Resonant
inelastic X-ray scattering (RIXS) is a powerful bulk-sensitive photon-in/photon-out
spectroscopic probe of the electronic structure with atomic and orbital
sensitivity. It is an ideal method for studying excitations from the electronic
ground state in correlated transition metal oxides, being directly sensitive to
charge-, orbital- and spin-degrees of freedom. Ultra-high resolution
instrumentation for RIXS is available at the ADvanced RESonant Spectroscopies
(ADRESS) beamline of the Swiss Light Source at the Paul Scherrer Institut,
being optimized for soft X-rays with variable polarization between 0.4 and 1.8
keV [1]. The SAXES (Super Advanced X-ray Emission Spectrograph) RIXS
spectrometer of the ADRESS beamline has a resolving power of ca. 12000 for 1
keV. It allows varying the scattering geometry between incident and inelastically
scattered X-rays in order to study low-energy excitations as a function of
momentum transfer. In this talk we give an overview on high-resolution and
momentum dependent RIXS studies of magnetic and electronic excitations in quasi
one-dimensional cuprate and oxide hetersotructure systems
Sr2CuO3
is a quasi one-dimensional corner-sharing single-chain compound possessing the
nearly ideal properties of the one-dimensional antiferromagnetic Heisenberg
spin-1/2 model. The momentum transfer dispersion of the Cu L3-RIXS signal in Sr2CuO3 along
the chain direction reveals that the main spectral weight follows the lower
onset of the two-spinon (and higher order) continuum and probes the dynamical
spin structure factor. Numerical calculations within the Bethe Ansatz allow a
detailed line shape analysis of the RIXS response. The modes within the orbital excitation energy range
show that the dd excitations in
Sr2CuO3 are
momentum dispersive and can be associated with orbitons, i.e. dispersive
excitations mediated by the superexchange interactions. A spin-orbital
superexchange model reproduces this orbiton dispersion and explains the large
dispersion with decoupling of the orbital and spin degree of freedom in this
one-dimensional system. Sr14Cu24O41 consists of two different
copper-oxide layers: the so-called spin-ladders and spin-chains. With Cu L3-RIXS we map out the
dispersion of two-triplon excitations, the elementary magnetic excitations in
the ladders, achieving excellent sensitivity over almost the full Brillouin-zone
and directly determining the two-triplon energy gap [2].
Oxide heterostructures have been attracting great
attention due to extraordinary phenomena occurring at the interface and their
potential application for device design employing oxide materials. A
particularly fascinating system is the two-dimensional conductive interface
between the band insulators LaAlO3 and SrTiO3, which can
be even driven to magnetic and superconducting phases at low temperature. Our
Ti L-RIXS studies on [(LAO)m/(STO)10]10
superlattices prepared by pulsed laser deposition unambiguously reveal two
types of carriers giving rise to localized and delocalized Ti 3d bands,
respectively [3]. Furthermore, high resolution RIXS measurements allow
quantifying the orthorhombic structural distortion of the Ti3+O6
octahedra at the LAO/STO interface.
[1]
G. Ghiringhelli et al., Rev. Sci. Instrum. 77, 113108 (2006);
V.
N. Strocov, T. Schmitt et al., J. Synchrotron Rad. 17, 631 (2010).
[2]
J. Schlappa, T. Schmitt, F. Vernay, V. Strocov et al., Phys. Rev. Lett. 103,
047401 (2009).
[3] K. J. Zhou, M.
Radovic et al., arXiv:1011.4674.