Z2xZ2 magnetic domains and magnetic moment disproportionation in the spin-orbit Mott insulator Sr2IrO4

Sr2IrO4 is representative of the new class of materials dubbed “spin-orbit Mott insulators” which hosts a variety of unconventional magnetism that arise from spin-orbit entangled moments, or pseudospins. A prominent example is the possible realization of a Kitaev spin liquid when pseudospins are arranged in a honeycomb lattice. In this talk, I will discuss on a new aspect of pseudospins; they show propensity to spontaneously disproportionate and lead to rich magnetic structures where symmetrically equivalent sites are decorated with magnetic moments of different magnitudes. We start by showing that the observed Z2xZ2 domain structure cannot be explained by the known magnetic structure and necessarily requires mixing of two order parameters that belong to two different irreducible representations of the high symmetry phase, which in response to the magnetic moment disproportionation distorts to a low symmetry phase. We argue that this phenomenon may be found more generally in other systems with spin-orbit entangled magnetic moments and hence should be considered when solving for the magnetic structure.