Figure 3: X-ray absorption spectroscopy at Ti L edge.
From: Suppression of the critical thickness threshold for conductivity at the LaAlO3/SrTiO3 interface
(a) Sketch of the X-ray absorption spectroscopy (XAS) process depicting the 2p→3d electronic transitions at the Ti L2,3 edge. (b) Scheme of the XAS measurement geometries with linearly horizontal (LH) and linearly vertical (LV) polarized light. The incident beam forms a 30° angle with the sample surface (x,y). (c) Experimentally measured isotropic signals (ISO) versus photon energy of a STO(001) substrate, and of various (Co/)LAO(n)/STO samples. Spectra acquired at 300 K in total electron yield mode. (d) The corresponding experimental X-ray linear dichroism (XLD) signals show a sign inversion between the XLD of STO and Co/STO and that of LAO(2,4 uc) and Co/LAO(2 uc) samples. (e) Calculated XLD that reproduces the experimental XLD of the STO bare substrate (circle, [A]) and of the Co/LAO(2 uc)/STO sample (square, [B]). (f) The cubic crystal field (CF) splits the Ti4+ 3d states into eg and t2g levels. A tetragonal CF further lifts the orbital degeneracy, with: [A] case of STO, [B] case of (Co/)LAO/STO.
