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A. A. Antoniou and J. A. Morrison,J. Appl. Phys. 36, 1873 (1965).
D. Redfield,Phys. Rev. Letters. 27, 730 (1971).
V. Narayanamurti and R. O. Pohl,Rev. Mod. Phys. 42, 201 (1970).
W. A. Phillips,Proc. Roy. Soc. (London)A319, 565 (1970).
P. W. Anderson, B. I. Halperin, and C. M. Varma, to be published.
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W. A. Phillips,Phys. Rev. B 3, 12 (1971).
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Fulde and WagnerPhys. Rev. Letters,27, 1280, (1971).
