Kitaev iridates in 3D: magnetic and structural instabilities*

Recent efforts were focused on the search for honeycomb antiferromagnets that realize Kitaev model in two dimensions. Despite showing sizable Kitaev couplings, Na₂IrO₃ and α-Li₂IrO₃ undergo long-range magnetic ordering at low temperatures and prove hard to be tuned by pressure, as compression leads to a dimerization instability and renders α-Li₂IrO₃ non-magnetic above 3.7 GPa.

Here, I will present recent results on the pressurized hyperhoneycomb iridate β-Li₂IrO₃ and argue that this compound can be tuned to a classical spin liquid state triggered by the reduction in the nearest-neighbor Kitaev term K and the enhancement of the off-diagonal anisotropy Γ. We find that above 1.4 GPa pressurized β-Li₂IrO₃ separates into a mixture of dynamic and frozen spins representing a partially frozen spin liquid, as expected in a system where spin dynamics is supported by thermal rather than quantum fluctuations.

I will further show how Kitaev magnetism is realized in three-dimensional frameworks of Ir⁴⁺ hexahalides that can be chemically tuned even at ambient pressure, thus giving rise to a variety of intertwined structural and magnetic instabilities.