1. Y.W. Tung and M.L. Cohen, Phys. Rev., to be published.
2. Intern. Coll. on IV-VI compounds;Cohen,1968
3. Technical Report No. HP-13;Prakash,1967
4. New Type of Negative Resistance in Barrier Tunneling
5. J.R. Burke and H.R. Riedl, to be published.