We use resonant inelastic x-ray scattering (RIXS) at the Ir $L_3$ edge to study the effect of hole doping upon the $J_{\text{eff}}=\frac{1}{2}$ Mott-insulating state in ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$, via Rh replacement of the Ir site. The spin-wave gap, associated with XY-type spin-exchange anisotropy, collapses with increasing Rh content, prior to the suppression of the Mott-insulating state and in contrast to electron doping via La substitution of the Sr site. At the same time, despite heavy damping, the $d-d$ excitation spectra retain their overall amplitude and dispersion character. A careful study of the spin-wave spectrum reveals that deviations from the $J_1-J_2-J_3$ Heisenberg used to model the pristine system disappear at intermediate doping levels. These findings are interpreted in terms of a modulation of Ir-Ir correlations due to the influence of Rh impurities upon nearby Ir wave functions, even as the single-band $J_{\text{eff}}=\frac{1}{2}$ model remains valid up to full carrier delocalization. They underline the importance of the transition metal site symmetry when doping pseudospin systems such as ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$.

• Received 4 November 2019
• Revised 30 January 2020
• Accepted 4 March 2020

DOI:https://doi.org/10.1103/PhysRevB.101.094428

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Published by the American Physical Society