Photoexcited states of the harmonic honeycomb iridate \gamma-Li$_2$IrO$_3$

TL;DR

This study investigates the optical and photoinduced properties of the harmonic honeycomb iridate b3-LidIrOb3, revealing anisotropic magnetic and electronic excitations, and compares it with NadIrOb3 to understand magnetic correlations and quasiparticle dynamics.

Contribution

It provides the first detailed optical characterization of b3-LidIrOb3, highlighting its anisotropic photoinduced responses and their relation to magnetic order, advancing understanding of iridate quantum materials.

Findings

Identification of three temperature-dependent components in b3-LidIrOb3's photoinduced reflectance

Comparison with NadIrOb3 reveals similarities in electronic excitations

Insights into magnetic correlations and quasiparticle lifetimes in iridates

Abstract

We report equilibrium and nonequilibrium optical measurements on the recently synthesized "harmonic" honeycomb iridate \gamma-Li$_2$IrO$_3$ (LIO), as well as the layered honeycomb iridate Na$_2$IrO$_3$ (NIO). Using Fourier transform infrared microscopy we performed reflectance measurements on LIO, from which we obtained the optical conductivity below 2 eV. In addition we measured the photoinduced changed in reflectance, \Delta R, as a function of time, t, temperature, T, and probe field polarization in both LIO and NIO. In LIO, \Delta R(t,T) is anisotropic and comprised of three T dependent components. Two of these components are related to the onset of magnetic order and the third is related to a photoinduced population of metastable electronic excited states. In NIO, \Delta R(t,T) has a single T dependent component that is strikingly similar to the electronic excitation component of \Delta R in LIO. Through analysis and comparison of \Delta R(t,T) for two compounds, we extract information on the onset of magnetic correlations at and above the transition temperature in LIO, the bare spin-flip scattering rate in equilibrium, the lifetime of low-lying quasiparticle excitations, and the polarization dependence of optical transitions that are sensitive to magnetic order.