Unoccupied electronic structure of TiOCl studied by x-ray absorption   near-edge spectroscopy
  We study the unoccupied electronic structure of the spin-1/2 quantum magnet TiOCl by x-ray absorption near-edge spectroscopy (XANES) at the Ti L and O K edges. Data is acquired both in total electron and fluorescence yield mode (TEY and FY, respectively). While only the latter allows to access the unconventional low-temperature spin-Peierls (SP) phase of TiOCl the signal is found to suffer from significant self-absorption in this case. Nevertheless, we conclude from FY data that effects of the SP distortion on the electronic structure are absent within experimental accuracy. The similarity of room-temperature FY and TEY data, the latter not being obscured by self-absorption, allows us to use TEY spectra for comparison with simulations. These are performed by cluster calculations in D$_{4h}$ and D$_{2h}$ symmetries using two different codes. We extract values of the crystal-field splitting (CFS) and parametrize our results in often found notations by Slater, Racah and Butler. In all cases, good agreement with published values from other studies is found. 
Sebastian Glawion, Maurits W. Haverkort, G\"otz Berner, Markus   Hoinkis, Gianina Gavrila, Roberto Kraus, Martin Knupfer, Mi...
cond-mat.str-el