1. D. N. Langenberg,Low Temperature Physics—LT14, M. Krusius and M. Vuorio, eds. (North-Holland, Amsterdam, 1975), Vol. 5, p. 223.
2. A. G. Aronov and B. Z. Spivak,Fiz. Nizk. Temp. 4, 1365 (1978) [Sov. J. Low Temp. Phys. 4, 641 (1979)].
3. G. Schön,Low Temperature Physics—LT16, W. G. Clark, ed. (North-Holland, Amsterdam, 1981), Vol. 3, p. 1677.
4. L. R. Testardi,Phys. Rev. B 4, 2189 (1971).
5. G. A. Sai-Halasz, C. C. Chi, A. Denenstein, and D. N. Langenberg,Phys. Rev. Lett. 33, 215 (1974).