RESUMO
X-ray absorption near-edge structure (XANES) spectroscopy has been used to investigate the unoccupied electronic states and local geometry of Ir1-xPtxTe2(x = 0.0, 0.03 and 0.04) as a function of temperature. The Ir L3-edge absorption white line, as well as high energy XANES features due to the photoelectron multiple scatterings with near neighbours, reveal clear changes in the unoccupied 5d-electronic states and the local geometry with Pt substitution. We find an anomalous spectral weight transfer across the known first-order structural phase transition from the trigonal to monoclinic phase in IrTe2, which characterizes the reduced atomic structure symmetry below the transition temperature. No such changes with temperature are seen in the Pt substituted superconducting samples. In addition, a gradual increase of the spectral weight transfer is observed in IrTe2 with a further decrease in temperature below the transition, indicating that the low temperature phase is likely to have a symmetry lower than the monoclinic one. The results suggest that the interplay between inter-layer and intra-layer atomic correlations should have a significant role in the properties of an Ir1-xPtxTe2 system.
RESUMO
In-plane polarized Cu K-edge XAFS on La2CuO4.1 is presented, which indicates a radial in-plane Cu-O distribution function that is not a single Gaussian. Fits to the isolated Cu-O XAFS signal show the presence of a two-site radial distribution function, similar to that found in other La-based cuprate superconductors at temperatures below the temperature associated with the pseudogap appearance, T*. The appearance of the two-site distribution is interpreted as evidence of a non-homogeneous ground state, preceding the superconducting transition. Similar results found in other copper-oxide superconductors indicate that this non-homogeneous ground state is a general feature of these materials.
