Charge excitations in stripe-ordered La_5/3Sr_1/3NiO_4 and La_15/_8Ba_1/8CuO_4: Interpretation of the anomalous momentum transfer dependence via fluorescence interferometry

摘要

Fluorescence interferometry (FI) makes use of the temporal and spatial coherence of absorption and re-emission process in resonant inelastic x-ray scattering (RIXS), which leads to interference terms in the RIXS cross section of a group of identical, physically equivalent, and interacting atoms. These interferences contain structural information and make RIXS site selective. The basics of FI are derived within the third-order perturbation treatment of indirect RIXS. The final relations for the FI related RIXS cross section were used to interpret the unique momentum-transfer dependence of the in-gap charge excitations observed for 214-type nickelates (La_5/3Sr_1/3NiO_4) and cuprates (La_15/8Ba_1/gCuO_4). By using well-known stripe models, the momentum-transfer dependence of the corresponding indirect RIXS features is traced back to interference terms in the RIXS cross section based on the principles of FI. Thus analyzing the momentum-transfer dependence of the re-emitted radiation yields information about details of the charge stripe structure.