We report equilibrium and nonequilibrium optical measurements on the recently synthesized "harmonic" honeycomb iridate γ−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, ∆R, as a function of time, t, temperature, T , and probe field polarization in both LIO and NIO. In LIO, ∆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, ∆R(t, T ) has a single T dependent component that is strikingly similar to the electronic excitation component of ∆R in LIO. Through analysis and comparison of ∆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.

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We report the existence of a high temperature magnetic anomaly in the 3D Kitaev candidate material, β-Li2IrO3. Signatures of the anomaly appear in magnetization, heat capacity and muon spin relaxation measurements. The onset coincides with a reordering of the principal axes of magnetization which is thought to be connected to the onset of Kitaev-like correlations in the system. The anomaly also shows magnetic hysteresis with a spatially anisotropic magnitude that follows the spin-anisotropic exchange anisotropy of the underlying Kitaev Hamiltonian. We discuss possible scenarios for a bulk and impurity origin.