Abstract
Resonant inelastic X-ray scattering (RIXS), a photon-in and photon-out spectroscopy method, has been used to probe two representative compounds, the optimally doped superconducting cuprate Bi1.5Pb0.6Sr1.54CaCu2O8+δ (Bi2212) and the first magnetic material found by mankind - magnetite Fe3O4. Investigation of collective magnetic excitations in cuprate superconductors is an important subject in searching the paring mechanism of high Tc superconductivity. In comparison with inelastic neutron scattering, RIXS reveals the existence of high-energy magnetic excitations in doped superconducting cuprates. However, the interpretation of such excitations remains in dispute. Here we show the dependence of Cu L3 RIXS on the energy and polarization of incident photons in optimally doped high-Tc cuprate superconductors Bi2212. Two distinct types of excitations, Raman-like and fluorescence-like, were observed by using π- and σ-polarized incident X-rays, respectively. Combined with calculations of exact diagonalization, we demonstrate the nature of collective damped magnetic excitations measured with -polarized RIXS. Fe3O4 has been studied for decades to understand the Verwey transition. The mech- anism of the simultaneous drop of electric conductivity and a complex structural phase transition has been one of the most extensively studied problems in condensed matter physics. We used RIXS to unravel the local electronic structures of diff erent Fe sites in Fe3O4. Local spin excitations are observed on the octahedral Fe3+ sites with an eff ective exchange field of 90 meV. Markedly we found a broad excitation feature with an energyof 200 meV for Fe2+. With the help of multiplet calculations, a tetragonal distortion of strength t2g = ?24 meV on the t2g orbitals was deduced. Our temperature-dependent RIXS spectra indicate that such local distortion already exists above the Verwey transition temperature and even up to 475 K.