Angular-Dependence in the K Pre-Edge XANES of Cubic Crystals : The Separation of the Empty Metal eg and t2g States of NiO and FeO

It is well known that by applying the angular dependence of the dipole transition matrix elements on the K XANES of single-crystal samples, the different pm-like DOS components (m = x,y,z) of the empty states can be well resolved. Analyzing quadrupole transitions in the pre-edge absorption region allows to fulfill a symmetry resolution of the different dm-states (m = xy ,xz, yz,x2-y2,z2). This has been done for the first time at the cubic single-crystals NiO and FeO, where we could differentiate between eg and t2g components of the empty states using the orientation dependence of the absorption spectra. The Cu K XANES of tetragonal Bi2Sr2CaCU2O8 could be also resolved into the nondegenerated pm- and dm-like components. The method will be demonstrated and results for NiO, FeO and Bi2Sr2CaCU2O8 are presented and discussed