Realization of a three-dimensional spin–anisotropic harmonic honeycomb iridate

21 July 2014

Spin and orbital quantum numbers play a key role in the physics of Mott insulators, but in most systems they are connected only indirectly - via the Pauli exclusion principle and the Coulomb interaction. Iridium-based oxides (iridates) introduce strong spin-orbit coupling directly, such that these numbers become entwined together and the Mott physics attains a strong orbital character. In the layered honeycomb iridates this is thought to generate highly spin-anisotropic magnetic interactions, coupling the spin to a given spatial direction of exchange and leading to strongly frustrated magnetism with novel properties. In a recent paper in Nature Communications
"Realization of a three-dimensional spin–anisotropic harmonic honeycomb iridate" we report a new iridate structure that has the same local connectivity as the layered honeycomb and exhibits striking evidence for highly spin-anisotropic exchange. The basic structural units of this material suggest that a new family of three-dimensional structures could exist, the ‘harmonic honeycomb’ iridates, of which the present compound is the first example.

The contribution of the Oxford group comprising Mr Alun Biffin, Dr Sungkyun Choi, Dr Roger Johnson and lead by Dr Radu Coldea was to solve the crystal structure of this newly-synthesized material via single-crystal x-ray diffraction techniques using facilities in the Clarendon Laboratory.

This work is part of a larger research effort in Coldea's group to explore novel magnetism stabilized by strong spin-orbit coupling interactions (harmonic honeycomb Li2IrO3, layered honeycomb Na2IrO3).