1. P.A. Lee, T.M. Rice, J.M. Serene, L.J. Sham, J.W. Wilkins: Comments Condensed Matter Phys. 12, 99 (1986)
2. P. Fulde, J. Keller, G. Zwicknagl: In Solid State Physics, Vol. 41, ed. by H. Ehrenreich, D. Turnbull (Academic, San Diego 1988) p. 1
3. P. Schottmann: Phys. Rep. 181, 1 (1989)
4. G. Zwicknagl: Adv. Phys. 41, 203 (1992)
5. M.R. Norman, D. Koelling: In Handbook on the Physics and Chemistry of Rare Earths, Vol. 17, ed. by K.A. Gschneidner, L. Eyring, G.H. Lander, G.R. Choppin (Elsevier, Amsterdam 1993) p. 1