1. J.-M, Triscone, O. Fischer, O. Brunner, L. Antognazza and A.D. Kent, Phys. Rev. Lett. 64, 804 (1990).
2. C.L. Jia, B. Kabius, H. Soltner, U. Poppe, K. Urban, J. Schubert and Ch. Buchal, Physica C 167, 463 (1990).
3. T. Venkatesan, I. Inam, B. Dutta, R. Ramesh, M.S. Hegde, X.D. Wu, L.Nazar, C.C. Chang, J.B. Barner, D.M. Hwang, and C.T. Rogers, Apple. Phys. Lett. 56, 391 (1990).
4. H. Obara, S. Kosaka, M. Umeda and Y. Kimura, Advances in Superconductivity II (Springer, Tokyo, 1990 ), p. 801.
5. D.W. Cooke, R.S. Kwok, E.L.Lichati, T.R Adams C. Boekema, W.K. Dawson, A. Kebede, J. Schwegier, J.E. Crow and T.Mihalisin: Phys. Rev. B41, 4801 (1990).