7 research outputs found
Ultrashort Lifetime Expansion for Indirect Resonant Inelastic X-ray Scattering
In indirect resonant inelastic X-ray scattering (RIXS) an intermediate state
is created with a core-hole that has a ultrashort lifetime. The core-hole
potential therefore acts as a femtosecond pulse on the valence electrons. We
show that this fact can be exploited to integrate out the intermediate states
from the expressions for the scattering cross section. By this we obtain an
effective scattering cross section that only contains the initial and final
scattering states. We derive in detail the effective cross section which turns
out to be a resonant scattering factor times a linear combination of the charge
response function and the dynamic longitudinal spin density
correlation function. This result is asymptotically exact for both strong and
weak local core-hole potentials and ultrashort lifetimes. The resonant
scattering pre-factor is shown to be weakly temperature dependent. We also
derive a sum-rule for the total scattering intensity and generalize the results
to multi-band systems. One of the remarkable outcomes is that one can change
the relative charge and spin contribution to the inelastic spectral weight by
varying the incident photon energy.Comment: 9 pages, 3 figures embedde
Resonant Inelastic X-ray Scattering on Spin-Orbit Coupled Insulating Iridates
We determine how the elementary excitations of iridium-oxide materials, which
are dominated by a strong relativistic spin-orbit coupling, appear in Resonant
Inelastic X-ray Scattering (RIXS). Whereas the RIXS spectral weight at the L2
x-ray edge vanishes, we find it to be strong at the L3-edge. Applying this to
Sr2IrO4, we observe that RIXS, besides being sensitive to local doublet to
quartet transitions, meticulously maps out the strongly dispersive delocalized
excitations of the low-lying spin-orbit doublets.Comment: 4 pages, 3 figure
Magnetic Excitations in La2CuO4 probed by Indirect Resonant Inelastic X-ray Scattering
Recent experiments on LaCuO suggest that indirect resonant inelastic
X-ray scattering (RIXS) might provide a probe for transversal spin dynamics. We
present in detail a systematic expansion of the relevant magnetic RIXS cross
section by using the ultrashort core-hole lifetime (UCL) approximation. We
compute the scattering intensity and its momentum dependence in leading order
of the UCL expansion. The scattering is due to two-magnon processes and is
calculated within a linear spin-wave expansion of the Heisenberg spin model for
this compound, including longer range and cyclic spin interactions. We observe
that the latter terms in the Hamiltonian enhance the first moment of the
spectrum if they strengthen the antiferromagnetic ordering. The theoretical
spectra agree very well with experimental data, including the observation that
scattering intensity vanishes for the transferred momenta and
. We show that at finite temperature there is an
additional single-magnon contribution to the scattering with a spectral weight
proportional to . We also compute the leading corrections to the UCL
approximation and find them to be small, putting the UCL results on a solid
basis. All this univocally points to the conclusion that the observed low
temperature RIXS intensity in LaCuO is due to two-magnon scattering.Comment: 11 pages, 13 figures, Phys. Rev. B 77, 134428 (2008) (v4: corrected
figs 7
Resonant Inelastic X-ray Scattering Studies of Elementary Excitations
In the past decade, Resonant Inelastic X-ray Scattering (RIXS) has made
remarkable progress as a spectroscopic technique. This is a direct result of
the availability of high-brilliance synchrotron X-ray radiation sources and of
advanced photon detection instrumentation. The technique's unique capability to
probe elementary excitations in complex materials by measuring their energy-,
momentum-, and polarization-dependence has brought RIXS to the forefront of
experimental photon science. We review both the experimental and theoretical
RIXS investigations of the past decade, focusing on those determining the
low-energy charge, spin, orbital and lattice excitations of solids. We present
the fundamentals of RIXS as an experimental method and then review the
theoretical state of affairs, its recent developments and discuss the different
(approximate) methods to compute the dynamical RIXS response. The last decade's
body of experimental RIXS data and its interpretation is surveyed, with an
emphasis on RIXS studies of correlated electron systems, especially transition
metal compounds. Finally, we discuss the promise that RIXS holds for the near
future, particularly in view of the advent of x-ray laser photon sources.Comment: Review, 67 pages, 44 figure