1. G.A. Smolenskiy, V.A. Isupov, Tech. Phys. 24(8), 1375 (1954) (in Russian)
2. V.A. Isupov, Tech. Phys. 24(9), 1913 (1956) (in Russian)
3. G.A. Smolenskiy, V.A. Isupov, A.I. Agranovskaya, S.N. Popov, Phys. Solid State 2(11), 2906 (1960) (in Russian)
4. V.A. Isupov, Phys. Solid State 5(1), 187 (1963) (in Russian)
5. V.Y. Frizberg, B.N. Rolov, Izv. AN USSR. Ser. Phys. 28(4), 649 (1964) (in Russian)