Magnetic RIXS on La2CuO4

1
Probing magnons with X-rays
F. Forte, L.J.P. Ament, J. van den Brink
Instituut-Lorentz, Universiteit Leiden, P.O. Box
9506, 2300 RA Leiden, The Netherlands
Theory
Indirect RIXS
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
? gt 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)