1. Bednorz, J.G., Müller, K.A.: Z. Phys. B?Condensed Matter64, 189 (1986)
2. Aharony, A. Birgeneau, R.J., Kastner, M.A.: Z. Phys. B?Condensed Matter71, 57 (1988)
3. Caspary, R., Bredl, C.D., Spille, H., Winkelmann, M., Steglich, F., Schmidt, H., Wolf, T., Flükiger, R.: Physica C153?155, 876 (1988)
4. A short version will already be published in the Proceedings of the International Conference on Materials and Mechanisms of Superconductivity?High-Temperature Superconductors, Stanford, U.S.A., 1989
5. Caspary, R., Winkelmann, M., Steglich, F.: Physica C (1989)