Resonant X-ray Scattering in Manganites - Study of Orbital Degree of Freedom -

Abstract

Orbital degree of freedom of electrons and its interplay with spin, charge and lattice degrees of freedom are one of the central issues in colossal magnetoresistive manganites. The orbital degree of freedom has until recently remained hidden, since it does not couple directly to most of experimental probes. Development of synchrotron light sources has changed the situation; by the resonant x-ray scattering (RXS) technique the orbital ordering has successfully been observed . In this article, we review progress in the recent studies of RXS in manganites. We start with a detailed review of the RXS experiments applied to the orbital ordered manganites and other correlated electron systems. We derive the scattering cross section of RXS where the tensor character of the atomic scattering factor (ASF) with respect to the x-ray polarization is stressed. Microscopic mechanisms of the anisotropic tensor character of ASF is introduced and numerical results of ASF and the scattering intensity are presented. The azimuthal angle scan is a unique experimental method to identify RXS from the orbital degree of freedom. A theory of the azimuthal angle and polarization dependence of the RXS intensity is presented. The theoretical results show good agreement with the experiments in manganites. Apart from the microscopic description of ASF, a theoretical framework of RXS to relate directly to the 3d orbital is presented. The scattering cross section is represented by the correlation function of the pseudo-spin operator for the orbital degree of freedom. A theory is extended to the resonant inelastic x-ray scattering and methods to observe excitations of the orbital degree of freedom are proposed.

47 pages, 24 figures, submitted to Rep. Prog. Phys

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• Resonant Soft X-ray Scattering Investigation of Orbital and Magnetic Ordering in $\mathrm{L}{\mathrm{a}}_{0.5}\mathrm{S}{\mathrm{r}}_{1.5}\mathrm{Mn}{\mathrm{O}}_4$
• Strain selection of charge and orbital ordering patterns in half-doped manganites
• The implications of resonant x-ray scattering data on the physics of the insulating phase of V${}_2$O${}_3$
• The Orbital Order Parameter in La0.95Sr0.05MnO3 probed by Electron Spin Resonance
• Vibronic order and emergent magnetism in cubic $d^1$ double perovskites
• Soft X-ray resonant scattering study of single-crystal LaSr${}_2$Mn${}_2$O${}_7$
• Fermi surface nesting and possibility of orbital ordering in FeO