Local and nonlocal excitations in Cu 4p-1s resonant X-ray emission spectra of Nd2CuO4

Theoretical study for Cu 4p-1s resonant X-ray emission spectroscopy (RXES) of Nd2CuO4 is given in the context of local and nonlocal natures of electronic excitations. Detailed analyses with an impurity Anderson model and multi-Cu models are presented, based on exact diagonalization technique. By investigating partial densities of states, basic characters of each excited state are clarified. It is demonstrated that a disagreement with experimental data is unavoidable with the impurity model. The key concept to solve the difficulty is Zhang-Rice singlet formation in the intermediate state of RXES. We find that it survives in the final state of RXES as the lowest charge-transfer excitation. The limitation of the impurity model and the essential role of nonlocal excitations in RXES are stressed.