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4. In addition we have investigated a sample withD Nb=1550 ?m andd Cu=890 ?m, produced by starting from the same initial dimensions as for our main sample. But the data for this sample indicate that its breakdown fieldH b is so small (probably <0.2 mG) that our field shielding (?0.1 mG) was not adequate to allow this sample to develop its full proximity effect
5. Gloos, K., Smeibidl, P., Kennedy, C., Singsaas, A., sekowski, P., Mueller, R.M., Pobell, F.: J. Low Temp. Phys.73, 101 (1988)