Chinese Acad Sci, Inst High Energy Phys, Beijing Synchrotron Radiat Facil, Beijing 100039, Peoples R China
; Univ Roma La Sapienza, Unita INFM, I-00185 Rome, Italy
; Univ Roma La Sapienza, Dipartimento Fis, I-00185 Rome, Italy
; Ist Nazl Fis Nucl, Lab Nazl Frascati, I-00044 Frascati, Italy
The HgBa2CuO4+delta superconductor has been studied by high resolution Hg L-3 x-ray absorption near-edge structure (XANES) spectroscopy. The XANES spectrum has been simulated by full multiple-scattering calculations in order to explore the origin of different features in the experimental spectrum. The experimental Hg L-3-edge spectrum could be well reproduced by considering a cluster of 85 atoms, containing 10 shells, within a radius of about 7 Angstrom from the central Hg atom. The low energy spectral feature in the XANES spectrum is found to be due to a transition from the Hg p states to the electronic states hybridized with higher shell Ba atoms. This implies that the transition features in the Hg L3-edge XANES are strongly influenced by medium range order effects unlike the case of L-3 edge of 3d transition metals where short-range order is enough to describe the main transition features.