1. P. E. Cladis, Philos. Mag. 29, 641 (1975).PHMAA40031-8086
2. S. Torza and P. E. Cladis, Phys. Rev. Lett. 32, 1406 (1974).PRLTAO0031-9007
3. F. Kahn, Appl. Phys. Lett. 22, 386 (1973).APPLAB0003-6951
4. F. Grandjean, Bull. Soc. Fr. Mineral. 42, 42 (1919).BSFMAU0366-3248
5. L. Cheung, thesis (Harvard University, 1974) (unpublished);