1. D.L. Khomskii, Quantum Theory of Solids, edited by I.M. Lifshitz (Mir, Moscow 1982)
2. A. Jayaraman, in Handbook on the Physics, Chemistry of Rare Earth, edited by K. A. Gschneider, L. R. Eyring (North-Holland, Amsterdam, 1979), Vol. 2
3. P. Wachter, in Handbook on the Physics, Chemistry of Rare Earth, edited by K. A. Gschneider, L. R. Eyring (North-Holland, Amsterdam, 1994), Vol. 19
4. L.M. Falicov, J.C. Kimball, Phys. Rev. Lett. 22, 997 (1969)
5. P.W. Anderson, Phys. Rev. 124, 41 (1961)