D−dexcitations in bilayer manganites probed by resonant inelastic x-ray scattering

Abstract

We report a high-resolution resonant inelastic x-ray scattering investigation of the bilayer manganites ${\text{La}}_{2\ensuremath{-}2x}{\text{Sr}}_{1+2x}{\text{Mn}}_{2}{\text{O}}_{7}$ with $x=0.36$ and 0.5. The momentum dependence along the crystallographic (110) direction for energy losses $1\text{ }\text{eV}\ensuremath{\le}\ensuremath{\Delta}E\ensuremath{\le}15\text{ }\text{eV}$ has been measured in detail with the data analysis focusing on the energy-loss region $1\text{ }\text{eV}\ensuremath{\le}\ensuremath{\Delta}E\ensuremath{\le}5\text{ }\text{eV}$, which includes a strong peak located at $\ensuremath{\Delta}E\ensuremath{\approx}2\text{ }\text{eV}$. We observe a clear dispersion of up to 0.5 eV in the measured $\mathbf{q}$ range, which is direct evidence of the nonlocal character of this excitation. Further, we found that the intensity in this low-energy region strongly depends on both the reduced wave vector $\mathbf{q}=(h,h,0)$, $h=0.1--0.5$, and temperature, i.e., different ordered phases. Results can be explained via an intersite $d\text{\ensuremath{-}}d$ charge-transfer excitation, proposed for pseudocubic manganites, where the hopping rate is strongly increased (decreased) by ferromagnetic (antiferromagnetic) alignment of neighboring in-plane Mn ion core spins.