Mott-Hubbard transition in alkali ammonia fullerides

摘要

Monoammoniated alkali fullerides salt (NH_3)K_(3-x)Rb_xC_(60) (0 < = x < = 3), forming an isostructual orthorhombic series followed by a Mott-Hubbard type antiferromagnetic transition. The Neel temperature T_N was found to first increase with the interfullerene spacing and then decreases for (NH_3)Rb_3C_(60), forming a maximum at 76K. This behavior can not be understood by a simple localized electron model and provides direct evidence for the important role of electron correlation effects.