Jahn-Teller effect in systems with strong on-site spin-orbit coupling

TL;DR

This paper investigates how the Jahn-Teller effect interacts with strong spin-orbit coupling in iridates, revealing that it influences spin-orbit excitons without disrupting the antiferromagnetic ground state, explaining experimental spectra features.

Contribution

It demonstrates that Jahn-Teller coupling affects spin-orbit excitons in iridates despite strong spin-orbit coupling suppressing orbital degeneracy, providing new insights into their spectral signatures.

Findings

Jahn-Teller effect does not affect the j_eff=1/2 ground state.

It enables hopping of j_eff=3/2 spin-orbit excitons between sites.

Jahn-Teller coupling explains features in RIXS spectra of Sr_2IrO_4.

Abstract

When strong spin-orbit coupling removes orbital degeneracy, it would at the same time appear to render the Jahn-Teller mechanism ineffective. We discuss such a situation, the t_2g manifold of iridates, and show that, while the Jahn-Teller effect does indeed not affect the j_eff=1/2 antiferromagnetically ordered ground state, it leads to distinctive signatures in the j_eff=3/2 spin-orbit exciton. It allows for a hopping of the spin-orbit exciton between the nearest neighbor sites without producing defects in the j_eff=1/2 antiferromagnet. This arises because the lattice-driven Jahn-Teller mechanism only couples to the orbital degree of freedom, but is not sensitive to the phase of the wave function that defines isospin j_z. This contrasts sharply with purely electronic propagation, which conserves isospin, and presence of Jahn-Teller coupling can explain some of the peculiar features of measured resonant inelastic x-ray scattering spectra of Sr_2IrO_4.