Andrew Boothroyd

Abstract:

We have measured the spin-wave spectrum of the half-doped bilayer manganite Pr(Ca,Sr)2Mn2O7 in its spin, charge, and orbital ordered phase. The measurements, which extend throughout the Brillouin zone and cover the entire one-magnon spectrum, are compared critically with spin-wave calculations for different models of the electronic ground state. The data are described very well by the Goodenough model, which has weakly interacting ferromagnetic zig-zag chains in the CE-type arrangement. A model that allows ferromagnetic dimers to form within the zigzags is inconsistent with the data. The analysis conclusively rules out the strongly bound dimer (Zener polaron) model. © 2012 American Physical Society.

Abstract:

We report strongly momentum-dependent local charge screening dynamics in CE-type charge, orbital, and spin ordered La$_{0.5}$Sr$_{1.5}$MnO$_4$, based on Mn K-edge resonant inelastic x-ray scattering data. Through a comparison with theoretical calculations, we show that the observed momentum dependence reflects highly localized, nearest neighbor screening of the transient local charge perturbation in this compound with an exciton-like screening cloud, rather than delocalized screening. The size of the screening cloud is estmated to be about 0.4-0.5 interatomic distances.

Abstract:

The low-energy electronic structure of the J eff=1/2 spinorbit insulator Sr 3Ir 2O 7 has been studied by means of angle-resolved photoemission spectroscopy. A comparison of the results for bilayer Sr 3Ir 2O 7 with available literature data for the related single-layer compound Sr2IrO4 reveals qualitative similarities and similar J eff=1/2 bandwidths for the two materials, but also pronounced differences in the distribution of the spectral weight. In particular, photoemission from the J eff=1/2 states appears to be suppressed. Yet, it is found that the Sr 3Ir 2O 7 data are in overall better agreement with band-structure calculations than the data for Sr 2IrO 4. © 2012 IOP Publishing Ltd.