Spectral evolution in (Ca,Sr)RuO_3 near the Mott-Hubbard transition
  We investigated the optical properties of (Ca,Sr)RuO_3 films on the borderline of a metal-insulator (M-I) transition. Our results show all of the predicted characteristics for a metallic Mott-Hubbard system, including (i) a mass enhancement in dc-limit, (ii) an U/2 excitation, and (iii) an U excitation. Also, a self-consistency is found within the Gutzwiller-Brinkman-Rice picture for the Mott transition. Our finding displays that electron correlation should be important even in 4d materials. 
J. S. Ahn, J. Bak, H. S. Choi, T. W. Noh (Seoul Nat'l U., Korea), J.   E. Han (Max-Planck Inst., Germany), Yunkyu Bang (Chon...