Seminars Archive

From Charge to Orbitals: Ordering Phenomena Studied by Resonant (Soft/Hard) X-Ray Scattering

Abstract


Wednesday, June 15, 2005, 14:00


Seminar Room

Sincrotrone Trieste, Basovizza
From Charge to Orbitals: Ordering Phenomena Studied by Resonant (Soft/Hard) X-Ray Scattering




Urs Staub

(SLS, Villigen - Switzerland)
Abstract
It is shown how charge (monopoles), magnetic (dipoles) and orbitals (quadrupoles and higher multipoles) can be accessed by resonant X-ray scattering. Examples are given by the perovskite RNiO3, where hard and soft X-ray resonant X-ray scattering is used to study the charge and magnetic ordering of the Ni ions. The consistent interpretation of these signals and the absence of a detectable orbital contribution indicates that the unusual magnetic structure is not based on a particular scheme of orbital ordering. It is shown how these ordering phenomena relate to the metal-to-insulator transition. The second example concerns the layered manganite La0.5Sr1.5MnO4, where a detailed soft X-ray scattering study deduces the magnetic and orbital ordering. It is shown that polarization analysis and azimuthal scans are required to understand the observed signals. Moreover, the different temperature dependence of different features in the spectra points either to a strong interference of a magnetic signal originated by short range correlations with the orbital signal, or to a different order parameter of the Jahn-Teller distortion and the orbital ordering itself. In a last example, if time allows, higher-multipole ordering is discussed the 4f electron material DyB2C2. The energy dependence of the resonant soft X-ray scattering exhibits clear interference effects, which can be explained by an intra-atomic quadrupole interaction giving rise to a splitting of the core states. This makes the signal sensitive to quadrupoles (rank 2), hexadecapoles (rank 4) and hexacontatetrapoles (rank 6).