Magnetic excitations in the highly frustrated fcc iridate K₂IrCl₆

Magnetic materials with a high degree of geometrical frustration are prime candidates to realize exotic ground states governed by quantum fluctuations. K₂IrCl₆ is a model antiferromagnet with Ir⁴⁺ on a face-centered cubic lattice which is an exciting compound to explore Heisenberg-Kitaev exchange physics. The combination of crystal field and spin-orbit coupling renders a half-filled band of J_eff=1/2 character, which is localized by even moderate electronic correlations.[1] This J_eff=1/2 state and 90° Ir-O-Ir superexchange pathway favor both Heisenberg and Kitaev exchange interactions. In this talk, I will discuss inelastic neutron scattering measurements on K₂IrCl₆ and quantify the magnetic excitation spectra with a model including nearest and next-nearest neighbor Heisenberg interactions, Kitaev exchange and off-diagonal anisotropy. These measurements are essential to determine the Hamiltonian and thus where the material lies on the J-K-Γ phase diagram.

[1] J.Rau et al, Condensed Matter Phys. 7, 195 (2016)