1. Matthias, B.T.: Science 154 (1966) 543.
2. Fowler, R.D., Matthias, B.T., Asprey, L.B., Hill, H.H., Lindsay, J.D.G., Olsen, C.E., White, R.W.: Phys. Rev. Lett. 15 (1965) 860.
3. Hulm, J.K., Chandrasekhar, B.S.: LT-5 (1958) 280.
4. Eisenstein, J.: Rev. Mod. Phys. 26 (1954) 277.
5. Alekseyevsky, N., Migunov, L.: J. Phys. (Moscow) 11 (1947) 95.