# Momentum-resolved lattice dynamics of parent and electron-doped Sr$_{2}$IrO$_{4}$

## TL;DR

This study uses high-resolution inelastic x-ray scattering to measure lattice dynamics in Sr$_{2}$IrO$_{4}$ and its electron-doped variant, revealing phonon behaviors consistent with density functional theory and no detectable anomalies related to magnetic or charge order.

## Contribution

First momentum-resolved lattice dynamics measurements for Sr$_{2}$IrO$_{4}$ and its doped form, providing insights into phonon behavior and couplings in this spin-orbit coupled material.

## Key findings

- Phonon dispersions match density functional theory calculations.
- No phonon anomalies detected across magnetic and charge ordering.
- Lattice properties are similar in parent and doped compounds.

## Abstract

The mixing of orbital and spin character in the wave functions of the $5d$ iridates has led to predictions of strong couplings among their lattice, electronic and magnetic degrees of freedom. As well as realizing a novel spin-orbit assisted Mott-insulating ground state, the perovskite iridate Sr$_{2}$IrO$_{4}$ has strong similarities with the cuprate La$_{2}$CuO$_{4}$, which on doping hosts a charge-density wave that appears intimately connected to high-temperature superconductivity. These phenomena can be sensitively probed through momentum-resolved measurements of the lattice dynamics, made possible by meV-resolution inelastic x-ray scattering. Here we report the first such measurements for both parent and electron-doped Sr$_{2}$IrO$_{4}$. We find that the low-energy phonon dispersions and intensities in both compounds are well described by the same nonmagnetic density functional theory calculation. In the parent compound, no changes of the phonons on magnetic ordering are discernible within the experimental resolution, and in the doped compound no anomalies are apparent due to charge-density waves. These measurements extend our knowledge of the lattice properties of (Sr$_{1-x}$La$_{x}$)$_{2}$IrO$_{4}$ and constrain the couplings of the phonons to magnetic and charge order.