Optical anisotropy of the Jeff = 1/2 Mott insulator Sr2IrO4

TL;DR

This study investigates the optical anisotropy of Sr2IrO4, revealing strong directional dependence in its dielectric response due to electronic transitions between specific iridium bands, supported by experimental and theoretical analysis.

Contribution

It provides detailed measurements of the dielectric function along different crystallographic axes and compares them with first-principle calculations, highlighting anisotropic optical properties in a Jeff=1/2 Mott insulator.

Findings

Identified 10 infrared-active phonon modes in-plane and 4 along c-axis.

Observed strong optical anisotropy in near-infrared spectra.

Transition probabilities between Ir 5d bands are highly polarization-dependent.

Abstract

We report the complex dielectric function along and perpendicular to the IrO2 planes in the layered perovskite Sr2IrO4 determined by spectroscopic ellipsometry in the spectral range from 12 meV to 6 eV. Thin high quality single crystals were stacked to measure the c-axis optical conductivity. In the phonon response we identified 10 infrared-active modes polarized within the basal plane and only four modes polarized along the c-axis, in full agreement with first-principle lattice dynamics calculations. We also observed a strong optical anisotropy in the near-infrared spectra arising from direct transitions between Ir 5d t2g Jeff = 1/2 and Jeff = 3/2 bands, which transition probability is highly suppressed for light polarized along the c-axis. The spectra are analyzed and discussed in terms of relativistic LSDA+U band structure calculations.