Tech. Phys., 59:4 (2014), 546–550
