Momentum-resolved charge and spin excitations in cuprate superconductors

In the last two decades, energy resolution of resonant inelastic x-ray scattering (RIXS) has been significantly improved, and RIXS is now established as a momentum-resolved spectroscopy using synchrotron radiation x-rays. Since the beginning of RIXS, cuprate superconductors have been intensively studied. In addition to the interest of superconductivity at the high transition temperature and related phenomena, such as pseudogap and a competing phase with charge order, doped cuprates are important and suitable for the study of the electronic structure of the doped Mott insulator. This is because relatively simple theoretical models with a few orbitals are applicable to describe the electronic structure near the Fermi energy. I will present charge and spin excitations in cuprates observed with RIXS at Cu K-, Cu L3- and O K-edges focusing on the energy range from eV to sub-eV. In this range, charge and spin excitations show characteristic momentum dependence with respective energy scale of hopping energy of electron (t) and exchange interaction of spin (J).