We have studied the magnetic excitations of electron-doped Sr2−xLaxIrO4 (0≤x≤0.10) using resonant inelastic x-ray scattering (RIXS) at the Ir L3-edge. The long range magnetic order is rapidly lost with increasing x, but two-dimensional short-range order (SRO) and dispersive magnon excitations with nearly undiminished spectral weight persist well into the metallic part of the phase diagram. The magnons in the SRO phase are heavily damped and exhibit anisotropic softening. Their dispersions are well described by a pseudospin-1/2 Heisenberg model with exchange interactions whose spatial range increases with doping. We also find a doping-independent high-energy magnetic continuum, which is not described by this model. The spin-orbit excitons arising from the pseudospin-3/2 manifold of the Ir ions broaden substantially in the SRO phase, but remain largely separated from the low-energy magnons. Pseudospin-1/2 models are therefore a good starting point for the theoretical description of the low-energy magnetic dynamics of doped iridates.
@article{arxiv.1603.07547,
title = {Persistent paramagnons deep in the metallic phase of Sr$_{2-x}$La$_x$IrO$_4$},
author = {H. Gretarsson and N. H. Sung and J. Porras and J. Bertinshaw and C. Dietl and Jan A. N. Bruin and A. F. Bangura and Y. K. Kim and R. Dinnebier and Jungho Kim and A. Al-Zein and M. Moretti Sala and M. Krisch and M. Le Tacon and B. Keimer and B. J. Kim},
journal= {arXiv preprint arXiv:1603.07547},
year = {2016}
}