Magnetic RIXS on La 2 CuO 4

1. Probing magnons with X-rays Kramers-Heisenberg relation: Energy conservation Dipole operator Intermediate states with Detuning fromresonance Core-hole exists ashort time:  ≈ 2-3 eV Core-hole creates local potential from which electrons of the solid are scattered. System can be left behind in excited state.  One measures elementary excitations of the solid! 3d electrons J modified bycore-hole potential Core hole Conclusions & Outlook F. Forte, L.J.P. Ament, J. van den Brink Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherlands Indirect RIXS Theory Synchrotron radiation Momentum transfer q & Energy loss  Unoccupied valence level 4p wres (5-10 KeV) 1s Core level Magnetic RIXS on La2CuO4 Theory applied to La2CuO4 La2CuO4: 3d electrons on Cu form Mott-Hubbard insulator  effective Heisenberg Hamiltonian: initial intermediate final 4p 4p 4p 3d 3d 3d 1s 1s 1s Core-hole qin , win qout , wout  qin, win Elementary excitations are magnons. Conservation of Sz only 2-magnon processes allowed! Core-hole modifies superexchange interaction Jij Results Theoretical predictions  > En: we can resum Afi and retain the leading order term in J’/: ExperimentTheoryTheory + exp. resolution a 4-spin correlation function! We used linear spin-wave theory to obtain the spectra. We established a general procedure to find indirect RIXS spectra. Application to La2CuO4 shows: 1. Only 2-magnon processes allowed2. Quantitative agreement with experiments3. RIXS complements neutron scattering (2-spin correlation functions) The next step will be to apply this theory to other elementary excitations like orbital waves. At q = (0,0) there is no energy loss: RIXS intensity = 0. Experiments: J.P. Hill et al.1,magnetic parameters from neutron scattering2. No free magnetic parameters! 1Unpublished 2Coldea et al. Phys. Rev. Lett. 86, 5377 (2001)