Unique identification of Zhang-Rice singlet excitation in Sr2CuO2Cl2 mediated by the O 1s core hole:: Symmetry-selective resonant soft x-ray Raman scattering study -: art. no. 165104

Zhang-Rice singlet excitation around 2 eV is observed, distinguished from Cu dd excitations, by a symmetry selective resonant soft x-ray Raman scattering (RSXRS) experiments at the O 1s edge excitation of Sr2CuO2Cl2. Well below Neel temperature the initial state of Sr2CuO2Cl2 is antiferromagnetic, and then the final state with the Zhang-Rice singlet is excited selectively when the photon polarization is conserved in the RSXRS process. We also observe a weak RSXRS structures around 0.5 eV in the controversial midinfrared region, taking advantage of extremely weak elastic scattering intensity in the O 1s edge. From its polarization dependence, it is interpreted to originate mainly from the two-spin-flip excitations.