Charge dynamics of doped holes in high Tc cuprates - A clue from optical   conductivity
  The charge dynamics in weakly hole doped high temperature superconductors is studied in terms of the accurate numerical solution to a model of a single hole interacting with a quantum lattice in an antiferromagnetic background, and accurate far-infrared ellipsometry measurements. The experimentally observed two electronic bands in the infrared spectrum can be identified in terms of the interplay between the electron correlation and electron-phonon interaction resolving the long standing mystery of the mid-infrared band. 
A.S. Mishchenko, N. Nagaosa, Z.-X. Shen, G. De Filippis, V.   Cataudella, T.P. Devereaux, C. Bernhard, K.W. Kim, J. Zaanen