SPECULATIONS ABOUT GREY TIN.
CALIFORNIA UNIV SAN DIEGO LA JOLLA DEPT OF PHYSICS
Pagination or Media Count:
Groves and Paul have, on the basis of experimental evidence, given strong arguments that in grey tin the valence and conduction bands touch at k o. This suggests that at sufficiently low temperatures this phase may undergo an excitonic transition. The critical temperature may be estimated from the binding energy E sub B of an exciton kT sub c approximately equals E sub B mumepsilon squared Rydbergs, where mu is an effective reduced mass and epsilon is an effective dielectric constant. From the work of Groves and Paul and of Ewald and co-workers it is possible to estimate mum at about 0.02. If one accepts the estimate epsilon 24 given by Lindquist and Ewald one finds T sub C approximately equals 5 degrees K. From group theoretical considerations one finds that the new phase would belong to one of three space groups of lower symmetry and in one case would be weakly ferromagnetic. These conclusions are however highly tentative because of uncertainty about the dielectric constant epsilon and the suppression of the transition by small concentrations of impurities. Experimental studies of the dielectric constant epsilonomega would be highly desirable and interesting. Author
- Solid State Physics