Molecular orbital excitations in cuprates
  We report resonant inelastic x-ray scattering studies of electronic excitations in a wide variety of cuprate compounds. Specifically, we focus on the charge-transfer type excitation of an electron from a bonding molecular orbital to an antibonding molecular orbital in a copper oxygen plaquette. Both the excitation energy and the amount of dispersion are found to increase significantly as the copper oxygen bond-length is reduced. We also find that the estimated bond-length dependence of the hopping integral t_pd is much stronger than that expected from tight-binding theory. 
Young-June Kim, J. P. Hill, G. D. Gu, F. C. Chou, S. Wakimoto, R. J.   Birgeneau, Seiki Komiya, Yoichi Ando, N. Motoyama, K....