Zooming-in on the charge ordering in YBa2Cu3O6.5
  We report direct evidence of charge/orbital ordering of low energy electronic states of $Cu$ in YBa$_2$Cu$_3$O$_{6+x}$ ortho-II phase in both the $CuO_3$ chain and the CuO$_2$ plane. Huge enhancement of the $({1/2},0,0)$ superstructure Bragg peak is observed when photon energy is tuned to the $Cu L_{2,3}$ absorption edge with large polarization dependence. The ordering in the $CuO_2$ plane discovered here sheds new light on how the one dimensional $Cu-O$ chains affect the $CuO_2$ plane, and why many normal and superconducting state properties of this system exhibit strong anisotropy. 
D. L. Feng, A. Rusydi, P. Abbamonte, L. Venema, I. Elfimov, R. Liang,   D. A. Bonn, W. N. Hardy, C. Schusler-Langeheine, S. ...