Many-Body Interactions in Condensed-Matters

In commemoration of the 50 years anniversary of Fujita‐Miyaszawa theory on the 3‐body interaction among nucleons, we would like to review on the phenomena inherent to many‐body interactions in condensed matters: (1) 3‐body non‐additive interaction among atoms which causes significant effect on the third order virial coefficient, (2) the many‐body (ring) exchange in the solid helium 3 which plays important role, and (3) effective long range interaction induced by the elastic interaction in spin‐crossover materials which causes a peculiar phase transition of the mean‐field universality class.