Two-magnon Raman scattering and pseudospin-lattice interactions in Sr2IrO4 and Sr3Ir2O7

TL;DR

This study uses Raman scattering to explore magnetic excitations and lattice interactions in Sr2IrO4 and Sr3Ir2O7, revealing two-magnon features and phonon anomalies linked to spin-orbit coupling effects.

Contribution

It provides new insights into the magnetic and lattice dynamics of iridates, highlighting the role of spin-orbit coupling and frustration in their excitations.

Findings

Distinct two-magnon Raman features in both compounds

Fano asymmetries in phonon lineshapes disappear below magnetic transition

Spin-orbit coupling influences orbital dynamics in the paramagnetic state

Abstract

We have used Raman scattering to investigate the magnetic excitations and lattice dynamics in the prototypical spin-orbit Mott insulators Sr2IrO4 and Sr3Ir2O7. Both compounds exhibit pronounced two-magnon Raman scattering features with different energies, lineshapes, and temperature dependencies, which in part reflect the different influence of long-range frustrating exchange interactions. Additionally, we find strong Fano asymmetries in the lineshapes of low-energy phonon modes in both compounds, which disappear upon cooling below the antiferromagnetic ordering temperatures. These unusual phonon anomalies indicate that the spin-orbit coupling in Mott-insulating iridates is not sufficiently strong to quench the orbital dynamics in the paramagnetic state.