Giant magnetoelectric effect in the Jeff=1/2 Mott insulator Sr2IrO4

Our magnetic, electrical, and thermal measurements on single crystals of the J(eff)=1/2 Mott insulator, Sr2IrO4, reveal a giant magnetoelectric effect (GME) arising from a frustrated magnetic/ferroelectric state whose signatures are: (1) a strongly enhanced electric permittivity that peaks near an observed magnetic anomaly at 100 K, and (2) a large (similar to 100%) magnetodielectric shift that occurs near a metamagnetic transition. The GME hinges on a spin-orbit gapping of 5d bands rather than the magnitude and spatial dependence of magnetization, as traditionally accepted.